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Speaker 1: You often hear that space is vast and mostly empty.

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Speaker 1: That's all true, but it gives you the impression that

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Speaker 1: our cosmic home is alone in the universe. But we're not.

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Speaker 1: We have a nice bright star to keep us warm

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Speaker 1: and push back the darkness, and other planets are there

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Speaker 1: to help protect us from interstellar interlopers. And our sun

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Speaker 1: is part of a massive swarm of stars in the

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Speaker 1: Milky Way, home to hundreds of billions of planetary cousins.

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Speaker 1: It's actually kind of a cozy cosmic neighborhood. But is

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Speaker 1: that true for all planets and stars? Could there be

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Speaker 1: planets existing outside of a solar system, floating in the

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Speaker 1: dark of space on their own, or could a star

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Speaker 1: form outside a galaxy? Could either of these be host

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Speaker 1: to life who would evolve and see a very different

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Speaker 1: view of the universe. Today On the pod will dive

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Speaker 1: into how planets and stars form and whether any or

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Speaker 1: many exist out there on their own. Welcome to Daniel

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Speaker 1: and Kelly's extraordinarily rogue Universe.

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Speaker 2: Hi. I'm Kelly Winersmith. I study parasites and space.

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Speaker 1: Hi I'm Daniel. I'm a particle physicist and I like

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Speaker 1: to think of myself as a rogue scientist.

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Speaker 2: Oh nice, I could think of myself as a rogue side.

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Speaker 2: I mean, you're like in academia and you're funded by

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Speaker 2: the Department of Defense or something, right, how are you

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Speaker 2: a rogue scientist?

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Speaker 1: Excuse me? I have no Department of Defense or Department

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Speaker 1: of War funding at all. None of my research can

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Speaker 1: be used to kill people, Thank you very much.

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Speaker 2: Sorry. Who is it that's given you like lifetime funding?

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Speaker 2: Is that the Department of Energy?

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Speaker 1: There is no lifetime funding guarantee. But I have been

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Speaker 1: supported by the Department of Energy since I was ten

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Speaker 1: years old.

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Speaker 2: Ten. Now, Daniel, you're brilliant. I have no doubt that

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Speaker 2: you could have started physics research at ten. But was

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Speaker 2: the Department of Energy funding your parents? I'm guessing yeah, exactly.

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Speaker 1: Okay, they put food on the table since I was ten. Yeah.

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Speaker 2: Nice.

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Speaker 1: But my research direction is sort of off the beaten path,

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Speaker 1: within the larger confines of academia. So that's why I

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Speaker 1: think myself is a realgue scientist, and you must as well.

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Speaker 1: You're a pretty unusual character in your community, aren't you.

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Speaker 2: Yes, I am, although like many scientists, I'm underpaid. So uh,

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Speaker 2: that's all right. I love what I do, I don't care.

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Speaker 1: And all of us rogues come together to make a

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Speaker 1: cozy community of rogue sciences. Nobody is on their own,

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Speaker 1: and that's the topic of today's episode. Our cosmic community,

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Speaker 1: our cosmic neighborhood. Where are we in the universe? And

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Speaker 1: do we have neighbors in far flung, distant, dark reaches

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Speaker 1: of space.

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Speaker 2: That's right, We're not alone, and thankfully for us, we're

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Speaker 2: kept company by the community of extraordinaries who share their

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Speaker 2: questions with us.

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Speaker 1: We adore the adordinaries.

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Speaker 2: I feel like we're stretching it a little bit.

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Speaker 1: Well. We love hearing from all of you. We love

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Speaker 1: hearing what you are wondering about. We love being inspired

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Speaker 1: by your curiosity, and we love when you write to

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Speaker 1: us to ask us questions. And today we have an

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Speaker 1: episode inspired by a question from a listener. Here's Steve's question.

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Speaker 3: Hi, Daniel and Kelly. I was looking at the stars

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Speaker 3: last night, and I know galaxies are full of stars,

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Speaker 3: but are there any stars not in a galaxy and

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Speaker 3: floating around by themselves? In that same vein, is there

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Speaker 3: a planet floating around without orbiting a sun? Thanks?

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Speaker 2: Oh, rogue planets and suns. I love it. What a

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Speaker 2: great question, and please send us your questions at questions

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Speaker 2: at Daniel and Kelly dot org. We answer every emo

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Speaker 2: we get, and a subset of them will end up

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Speaker 2: getting answered on air.

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Speaker 1: This is such a great question because you can hear

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Speaker 1: Steve wondering if we are weird in the universe, if

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Speaker 1: our situation is tip like, are all planets and stars

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Speaker 1: out there in galaxies like we are? Or are there

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Speaker 1: other situations? And this is exactly the kind of thinking

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Speaker 1: that breaks us out of the box and helps us

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Speaker 1: understand the universe, because in lots of situations we are typical,

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Speaker 1: and in lots of situations we are weird. So it's

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Speaker 1: important to ask these questions and then go out and

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Speaker 1: take measurements and demand that the universe give us answers well.

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Speaker 2: And so often when someone sends us a question, it's

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Speaker 2: a question that a lot of other people haven't thought

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Speaker 2: about either. And so we wanted to know has our

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Speaker 2: audience thought about rogue planets and rogue suns? So we

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Speaker 2: asked them, We asked the extraordinaries, are there rogue planets

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Speaker 2: and rogue suns?

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Speaker 4: I would say pretty common.

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Speaker 3: Space is just so big and vast that I just

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Speaker 3: don't think it's really going to affect us, much like

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Speaker 3: there's so many rogue planets out there because the initial

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Speaker 3: conditions of solar systems are super chaotic.

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Speaker 2: I think rogue planets and rogue stars are more common

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Speaker 2: than we may think.

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Speaker 1: I don't think there's a discovery yet, as these would

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Speaker 1: be so dim, so often one of them is flung

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Speaker 1: out with quite a large velocity. I think we've seen

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Speaker 1: quite a few of those are observed, at least a

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Speaker 1: handful of them.

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Speaker 3: There are probably a lot of rogue planets and stars

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Speaker 3: out there.

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Speaker 1: Even just one instance of a galaxy collision would disrupt

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Speaker 1: a significant number of solar systems, so I would venture

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Speaker 1: to guess there are hundreds of millions, if not billions.

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Speaker 1: I don't think they are common at all, otherwise we

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Speaker 1: will be hearing about them all the time.

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Speaker 5: I suspect they are quite uncommon from what I've read

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Speaker 5: and what I've heard from credible podcasts. Not aislot is

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Speaker 5: that rogue plants are quite common. However, I've heard nothing

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Speaker 5: about rogue stars. So the only rogue star I could

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Speaker 5: think of is p Diddy, because girl he went rogue.

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Speaker 1: I'd guess there's probably a lot of them, maybe even

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Speaker 1: more than the well behaved kind.

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Speaker 4: Yeah, for once, physics went with an awesome name. Rogue

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Speaker 4: planets is just such a cool thing to call them.

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Speaker 4: I think I heard that one three exoplanets are rogue planets,

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Speaker 4: so they must be incredibly colon And I also think

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Speaker 4: I had that there are quite a lot of rogue

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Speaker 4: stars as well, So I think there are loads of

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Speaker 4: rogue planets, quite a lot of rogue stars.

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Speaker 3: I know Kelly doesn't like the names of many of

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Speaker 3: the concepts in physics, but rogue star and rogue planets

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Speaker 3: are great titles.

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Speaker 2: I totally agree. I am so proud of physicists for

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Speaker 2: coming up with a good name for once rogue planets

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Speaker 2: and rogues our data was that just a Daniel flourish

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Speaker 2: Do you all actually refer to them?

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Speaker 1: Okay, all right, I can't take credit for that one,

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Speaker 1: but I agree it's a good name. It's cool, and

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Speaker 1: it snappily describes what it really is.

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Speaker 2: That's right way to go. Physicists. Keep in mind that

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Speaker 2: this can go well.

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Speaker 1: We just do that occasionally to raise your hopes, and

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Speaker 1: then we disappoint you over and over again.

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Speaker 2: Oh my gosh, so much disappointment these days. All right,

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Speaker 2: let's get started, because I'm kind of dying to know.

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Speaker 2: I also did not know the answer to this question

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Speaker 2: before you sent me the outline, and I didn't read

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Speaker 2: the outline very well, Daniel, So I'm still not sure

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Speaker 2: I know the answer.

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Speaker 1: So for a dramatic effect, I'm unprepared.

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Speaker 2: Nice, that's right. So before we talk about rogue planets

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Speaker 2: and stars, how about we just talk about normal stars

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Speaker 2: and planets. How are normal stars and planets formed?

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Speaker 1: Yeah, it's important to know where stars and planets come from,

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Speaker 1: so we can figure out whether there are any stars

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Speaker 1: and planets out there in the black of space on

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Speaker 1: their own, like could they form out there by themselves,

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Speaker 1: et cetera. And the understanding of how we get stars

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Speaker 1: and planets is incredible because it's one of the great

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Speaker 1: triumphs of our understanding of the universe. We have now

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Speaker 1: an explanation for how you go from like a hot

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Speaker 1: dense soup in the early universe with a few over

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Speaker 1: densities and a few under densities, a few spots with

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Speaker 1: like more stuff and a few spots with less stuff,

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Speaker 1: and evolve that forward in time to get the structure

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Speaker 1: of the universe that we see today. Briefly, the spots

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Speaker 1: with more stuff have more gravity and track more stuff together,

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Speaker 1: and then it clumps and that just keeps happening, so

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Speaker 1: that you go from a spread out soup of stuff

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Speaker 1: where everything is very close to the same density, to

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Speaker 1: spots of incredible density like stars and other places with

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Speaker 1: massive voids in them.

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Speaker 2: That sounds pretty intuitive. Are we like super confident that

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Speaker 2: this is how stars form? Where is this like the

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Speaker 2: current hypothesis? And we feel pretty good about it.

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Speaker 1: We're very confident in this story because there's so many

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Speaker 1: elements to it that come together. For example, the way

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Speaker 1: galaxies form is that these massive clouds of gas come together,

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Speaker 1: become dense, and then form stars. But if you just

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Speaker 1: run a simulation of the universe starting from those over

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Speaker 1: densities and letting the clock go fourteen billion years, you

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Speaker 1: actually don't see galaxy formation because there's not enough gravity

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Speaker 1: just from gas and dust and all that stuff to

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Speaker 1: form galaxies. You need help from dark matter. Dark matter

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Speaker 1: is most of the matter in the universe, so it

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Speaker 1: provides most of the gravity, and dark matter forms these

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Speaker 1: wells into which gas flows and forms these halos where

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Speaker 1: you get star formation, So dark matter shapes the whole

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Speaker 1: structure of the universe. When you add dark matter into

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Speaker 1: those simulations, then you do see galaxy formation and structure formation,

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Speaker 1: and galaxy clusters and all the crazy stuff that we

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Speaker 1: see out there in the universe. Not our exact galaxies.

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Speaker 1: Of course, we can't model that because we don't know

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Speaker 1: the initial conditions. But the typical distributions of galaxies and

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Speaker 1: clusters and all that kind of stuff all comes out

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Speaker 1: beautifully in these simulations if you add the mixture of

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Speaker 1: normal matter and dark matter that we have in our universe.

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Speaker 2: All right, two thoughts. First thought, if I had created

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Speaker 2: that simulation and what popped out was like a really

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Speaker 2: nice simulation of the universe, Like I can't even imagine

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Speaker 2: how cool that must have been to see that on

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Speaker 2: your screen and be like, oh, I did it. I

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Speaker 2: understand the universe. Like that sounds amazing. But remind me,

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Speaker 2: dark matter, dark energy one of them, maybe both we

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Speaker 2: don't understand very well.

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Speaker 1: We don't understand either of them very well, but we

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Speaker 1: understand dark matter a lot better. The dark matter we

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Speaker 1: know it's some kind of matter that's out there in

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Speaker 1: the universe. It's invisible, it's intangible as far as we

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Speaker 1: can tell. But it does provide gravity, and we know

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Speaker 1: a lot about where it is and how it flows,

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Speaker 1: and it's temperature, it's quite cold, but we don't know

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Speaker 1: what it's made out of it a particle level. But

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Speaker 1: this is just like one independent line of dark matter evidence.

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Speaker 1: We need it to make the large scale structure of

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Speaker 1: the universe and also to make galaxy spin. And also

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Speaker 1: it explained wiggles in their early universe radiation and all

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Speaker 1: sorts of independent lines of evidence. Dark energy we know

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Speaker 1: almost nothing about. We know the universe is expanding and

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Speaker 1: that expansion is accelerating. We don't understand the mechanism we

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Speaker 1: call that dark energy, but we also need that to

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Speaker 1: explain the structure of the universe because it helps power

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Speaker 1: the expansion of the universe. Anyway, back to stars. Dark

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Speaker 1: matter and these initial over densities give you these clumps

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Speaker 1: of gas and dust and those cool and then they

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Speaker 1: form stars. In order to form stars, you need like

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Speaker 1: some seed, like a gravitational density, but you also need

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Speaker 1: the gas there to be kind of cold, because if

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Speaker 1: it's too hot, if they're moving too fast, then gravity

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Speaker 1: which is pretty weak in the end, can't grab onto

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Speaker 1: these tiny gas atoms and collapse them together. So once

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Speaker 1: it cools down to like ten or twenty kelvin, then

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Speaker 1: it collapses into these stars. These pockets of densities become protostars,

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Speaker 1: which get heavier and heavier, and eventually they get enough

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Speaker 1: mass that there's enough pressure at the core to raise

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Speaker 1: that temperature up to get fusion, and that's how stars form.

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Speaker 2: Okay, And I'm finding myself wondering why didn't everything just

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Speaker 2: get sucked into the Sun because it's massive, And I

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Speaker 2: guess it's because everything else is moving so fast it's

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Speaker 2: able to keep orbit instead of getting sucked in. Is

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Speaker 2: that right?

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Speaker 1: Yeah, it's a great question. You might also ask, like,

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Speaker 1: why don't we just get one mega sun? Yeah, right,

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Speaker 1: instead of lots and lots of suns. It's because you

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Speaker 1: have pockets of density. That's why you get lots of

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Speaker 1: stars instead of individual ones, so each one forms a seed,

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Speaker 1: and the same thing happens in the Solar system. We'll

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Speaker 1: dig into this in a minute when we talk about planets.

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Speaker 1: But some things are going too fast to fall in immediately,

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Speaker 1: and there are little gravitational over densities on the outer

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Speaker 1: edge of these gas blobs, which then rush together to

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Speaker 1: grab some gas before it all gets sucked into the Sun. Okay,

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Speaker 1: so yeah, absolutely, And so the crucial thing to understand

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Speaker 1: here is that stars do not form out in the

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Speaker 1: middle of space. They form in these huge clouds that

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Speaker 1: eventually leads to galaxies. And one way we know this

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Speaker 1: is that when we look at stars, we often find

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Speaker 1: them in binary star systems. Stars, even in galaxies, are

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Speaker 1: not made on their own. They're typically made with siblings, two, three,

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Speaker 1: sometimes seven stars all berthed together, and you find them

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Speaker 1: still near each other out there. So stars are not

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Speaker 1: made all on their lonesome. They're made in these vast

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Speaker 1: nurseries where huge clouds of gas are collapsing into stars.

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Speaker 2: And it's impossible for that whole cloud to collapse into

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Speaker 2: one thing, or just like incredibly improbable.

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Speaker 1: It's improbable. Though. We think that in the early universe,

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Speaker 1: in the first round of collapse of stars, some of

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Speaker 1: those stars were really monsters, like three hundred times the

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Speaker 1: mass of our sun, because you didn't have any metals yet.

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Speaker 1: It was all just hydrogen and tiny bits of helium,

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Speaker 1: so things were sort of smoother later on when you'd

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Speaker 1: form metals. Those metals were excellent seeds, so you ended

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Speaker 1: up getting more smaller stars. But in the early universe

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Speaker 1: we think there were some really huge monster stars that

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Speaker 1: were formed. But there's also sort of an upper limit

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Speaker 1: on the size of a star, around three hundred times

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Speaker 1: the mass of our sun, because bigger than that, the

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Speaker 1: core gets so hot that fusion rips apart. The star

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Speaker 1: and the stars are a balance between gravity that's collapsing

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Speaker 1: it and fusion that's providing pressure to keep it from collapsing.

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Speaker 1: If fusion gets too hot, and fusion increases very rapidly

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Speaker 1: with temperature, then it blows the star apart. So that's

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Speaker 1: why you didn't get super huge galaxies that are just

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Speaker 1: like one star, which would be kind of awesome, but

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Speaker 1: it doesn't really work with physics.

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Speaker 2: Lonely it would be lonely exactly, all right. So now

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Speaker 2: we've tackled stars, what about planets? How does a planet form?

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Speaker 1: Yeah, so planets are sort of the leftover bits of

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Speaker 1: that formation. You have this cloud of gas that's collapsing,

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Speaker 1: but you have other puck it's a density. You have

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Speaker 1: like a little bit of metal from an earlier star

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Speaker 1: or a chunk of rock that forms the seed, and

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Speaker 1: the rest of the cloud is either molecules of hydrogen

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Speaker 1: or like micron sized dust greens, which can come together

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Speaker 1: and stick together with like very weak vander Walls forces,

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Speaker 1: and this just accumulates and you get like another seed.

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Speaker 1: So if your disk of gas is very, very smooth,

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Speaker 1: you might not get any planets, but that's very unlikely

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Speaker 1: because typically there are little clumps of gravitational over density

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Speaker 1: that will then form the seed of little sort of

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Speaker 1: mini collapses. For the same reason that you don't get

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Speaker 1: one megastar from a molecular cloud, you also don't just

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Speaker 1: have a collapse into one object. Though the star does

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Speaker 1: gobble most of the mass in the Solar System because

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Speaker 1: it forms first and it's big and it's massive and

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Speaker 1: so gobbles like ninety nine percent of the material. But

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Speaker 1: if you're far away from the star, you also can

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Speaker 1: take advantage of ice. If you're far enough away that,

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Speaker 1: like the star's radiation is not instantly vaporizing all ice,

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Speaker 1: then you have another solid material you can use to

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Speaker 1: build your planet.

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Speaker 2: I mean, it doesn't make me feel great that planets

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Speaker 2: are like star crumbs, but I'll take it are there

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Speaker 2: any solar systems we've seen that have only one planet? Like,

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Speaker 2: what's the average number of planets in a solar system? Daniel,

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Speaker 2: surely you have that at your fingertips.

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Speaker 1: We have seen a lot of planets out there, something

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Speaker 1: more than like five thousand or so by now. And

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Speaker 1: in some solar systems we've only seen one planet because

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Speaker 1: it's like a big one and it's close to the star,

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Speaker 1: so it's easier to spot because being close to the

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Speaker 1: star means it's like a bigger eclipse of the star,

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Speaker 1: so we can use the transit method. Or a massive

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Speaker 1: planet means it's pulling on the stars, so we can

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Speaker 1: use the wiggle method. So we don't know necessarily, but

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Speaker 1: we suspect that most stars have many planets based on

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Speaker 1: other observations, and then extrapolating and also from models is

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Speaker 1: very unlikely to get a single individual planet. But there's

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Speaker 1: still lots of uncertainty.

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Speaker 2: Hear.

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Speaker 1: The theory I've just described is called the quark accretion

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Speaker 1: model that you start with like a little clump and

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Speaker 1: you gather more stuff around it to make a planet.

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Speaker 1: There are other theories. Is one called like the gravitational

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Speaker 1: instability theory, that like an entire planet can form from

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Speaker 1: a gravitation collapse all at once rather than gradually wo

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Speaker 1: and neither theory perfectly describes everything we see. We can

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Speaker 1: look out now into space and see planets form, because remember,

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Speaker 1: looking into space is looking backwards in time. And sometimes

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Speaker 1: we can spot a star in formation and you can

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Speaker 1: see that like the protoplanetary ring around it after only

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Speaker 1: like you know, half a million years or so, and

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Speaker 1: can help us test our theories of formation. And sometimes

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Speaker 1: we see like huge planets and multiple planetary rings and

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Speaker 1: all sorts of crazy stuff that we don't really understand.

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Speaker 1: It's often like this that we see things happening more

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Speaker 1: quickly in the universe than we expect, and so it

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Speaker 1: updates our model. So we definitely don't have a perfect

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Speaker 1: theory of planet formation yet.

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Speaker 2: Okay, so quick summary. The Sun, we feel super confident

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Speaker 2: in how that is formed. Planet's a little less confident.

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Speaker 1: Yeah, that's true. But the bottom line is that in general,

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Speaker 1: stars and planets are made in big clumps, in huge

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Speaker 1: clouds of dust and gas. They're not made out on

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Speaker 1: their own. You don't just get like a planet randomly

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Speaker 1: forming in the middle of space.

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Speaker 2: All right, done. Thanks for the question, and we'll see

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Speaker 2: you next week. Oh no, wait, there's more, Oh so

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Speaker 2: much more, so much more. After the break, we'll give

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Speaker 2: you more, all right. So daniel just finished telling us

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Speaker 2: how the Sun is formed and how planets are formed,

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Speaker 2: and it sounds like you shouldn't get rogue stars and planets,

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Speaker 2: but you know, this is physics, and so nothing is

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Speaker 2: as it seems. What happens to give us rogue stars

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Speaker 2: and planets, Danielle, Well, what we.

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Speaker 1: Just learned is where stars and planets are made. That

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Speaker 1: doesn't limit stars and planets to stay there forever. Right,

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Speaker 1: Lots of people grow up and then move away from home,

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Speaker 1: and so stars and planets might also be able to

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Speaker 1: do that. But what this means is that to get

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Speaker 1: rogue stars and planets you have to somehow form them

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Speaker 1: in galaxies and then eject them. Right, we need some

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Speaker 1: method to get them out of the galaxies if they're

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Speaker 1: going to be out there in the middle of space.

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Speaker 1: And so let's start with rogue stars. Stars were very

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Speaker 1: confident begin in galaxies, although I'll add we talked about

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Speaker 1: the development of stars as if that's where all the

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Speaker 1: gas in dust is. But there's an enormous amount of

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Speaker 1: gas between galaxies as well. There are these huge filaments

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Speaker 1: of gas connecting the individual gravitational wells. Something like half

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Speaker 1: of all the baryons. The normal matter in the universe

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Speaker 1: is outside of galaxies. It's just very very dilute and

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Speaker 1: very very hot. So it's not the place where stars

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Speaker 1: will form, but it's not like it's really empty space.

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Speaker 1: Incredible filaments of gas connecting all the galaxies.

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Speaker 2: I love that that. You know, you connected these rogue

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Speaker 2: stars to like humans moving away, and now we've got

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Speaker 2: this other connection here. You know, the universe is full

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Speaker 2: of gas and so are humans, and I just I'm

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Speaker 2: feeling celestial today.

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Speaker 1: Yeah, exactly. Well maybe people move out because they were

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Speaker 1: too full of gas and their families couldn't stand it.

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Speaker 2: Oh, be gone.

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Speaker 1: So the crucial question to understanding how a star can

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Speaker 1: leave the galaxy is essentially like escape velocity. How can

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Speaker 1: it get out of the galaxy? Galaxies exist for a

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Speaker 1: reason because they have a lot of gravity. They tend

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Speaker 1: to hang on to their stars that's where they're formed,

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Speaker 1: and there's so much mass there that like, for example,

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Speaker 1: our Sun is orbiting the center of the galaxy and

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Speaker 1: it takes a few hundred million years to go all

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Speaker 1: the way around, but it's unlikely to just like wander

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Speaker 1: out of the galaxy. It is bound there, right, And

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Speaker 1: we think we understand the gravitational dynamics of galaxies. This

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Speaker 1: is how we first discovered dark matter. We saw that

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Speaker 1: stars are not being thrown into intergalactic space very often

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Speaker 1: because they're something in the galaxy providing that gravity to

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Speaker 1: hold them together. All right, but that doesn't mean that

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Speaker 1: it's impossible. It just means you need a lot of speed,

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Speaker 1: sometimes up to thousands or millions of kilometers per hour, wow,

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Speaker 1: and that can happen. We know also that galaxies form

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Speaker 1: in the method we just describe, but then they also combine. Right,

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Speaker 1: the method we talked about makes essentially a bunch of

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Speaker 1: little baby galaxies. But if we look at galaxies today,

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Speaker 1: they're big, they're huge, and they show evidence of collisions

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Speaker 1: of mergers. So the Milky Way, for example, is a

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Speaker 1: combination of a bunch of little galaxies which came together.

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Speaker 1: And when galaxies come together, it's sometimes peaceful, but often

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Speaker 1: it's chaotic, and what happens is some stars get tossed

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Speaker 1: into space.

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Speaker 2: I have to admit I'm a little biased towards a

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Speaker 2: particular listener question, and that was my daughter's listener question,

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Speaker 2: because I think she asked you if our Sun was

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Speaker 2: thrown out of another galaxy and ended up where it

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Speaker 2: is today, and I think you said no, Is that right?

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Speaker 1: Yeah, I don't remember any detail because we answer so

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Speaker 1: many questions and we're trying to be democratic about the

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Speaker 1: manacho any favoritism. Oh, but I'm glad that you remember.

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Speaker 1: So in that sense, it's true that our star has

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Speaker 1: always been a member of the Milky Way. But it's

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Speaker 1: also possible that it was a member of another galaxy

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Speaker 1: which informed and became the Milky Way, like joined with

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Speaker 1: the Milky Way. Though our star is fairly young for

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Speaker 1: the Milky Way, like the Milky Way is almost as

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Speaker 1: old as the universe, and our Star is only a

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Speaker 1: few billion years old, So it's also possible that are

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Speaker 1: formed in the Milky Way.

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Speaker 2: Wow, Okay, cool. So sometimes galaxies combine, and how exactly

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Speaker 2: does that result in something getting kicked out so that

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Speaker 2: it's no longer part of the club.

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Speaker 1: Yeah. So you have these two galaxies, each of which

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Speaker 1: is already spinning, right, and now they come in and

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Speaker 1: they combine, they form a new center of mass. And

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Speaker 1: some things naturally have the right velocity in the right

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Speaker 1: distance and the right direction in order to be orbiting

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Speaker 1: the new center of mass. But sometimes they don't, and

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Speaker 1: the new center of mass has like a gravity to

438
00:22:02,400 --> 00:22:05,240
Speaker 1: tug on that star and just eject it. And so

439
00:22:05,320 --> 00:22:08,639
Speaker 1: it's not guaranteed that everything in the old galaxies finds

440
00:22:08,640 --> 00:22:11,159
Speaker 1: a new stable orbit in the new galaxies.

441
00:22:11,280 --> 00:22:13,240
Speaker 2: It's a real drag when things change.

442
00:22:13,359 --> 00:22:15,720
Speaker 1: It can exactly. And remember that at the hearts of

443
00:22:15,760 --> 00:22:20,760
Speaker 1: these galaxies are super massive black holes, these enormously massive,

444
00:22:21,000 --> 00:22:24,679
Speaker 1: very dense, compact objects we don't understand very well that

445
00:22:24,720 --> 00:22:27,159
Speaker 1: can provide a huge gravitational boost. And so if the

446
00:22:27,200 --> 00:22:30,000
Speaker 1: new stars coming in get close to the supermassive black

447
00:22:30,000 --> 00:22:32,800
Speaker 1: hole of the other galaxy Boom, they can very easily

448
00:22:32,800 --> 00:22:35,320
Speaker 1: get ejected wow or even without a merger. If a

449
00:22:35,359 --> 00:22:38,040
Speaker 1: star wanders too close to the super massive black hole

450
00:22:38,080 --> 00:22:40,560
Speaker 1: in our galaxy, for example, then it can get a

451
00:22:40,560 --> 00:22:43,359
Speaker 1: big kick and become what they call a hypervelocity star.

452
00:22:43,600 --> 00:22:46,600
Speaker 2: WHOA How do we detect and measure this stuff?

453
00:22:46,880 --> 00:22:50,080
Speaker 1: So, of course space telescopes when if humanity's greatest invention

454
00:22:50,240 --> 00:22:52,440
Speaker 1: give more money. We can look at these stars and

455
00:22:52,560 --> 00:22:55,359
Speaker 1: we can measure their velocity by looking at the red shift.

456
00:22:55,720 --> 00:22:57,359
Speaker 1: We know how a star should admit light at what

457
00:22:57,440 --> 00:23:00,280
Speaker 1: frequencies because we know what they're made out of, and

458
00:23:00,320 --> 00:23:01,920
Speaker 1: we can look at the spectrum and say, oh, look,

459
00:23:01,920 --> 00:23:04,920
Speaker 1: there's hydrogenous helium, there's other stuff in the atmosphere of

460
00:23:04,960 --> 00:23:07,960
Speaker 1: this star. But if we see those things shifted from

461
00:23:07,960 --> 00:23:10,520
Speaker 1: the fingerprints where we expect to see them, then we

462
00:23:10,680 --> 00:23:13,680
Speaker 1: know that the star has a velocity. Because a velocity

463
00:23:13,680 --> 00:23:16,600
Speaker 1: from the star will give a Doppler shift, will change

464
00:23:16,640 --> 00:23:18,840
Speaker 1: the light. It will red shift all the light from

465
00:23:18,840 --> 00:23:21,640
Speaker 1: that star. So a star moving away from us will

466
00:23:21,640 --> 00:23:24,240
Speaker 1: be redder and a star moving towards us will be bluer.

467
00:23:24,480 --> 00:23:26,600
Speaker 1: So by looking at the spectrum of the star, you

468
00:23:26,640 --> 00:23:29,440
Speaker 1: can measure the velocity of the star. This is how

469
00:23:29,480 --> 00:23:31,600
Speaker 1: we see that most of the universe is moving away

470
00:23:31,600 --> 00:23:34,040
Speaker 1: from us by looking at the red shift of stars

471
00:23:34,040 --> 00:23:36,880
Speaker 1: in other galaxies. We can also do that for individual

472
00:23:36,920 --> 00:23:40,360
Speaker 1: stars within our galaxy. And we've been doing that for

473
00:23:40,400 --> 00:23:42,080
Speaker 1: like twenty or thirty years now.

474
00:23:41,920 --> 00:23:45,520
Speaker 2: WHOA so how often have we seen something being ejected?

475
00:23:45,720 --> 00:23:47,960
Speaker 1: So we've seen a bunch of stars inside our galaxy

476
00:23:48,000 --> 00:23:50,879
Speaker 1: that have crazy high velocities like this one called S

477
00:23:50,960 --> 00:23:55,480
Speaker 1: five hbs one moving almost two thousand kilometers per second

478
00:23:55,600 --> 00:23:57,919
Speaker 1: relative to the center of the galaxy, and if you

479
00:23:57,920 --> 00:24:00,159
Speaker 1: look at its trajectory, it looks like it visited the

480
00:24:00,200 --> 00:24:03,439
Speaker 1: galactic center, got boosted by something in there, and is

481
00:24:03,440 --> 00:24:05,720
Speaker 1: now headed straight out of the galaxy.

482
00:24:06,000 --> 00:24:07,360
Speaker 2: Is it going to stop.

483
00:24:07,200 --> 00:24:09,600
Speaker 1: Unless it gets deflected by something else along the way?

484
00:24:09,640 --> 00:24:11,400
Speaker 1: It's moving out and we just hope that it writes

485
00:24:11,400 --> 00:24:13,200
Speaker 1: this letters and updates us on its life.

486
00:24:13,520 --> 00:24:16,760
Speaker 2: But it's just going to keep going and going and going.

487
00:24:16,760 --> 00:24:20,080
Speaker 2: And oh man, sorry, yeah, because the galaxy is pretty sparse,

488
00:24:20,200 --> 00:24:22,960
Speaker 2: especially once you leave the center, and so it's not

489
00:24:23,160 --> 00:24:24,720
Speaker 2: easy to like hit another star.

490
00:24:24,800 --> 00:24:26,879
Speaker 1: I mean, there's going to be gravitational deflections, but this

491
00:24:26,920 --> 00:24:28,280
Speaker 1: thing is moving super fast.

492
00:24:28,520 --> 00:24:28,800
Speaker 2: Wow.

493
00:24:28,840 --> 00:24:31,520
Speaker 1: Another way you can get a hypervelocity star is being

494
00:24:31,600 --> 00:24:34,159
Speaker 1: kicked by a supernova. So, for example, if you have

495
00:24:34,200 --> 00:24:37,960
Speaker 1: a binary star system, two stars formed together burning near

496
00:24:38,000 --> 00:24:40,720
Speaker 1: each other, if one of them becomes a supernova, which

497
00:24:40,720 --> 00:24:43,720
Speaker 1: happens sometimes if it's like not enough mass to become

498
00:24:43,760 --> 00:24:46,000
Speaker 1: a supernova and it becomes a white dwarf and then

499
00:24:46,119 --> 00:24:48,960
Speaker 1: later it gathers a little bit of extra mass, sometimes

500
00:24:49,040 --> 00:24:52,040
Speaker 1: from its partner. Then it can suddenly go supernova. That's

501
00:24:52,040 --> 00:24:54,960
Speaker 1: the type one A supernova, and that boost can kick

502
00:24:55,040 --> 00:24:58,480
Speaker 1: the other star out of the galaxy. And we've seen

503
00:24:58,520 --> 00:25:00,920
Speaker 1: one of these things. It's called U seven oh eight,

504
00:25:01,040 --> 00:25:04,840
Speaker 1: a helium rich subdwarf star moving super fast more than

505
00:25:04,840 --> 00:25:08,479
Speaker 1: a thousand kilometers per second, probably ejected by type one

506
00:25:08,520 --> 00:25:11,720
Speaker 1: A supernova. It's essentially it's partner. So that's like a

507
00:25:11,760 --> 00:25:12,560
Speaker 1: star divorce.

508
00:25:12,840 --> 00:25:17,480
Speaker 2: Oh ooh, And divorces are rarely clean and nice things,

509
00:25:17,560 --> 00:25:19,680
Speaker 2: but sometimes they are. But so it was super and ova.

510
00:25:19,720 --> 00:25:22,320
Speaker 2: That's just like a giant explosion, right, So the explosion

511
00:25:22,400 --> 00:25:23,639
Speaker 2: scent it flying, Yeah.

512
00:25:23,560 --> 00:25:26,040
Speaker 1: Exactly, it's a huge explosion. Really, this is an enormous

513
00:25:26,040 --> 00:25:29,359
Speaker 1: amount of energy. These stars are briefly brighter than the

514
00:25:29,400 --> 00:25:33,080
Speaker 1: rest of the galaxy combined. Wow, it's really a mind

515
00:25:33,119 --> 00:25:36,320
Speaker 1: boggling amount of energy, and all that radiation pressure can

516
00:25:36,359 --> 00:25:38,720
Speaker 1: push the other star and send it out of the

517
00:25:38,720 --> 00:25:42,560
Speaker 1: community to its lonely divorced data apartment. It's not me,

518
00:25:43,000 --> 00:25:49,880
Speaker 1: it's you, exactly. So the Doppler technique is the way

519
00:25:49,880 --> 00:25:52,400
Speaker 1: we measure these things, and so you can look around

520
00:25:52,520 --> 00:25:55,160
Speaker 1: and try to measure the speeds. But sometimes we can't

521
00:25:55,200 --> 00:25:57,760
Speaker 1: even measure these speeds very well. We can only sort

522
00:25:57,800 --> 00:25:59,000
Speaker 1: of find a minimum.

523
00:25:59,040 --> 00:26:00,920
Speaker 2: Why why is it so hard to measure the speed

524
00:26:00,960 --> 00:26:03,080
Speaker 2: is because they're so far away and moving so fast.

525
00:26:03,359 --> 00:26:04,919
Speaker 2: I mean, it's amazing we can measure any of this

526
00:26:04,920 --> 00:26:05,880
Speaker 2: stuff at all, to be.

527
00:26:05,840 --> 00:26:08,399
Speaker 1: Fair, Yeah, well, we can essentially only measure the speed

528
00:26:08,520 --> 00:26:10,960
Speaker 1: away from us, right, And so a star is moving

529
00:26:11,000 --> 00:26:14,080
Speaker 1: at an angle, then it has an additional velocity that

530
00:26:14,119 --> 00:26:16,840
Speaker 1: we're not capturing. OK, so this is sort of a

531
00:26:16,880 --> 00:26:17,760
Speaker 1: minimum speed.

532
00:26:17,960 --> 00:26:18,200
Speaker 2: Cool.

533
00:26:18,240 --> 00:26:20,840
Speaker 1: We have theories for how this might happen. Et. People

534
00:26:20,880 --> 00:26:23,480
Speaker 1: have been looking for these stars, and some astronomers from

535
00:26:23,520 --> 00:26:27,280
Speaker 1: Vanderbilt identified more than six hundred and seventy stars at

536
00:26:27,280 --> 00:26:29,679
Speaker 1: the edge of the Milky Way, sort of between us

537
00:26:29,720 --> 00:26:33,280
Speaker 1: and Andromeda. And these are stars that have already been ejected.

538
00:26:33,280 --> 00:26:35,919
Speaker 1: They're like living out there in the middle of space.

539
00:26:36,240 --> 00:26:38,399
Speaker 1: These are not stars that we're projecting are going to

540
00:26:38,480 --> 00:26:41,080
Speaker 1: leave the galaxy. They're just like out there floating in

541
00:26:41,080 --> 00:26:43,400
Speaker 1: the middle between us and the next galaxy.

542
00:26:43,520 --> 00:26:46,760
Speaker 2: Wow, and they must all be incredibly far away.

543
00:26:46,640 --> 00:26:49,439
Speaker 1: Yeah, exactly. These are far away stars. They're hard to see,

544
00:26:49,600 --> 00:26:51,800
Speaker 1: but the light that comes from them also tells us

545
00:26:51,840 --> 00:26:55,159
Speaker 1: about their origin. These stars are red giant stars. They

546
00:26:55,160 --> 00:26:57,440
Speaker 1: have a lot of metal in them, and it's hard

547
00:26:57,480 --> 00:27:00,639
Speaker 1: to find metals in between. Galaxiest tend to be at

548
00:27:00,640 --> 00:27:03,440
Speaker 1: the core, where there's a lot of gravity. There's more

549
00:27:03,480 --> 00:27:05,520
Speaker 1: metals at the center of the gravity than there are

550
00:27:05,720 --> 00:27:08,000
Speaker 1: in our neighborhood of the galaxy, and there's even less

551
00:27:08,040 --> 00:27:10,480
Speaker 1: in the outskirts of the galaxy. So the fact that

552
00:27:10,520 --> 00:27:12,639
Speaker 1: these stars have a lot of metal in them tells

553
00:27:12,720 --> 00:27:15,359
Speaker 1: us that they're probably formed close to the center of

554
00:27:15,400 --> 00:27:18,560
Speaker 1: a galaxy. These are definitely not formed out there in space.

555
00:27:18,920 --> 00:27:21,439
Speaker 1: So this is like direct confirmation of this whole idea

556
00:27:21,560 --> 00:27:24,840
Speaker 1: that stars are formed in galaxies and then sometimes ejected,

557
00:27:24,960 --> 00:27:27,400
Speaker 1: especially from the core, out into space.

558
00:27:27,720 --> 00:27:29,439
Speaker 2: Man, it's got to be hard to go from the

559
00:27:29,480 --> 00:27:32,520
Speaker 2: center of the universe to us to getting thrown out

560
00:27:32,520 --> 00:27:33,080
Speaker 2: on your own.

561
00:27:34,520 --> 00:27:35,400
Speaker 1: Yeah, exactly.

562
00:27:35,800 --> 00:27:37,600
Speaker 2: So I was really having fun when we were talking

563
00:27:37,600 --> 00:27:41,439
Speaker 2: about explosions. Are there any more explosion based ways that

564
00:27:41,520 --> 00:27:43,400
Speaker 2: stars can go rogue?

565
00:27:43,480 --> 00:27:46,800
Speaker 1: Sometimes stars go rogue and then they explode. This is

566
00:27:46,800 --> 00:27:51,880
Speaker 1: super awesome. It's an intergalactic supernova. So imagine the scenario

567
00:27:51,880 --> 00:27:53,639
Speaker 1: we had before. We have like a white dwarf and

568
00:27:53,680 --> 00:27:56,520
Speaker 1: a partner star, And earlier we talked about that white

569
00:27:56,560 --> 00:27:59,720
Speaker 1: dwarf exploding and kicking its partner out of the galaxy,

570
00:27:59,760 --> 00:28:02,200
Speaker 1: which seems unfair, but hey, it happens. It's a cold

571
00:28:02,280 --> 00:28:05,720
Speaker 1: universe out there. But sometimes those two stars get kicked

572
00:28:05,720 --> 00:28:09,840
Speaker 1: out together by something else. Maybe they together visited the

573
00:28:09,840 --> 00:28:12,560
Speaker 1: core of the galaxy and get ejected. Now they're out

574
00:28:12,600 --> 00:28:16,399
Speaker 1: there in the middle space between galaxies, and they're still

575
00:28:16,400 --> 00:28:19,000
Speaker 1: doing their thing, and then one of them can go

576
00:28:19,080 --> 00:28:22,399
Speaker 1: supernova by grabbing some of the material from the other one,

577
00:28:22,840 --> 00:28:25,280
Speaker 1: and so they can create an explosion out there in

578
00:28:25,320 --> 00:28:27,000
Speaker 1: the middle of space.

579
00:28:26,920 --> 00:28:31,320
Speaker 2: And that blows both of them, like out farther or

580
00:28:31,359 --> 00:28:32,000
Speaker 2: just one of them.

581
00:28:32,119 --> 00:28:33,960
Speaker 1: So then the other one, if it survives. They don't

582
00:28:34,000 --> 00:28:36,439
Speaker 1: always survive, but if it does, it'll get ejected in

583
00:28:36,480 --> 00:28:39,840
Speaker 1: some new direction. Right, So it's already got thrown out

584
00:28:39,840 --> 00:28:42,360
Speaker 1: by the galaxy, and now it's partners rejecting it and

585
00:28:42,400 --> 00:28:44,800
Speaker 1: it's getting shot out in some new direction. Yeah.

586
00:28:44,920 --> 00:28:47,360
Speaker 2: How could you possibly know that things had taken such

587
00:28:47,400 --> 00:28:51,200
Speaker 2: a complicated path without observing that directly. That's amazing.

588
00:28:51,600 --> 00:28:53,720
Speaker 1: It's hard to explain how you might get a supernova

589
00:28:53,800 --> 00:28:57,560
Speaker 1: otherwise in between galaxies, whether it just isn't the material

590
00:28:57,600 --> 00:28:58,600
Speaker 1: to form these stars.

591
00:28:58,800 --> 00:29:02,440
Speaker 2: Wow, So how many of these are there? Do we think?

592
00:29:02,720 --> 00:29:05,080
Speaker 1: So it's a great question. We've seen a lot of them,

593
00:29:05,120 --> 00:29:09,080
Speaker 1: like hundreds thousands by now of these intergalactic stars, these

594
00:29:09,200 --> 00:29:11,960
Speaker 1: rogue stars floating out there, and we're confident that they

595
00:29:12,040 --> 00:29:14,120
Speaker 1: come from galaxies. And then we take this step that

596
00:29:14,160 --> 00:29:17,000
Speaker 1: astronomers often do, which is try to estimate how many

597
00:29:17,000 --> 00:29:19,680
Speaker 1: of them are there, Like we're seeing a small number

598
00:29:19,720 --> 00:29:22,680
Speaker 1: of them, but we can also estimate our ability to

599
00:29:22,880 --> 00:29:25,200
Speaker 1: see them, Like if we think we're seeing only one

600
00:29:25,240 --> 00:29:28,040
Speaker 1: percent of the stuff that's out there because it's blocked

601
00:29:28,080 --> 00:29:30,920
Speaker 1: by something or because of our detection capabilities, that we

602
00:29:30,920 --> 00:29:33,280
Speaker 1: can count the number we see and extrapolate to the

603
00:29:33,320 --> 00:29:37,000
Speaker 1: total population. That's always a bit of a dangerous extrapolation

604
00:29:37,080 --> 00:29:39,760
Speaker 1: because you never really know what fraction of stuff are

605
00:29:39,760 --> 00:29:42,400
Speaker 1: you seeing because you don't see the whole denominator. But

606
00:29:42,560 --> 00:29:45,320
Speaker 1: you can use models and theories, et cetera. So this

607
00:29:45,400 --> 00:29:48,360
Speaker 1: is very speculative and there's lots of different estimates. Some

608
00:29:48,560 --> 00:29:51,880
Speaker 1: early estimates suggested that ten to twenty percent of all

609
00:29:52,000 --> 00:29:55,720
Speaker 1: stars in galactic clusters are not in a galaxy. That

610
00:29:55,760 --> 00:29:58,760
Speaker 1: they're between galaxies. Yeah, like one in five.

611
00:29:59,000 --> 00:30:01,160
Speaker 2: That's way higher than and I would have guessed. I

612
00:30:01,160 --> 00:30:03,040
Speaker 2: don't know why that seemed like a rare thing.

613
00:30:03,400 --> 00:30:05,080
Speaker 1: It seems like it should be a rare thing. On

614
00:30:05,120 --> 00:30:07,959
Speaker 1: the other hand, I think we're biased because of our experience.

615
00:30:08,040 --> 00:30:10,320
Speaker 1: We tend to think of our star and our planets

616
00:30:10,320 --> 00:30:13,280
Speaker 1: and our galaxy is the typical thing. But we've learned

617
00:30:13,280 --> 00:30:16,320
Speaker 1: over and over in physics that our experience is not typical.

618
00:30:16,440 --> 00:30:19,960
Speaker 1: Our kind of matter isn't typical, our star isn't typical,

619
00:30:20,440 --> 00:30:23,040
Speaker 1: and so this is just another example. And then I

620
00:30:23,080 --> 00:30:25,840
Speaker 1: read a more recent study that suggested maybe up to

621
00:30:26,000 --> 00:30:30,480
Speaker 1: fifty percent of all stars are not in galaxies. This

622
00:30:30,560 --> 00:30:32,760
Speaker 1: is much more speculative, and it came from understanding the

623
00:30:32,800 --> 00:30:35,960
Speaker 1: extra galactic background light, which is just like an overall

624
00:30:36,160 --> 00:30:39,560
Speaker 1: general glow of light that comes from outside the galaxy

625
00:30:39,560 --> 00:30:42,720
Speaker 1: that we don't fully understand and could be coming from

626
00:30:43,120 --> 00:30:47,000
Speaker 1: tons and tons of these hypervelocity rogue stars. But it's

627
00:30:47,080 --> 00:30:50,440
Speaker 1: very indirect and speculative. So the bottom line is it's

628
00:30:50,480 --> 00:30:53,960
Speaker 1: a big number rogue stars are out there. They're not rare.

629
00:30:54,120 --> 00:30:56,400
Speaker 1: We don't know what fraction of stars in the universe

630
00:30:56,400 --> 00:30:58,760
Speaker 1: are rogue. It might be ten percent, might be twenty percent,

631
00:30:58,840 --> 00:31:02,400
Speaker 1: might be fifty percent. It's some huge fraction of the

632
00:31:02,440 --> 00:31:05,120
Speaker 1: stuff that's out there in the universe. It's not unusual.

633
00:31:05,440 --> 00:31:08,440
Speaker 2: So from a sci fi perspective, whenever I hear about

634
00:31:08,480 --> 00:31:11,200
Speaker 2: dice and spheres, I think, what right do you have

635
00:31:11,400 --> 00:31:13,520
Speaker 2: to take all of the light from the Sun and

636
00:31:13,560 --> 00:31:17,040
Speaker 2: deprive all the planets that rely on that light? You know,

637
00:31:17,200 --> 00:31:19,560
Speaker 2: of the Sun's light. But if fifty percent of the

638
00:31:19,600 --> 00:31:22,600
Speaker 2: suns out there, yeah, don't have any planets around them.

639
00:31:22,800 --> 00:31:25,200
Speaker 2: We could just go and capture that energy. And what

640
00:31:25,280 --> 00:31:26,080
Speaker 2: does that harm?

641
00:31:26,520 --> 00:31:28,560
Speaker 1: Well, that's a great question. Actually, if a star is

642
00:31:28,600 --> 00:31:32,760
Speaker 1: ejected from the galaxy, does it keep its planets or not? Right,

643
00:31:33,400 --> 00:31:36,360
Speaker 1: because I think you're assuming that a star that undergoes

644
00:31:36,360 --> 00:31:39,200
Speaker 1: that kind of gravitational perturbation is going to lose its planets,

645
00:31:39,480 --> 00:31:42,920
Speaker 1: And I think that's probably true, but not necessarily right.

646
00:31:42,960 --> 00:31:45,440
Speaker 1: If you think about the whole Solar System as an object,

647
00:31:45,760 --> 00:31:48,320
Speaker 1: it basically gets the same gravity, and so like the

648
00:31:48,360 --> 00:31:50,240
Speaker 1: forces on the star are the same as the forces

649
00:31:50,240 --> 00:31:53,479
Speaker 1: on the planets. Depends in detail and how close it

650
00:31:53,520 --> 00:31:56,000
Speaker 1: comes to that super massive black hole, does it feel

651
00:31:56,080 --> 00:31:58,880
Speaker 1: tidal forces is that black hole pulling the whole Solar

652
00:31:58,960 --> 00:32:02,320
Speaker 1: system apart or pushing on the entire thing together? Does

653
00:32:02,360 --> 00:32:05,080
Speaker 1: the star have enough gravity to hang on to its planets?

654
00:32:05,200 --> 00:32:08,000
Speaker 2: Okay, so you're saying that, like some of the things

655
00:32:08,000 --> 00:32:10,360
Speaker 2: that we've just talked about, when the Sun gets ejected,

656
00:32:10,840 --> 00:32:13,400
Speaker 2: it brings its planets with it, and it forms a

657
00:32:13,400 --> 00:32:15,240
Speaker 2: solar system in a new place.

658
00:32:15,520 --> 00:32:17,560
Speaker 1: I think that's possible. I think it's more likely that

659
00:32:17,640 --> 00:32:20,840
Speaker 1: they lose it because of the crazy physics involved, but

660
00:32:20,920 --> 00:32:24,080
Speaker 1: it's not guaranteed. So some of those rogue stars probably

661
00:32:24,080 --> 00:32:26,600
Speaker 1: do have planets, So hold off on stealing all of

662
00:32:26,640 --> 00:32:27,840
Speaker 1: their energy, please, Kelly.

663
00:32:27,960 --> 00:32:30,840
Speaker 2: Well, you know that I'm a skeptic in all things,

664
00:32:31,200 --> 00:32:35,120
Speaker 2: so I don't suspect this will come up soon, but

665
00:32:35,280 --> 00:32:36,840
Speaker 2: you know I would caution people to see if there

666
00:32:36,840 --> 00:32:39,120
Speaker 2: are planets before you steal a sun's energy.

667
00:32:39,720 --> 00:32:42,320
Speaker 1: Like a good policy. All Right, So let's take a

668
00:32:42,320 --> 00:32:44,960
Speaker 1: break and we come back. We'll talk about rogue planets

669
00:32:45,000 --> 00:32:47,960
Speaker 1: out there without a galaxy or even without a star.

670
00:33:07,920 --> 00:33:10,520
Speaker 2: All Right, we're back and we're talking about rogue planets.

671
00:33:10,560 --> 00:33:12,400
Speaker 2: And so, just to clarify, you were telling us a

672
00:33:12,400 --> 00:33:15,400
Speaker 2: moment ago that suns can get ejected, and sometimes they

673
00:33:15,400 --> 00:33:16,640
Speaker 2: take their planets with them.

674
00:33:16,920 --> 00:33:20,080
Speaker 1: We've never seen that because it's hard to see exoplanets,

675
00:33:20,160 --> 00:33:23,200
Speaker 1: especially for really distant stars and the higher velocity stars

676
00:33:23,200 --> 00:33:26,920
Speaker 1: we've seen. We've never identified an exoplanet on a hypervelocity star,

677
00:33:27,120 --> 00:33:28,000
Speaker 1: but it is possible.

678
00:33:28,200 --> 00:33:30,640
Speaker 2: Okay, But when we were talking about rogue planets, now

679
00:33:30,960 --> 00:33:33,960
Speaker 2: we're not talking about planets that got pulled with their star.

680
00:33:34,040 --> 00:33:37,080
Speaker 2: We're talking about planets that got pushed away from their

681
00:33:37,080 --> 00:33:38,840
Speaker 2: star and now they're all out on their own. Is

682
00:33:38,880 --> 00:33:39,200
Speaker 2: that right?

683
00:33:39,360 --> 00:33:41,760
Speaker 1: Yeah, exactly, So a rogue planet would be a planet

684
00:33:41,800 --> 00:33:44,920
Speaker 1: inside the galaxy still, oh, but without a star to

685
00:33:44,960 --> 00:33:48,840
Speaker 1: call home, right, because the galaxy is mostly empty. I me,

686
00:33:49,000 --> 00:33:50,680
Speaker 1: it looks pretty bright when you look up at the

687
00:33:50,720 --> 00:33:52,800
Speaker 1: stars at night and you can see the Milky Way,

688
00:33:52,840 --> 00:33:54,840
Speaker 1: and there are lots and lots of stars out there,

689
00:33:55,320 --> 00:33:58,360
Speaker 1: but most places in the galaxy are pretty far from

690
00:33:58,400 --> 00:34:01,480
Speaker 1: any star. If you get like randomly dropped into a

691
00:34:01,520 --> 00:34:04,120
Speaker 1: spot in the galaxy, the odds are you're not close

692
00:34:04,160 --> 00:34:06,880
Speaker 1: to any star. That mostly you just see like distant

693
00:34:06,920 --> 00:34:10,720
Speaker 1: stars around you. But you wouldn't consider yourself gravitationally bound

694
00:34:11,120 --> 00:34:12,479
Speaker 1: or held by any star.

695
00:34:12,760 --> 00:34:13,959
Speaker 2: But there'd probably be gas.

696
00:34:14,480 --> 00:34:16,480
Speaker 1: The gas is always gas.

697
00:34:16,800 --> 00:34:19,320
Speaker 2: There's always gas. The one constant in life is gas

698
00:34:19,640 --> 00:34:20,360
Speaker 2: and radiation.

699
00:34:20,520 --> 00:34:23,200
Speaker 1: And so think of these planets as like having the

700
00:34:23,200 --> 00:34:26,040
Speaker 1: same relationship with the galaxy as our sun does. Right

701
00:34:26,080 --> 00:34:28,200
Speaker 1: the Sun orbits the center of the galaxy, you could

702
00:34:28,200 --> 00:34:30,960
Speaker 1: also have a planet out there orbiting the center of

703
00:34:31,000 --> 00:34:34,239
Speaker 1: the galaxy, not necessarily orbiting a star directly. So that's

704
00:34:34,239 --> 00:34:35,800
Speaker 1: what we would call a rogue planet.

705
00:34:36,000 --> 00:34:37,840
Speaker 2: So how do you get rogue planets?

706
00:34:37,840 --> 00:34:38,040
Speaker 4: Then?

707
00:34:38,400 --> 00:34:40,319
Speaker 1: So it's sort of the same process we talked about

708
00:34:40,320 --> 00:34:43,920
Speaker 1: for stars, but in miniature, like if two solar systems

709
00:34:43,960 --> 00:34:46,640
Speaker 1: come near each other, then the stars can tug on

710
00:34:46,680 --> 00:34:50,439
Speaker 1: each other's planets and cause gravitational instability. Our orbit around

711
00:34:50,480 --> 00:34:53,719
Speaker 1: the star is pretty stable. Like a little perturbation, we'll

712
00:34:53,719 --> 00:34:55,880
Speaker 1: go back to our orbit, but it's not that stable.

713
00:34:55,960 --> 00:34:57,800
Speaker 1: You give it a big enough push, we get the

714
00:34:57,840 --> 00:35:01,080
Speaker 1: wrong direction. We are flying out of this solar system,

715
00:35:01,360 --> 00:35:03,759
Speaker 1: and so it's certainly possible that a visitor can come

716
00:35:03,800 --> 00:35:06,359
Speaker 1: and perturb our solar system and we could end up

717
00:35:06,400 --> 00:35:07,400
Speaker 1: losing a planet.

718
00:35:07,560 --> 00:35:10,399
Speaker 2: There's the existential dreadf come to expect from a white

719
00:35:10,400 --> 00:35:12,480
Speaker 2: Sun episode. Glad we got.

720
00:35:12,239 --> 00:35:17,160
Speaker 1: There, And also sometimes the planets form, and it's pretty chaotic.

721
00:35:17,239 --> 00:35:19,760
Speaker 1: Like we think of the Solar system as very stable

722
00:35:20,040 --> 00:35:22,960
Speaker 1: and chill. Everybody's driving around the star is staying in

723
00:35:23,000 --> 00:35:25,319
Speaker 1: their lane. But you know, this is billions of years

724
00:35:25,360 --> 00:35:28,000
Speaker 1: along and earlier on there was a lot of chaos.

725
00:35:28,400 --> 00:35:31,359
Speaker 1: As the planets formed. They gravitationally interact with each other,

726
00:35:31,400 --> 00:35:33,680
Speaker 1: and any system that has more than two objects in

727
00:35:33,760 --> 00:35:37,040
Speaker 1: it is chaotic and hard to predict. We had like

728
00:35:37,120 --> 00:35:41,840
Speaker 1: Saturn and Jupiter and we think another major gas giant

729
00:35:41,920 --> 00:35:45,640
Speaker 1: in our Solar system. And then Jupiter and Saturn moved

730
00:35:45,680 --> 00:35:48,080
Speaker 1: in towards the center of the Solar system and then

731
00:35:48,120 --> 00:35:50,640
Speaker 1: they got tugged by the other planet and Jupiter and

732
00:35:50,680 --> 00:35:53,560
Speaker 1: Saturn came back out, so they didn't like fall into

733
00:35:53,560 --> 00:35:56,960
Speaker 1: the Sun, but the other planet got ejected. And so

734
00:35:57,000 --> 00:35:59,960
Speaker 1: this can happen that you have this complicated interaction between

735
00:36:00,239 --> 00:36:03,960
Speaker 1: the planets, or sometimes a neighboring star can perturb things

736
00:36:04,200 --> 00:36:06,600
Speaker 1: and you get a lot of planets actually thrown out

737
00:36:06,600 --> 00:36:07,560
Speaker 1: of solar systems.

738
00:36:08,200 --> 00:36:11,160
Speaker 2: So this isn't just when solar systems are initially forming.

739
00:36:11,200 --> 00:36:12,920
Speaker 2: This could this could happen now.

740
00:36:13,320 --> 00:36:15,439
Speaker 1: You should be worrying about it right now, Kelly. In fact,

741
00:36:15,440 --> 00:36:17,400
Speaker 1: if you don't worry about it. It's more likely to happen.

742
00:36:17,960 --> 00:36:21,640
Speaker 2: Oh my gosh, kissing bugs. Planets getting ejected. It's a

743
00:36:21,680 --> 00:36:22,480
Speaker 2: scary world.

744
00:36:22,920 --> 00:36:25,360
Speaker 1: It mostly happens in the early days of a solar system,

745
00:36:25,360 --> 00:36:27,120
Speaker 1: but it could happen. Yeah, if we have another star

746
00:36:27,239 --> 00:36:30,040
Speaker 1: come and visit us really close, then absolutely you could

747
00:36:30,080 --> 00:36:33,040
Speaker 1: scramble our solar system. And we've done a bunch of

748
00:36:33,040 --> 00:36:37,120
Speaker 1: calculations and they suggest that like maybe twenty five to

749
00:36:37,160 --> 00:36:40,959
Speaker 1: fifty percent of planets that get formed get ejected from

750
00:36:41,040 --> 00:36:45,040
Speaker 1: stars what now exactly, which kind of makes sense because

751
00:36:45,080 --> 00:36:47,719
Speaker 1: it's not that easy to get everything arranged in the

752
00:36:47,800 --> 00:36:50,360
Speaker 1: right angles and velocities and distances to stay in a

753
00:36:50,360 --> 00:36:53,160
Speaker 1: stable orbit, especially when you've got other planets tugging on you.

754
00:36:53,320 --> 00:36:56,160
Speaker 2: And so do these planets tend to like get sucked

755
00:36:56,239 --> 00:37:00,839
Speaker 2: into other solar systems eventually or they're just off completely themselves.

756
00:37:01,080 --> 00:37:03,279
Speaker 1: They can be sucked into other solar systems, but a

757
00:37:03,320 --> 00:37:05,279
Speaker 1: lot of them are just off by themselves because the

758
00:37:05,320 --> 00:37:08,279
Speaker 1: galaxy is mostly empty. But yeah, you could end up

759
00:37:08,320 --> 00:37:10,920
Speaker 1: being captured by another solar system, or if you're a

760
00:37:10,960 --> 00:37:14,040
Speaker 1: tiny planet, you can join the like huge crowd of

761
00:37:14,280 --> 00:37:18,440
Speaker 1: frozen stuff. The outskirts of solar systems, right, So absolutely

762
00:37:18,480 --> 00:37:21,320
Speaker 1: this gonna happen. And for example, like those interstellar visitors

763
00:37:21,360 --> 00:37:23,480
Speaker 1: like Atlas and know Mua mua, I love the.

764
00:37:23,480 --> 00:37:25,879
Speaker 2: Way you always say that right the first time, which

765
00:37:25,920 --> 00:37:27,799
Speaker 2: is totally different than how I say it.

766
00:37:28,920 --> 00:37:31,279
Speaker 1: These things are demonstrations of how that works. Right. These

767
00:37:31,280 --> 00:37:35,280
Speaker 1: things were formed around another star and then gravitationally somehow

768
00:37:35,320 --> 00:37:38,480
Speaker 1: detached from that star, sent through space and now hitting

769
00:37:38,520 --> 00:37:41,080
Speaker 1: our Solar system. And it's unlikely that they're going to

770
00:37:41,160 --> 00:37:43,640
Speaker 1: get captured in our solar system and like join our neighborhood.

771
00:37:43,640 --> 00:37:45,640
Speaker 1: They're going to fly through and get sling shotted out

772
00:37:45,680 --> 00:37:48,600
Speaker 1: in some other direction. But there's stuff out there that's

773
00:37:48,600 --> 00:37:52,160
Speaker 1: formed by one solar system, ejected and now flying through space,

774
00:37:52,600 --> 00:37:55,480
Speaker 1: maybe interacting with other stars. And we think that there

775
00:37:55,520 --> 00:37:57,160
Speaker 1: are a lot of planets that are like this.

776
00:37:57,480 --> 00:37:59,440
Speaker 2: Is there any evidence that any of the planets in

777
00:37:59,480 --> 00:38:01,840
Speaker 2: our solar system we're thrown out of another one and

778
00:38:01,920 --> 00:38:02,680
Speaker 2: ended up in ours.

779
00:38:03,840 --> 00:38:05,880
Speaker 1: You're wondering if any planets are adopted.

780
00:38:06,040 --> 00:38:07,480
Speaker 2: That's right, we love adoption.

781
00:38:08,239 --> 00:38:10,360
Speaker 1: No, there's no evidence for that, and all the models

782
00:38:10,360 --> 00:38:13,000
Speaker 1: suggest that the planets we have were formed here, but

783
00:38:13,080 --> 00:38:15,240
Speaker 1: that there were some planets formed here that we've lost.

784
00:38:15,560 --> 00:38:17,200
Speaker 2: Okay, are there any other ways?

785
00:38:17,440 --> 00:38:19,880
Speaker 1: There are some other ways you might get a rogue planet.

786
00:38:19,920 --> 00:38:22,880
Speaker 1: For example, if you have a star that's forming, but

787
00:38:22,960 --> 00:38:25,960
Speaker 1: it's not enough mass to really have fusion, so it

788
00:38:25,960 --> 00:38:29,560
Speaker 1: becomes like a sub brown dwarf star. That's a star

789
00:38:29,680 --> 00:38:33,400
Speaker 1: that isn't hot enough at its core to ignite real fusion.

790
00:38:33,480 --> 00:38:36,120
Speaker 1: Sometimes you can get like a weaker version of fusion going.

791
00:38:36,320 --> 00:38:38,160
Speaker 1: But sometimes they're in the middle. There's sort of like

792
00:38:38,200 --> 00:38:41,640
Speaker 1: a super Jupiter, like a version of Jupiter that's really big,

793
00:38:41,680 --> 00:38:44,759
Speaker 1: bigger than Jupiter, smaller than what you need to get

794
00:38:44,800 --> 00:38:47,360
Speaker 1: fusion going. A lot to argument about whether this should

795
00:38:47,360 --> 00:38:49,680
Speaker 1: be called a rogue planet because it's not really like

796
00:38:49,719 --> 00:38:52,560
Speaker 1: a planet formed around a star and then ejected, or

797
00:38:52,600 --> 00:38:56,480
Speaker 1: like a failed star. So you know, astronomers argue about names.

798
00:38:56,719 --> 00:39:00,440
Speaker 2: Yeah, and those names carry baggage star.

799
00:39:01,400 --> 00:39:03,160
Speaker 1: Would you rather be a rogue or a failure?

800
00:39:03,320 --> 00:39:06,759
Speaker 2: Yeah, I'd rather be a rugue rogue obviously, Yeah, that's

801
00:39:06,800 --> 00:39:11,320
Speaker 2: way cooler. Rogue implies you chose this path, right exactly.

802
00:39:11,360 --> 00:39:13,640
Speaker 1: I was never trying to be a star anyway. Okay,

803
00:39:13,800 --> 00:39:18,480
Speaker 1: that's right, And these are things that we can see

804
00:39:18,560 --> 00:39:21,000
Speaker 1: out there in the galaxy. They're not nearly as far

805
00:39:21,040 --> 00:39:24,880
Speaker 1: away as the hypervelocity intergalactic stars that we talked about,

806
00:39:25,040 --> 00:39:27,160
Speaker 1: but they're harder to see because they're not bright. Right.

807
00:39:27,239 --> 00:39:31,120
Speaker 1: Stars emit light, so you can see distant stars pretty easily.

808
00:39:31,440 --> 00:39:33,719
Speaker 1: Planets don't emit visible light, but they do emit in

809
00:39:33,800 --> 00:39:36,400
Speaker 1: the infrared. Remember that everything that's out there in the

810
00:39:36,440 --> 00:39:38,840
Speaker 1: universe that has a temperature, which is everything except for

811
00:39:38,960 --> 00:39:42,680
Speaker 1: dark matter, glows at some frequency, and that frequency depends

812
00:39:42,719 --> 00:39:45,240
Speaker 1: on the temperature. So the hotter you are, the higher

813
00:39:45,239 --> 00:39:48,120
Speaker 1: the frequency. The colder you are, the lower the frequency.

814
00:39:48,160 --> 00:39:50,880
Speaker 1: So Earth glows, for example, in the infrared. If you

815
00:39:51,200 --> 00:39:53,400
Speaker 1: take night vision goggles, you can look down to the ground.

816
00:39:53,400 --> 00:39:56,640
Speaker 1: You can see light being emitted from the surface, just

817
00:39:56,680 --> 00:39:58,640
Speaker 1: the way you can see light emitted from another person,

818
00:39:58,680 --> 00:40:01,359
Speaker 1: and it's a different temperature, and that's how you can

819
00:40:01,400 --> 00:40:04,160
Speaker 1: see like people at night. Or that's how those thermometers

820
00:40:04,200 --> 00:40:06,600
Speaker 1: work that look at your forehead in deduce your temperature

821
00:40:06,600 --> 00:40:09,879
Speaker 1: without touching you. They're measuring the frequency of infrared light

822
00:40:09,960 --> 00:40:13,400
Speaker 1: and inverting that process to deduce what your temperature must be.

823
00:40:14,000 --> 00:40:18,080
Speaker 1: So we can directly see planets using infrared telescopes because

824
00:40:18,120 --> 00:40:21,480
Speaker 1: they glow in that particular wavelength. We can't use this

825
00:40:21,520 --> 00:40:24,200
Speaker 1: technique to see exoplanets because they're usually like drowned out

826
00:40:24,200 --> 00:40:27,520
Speaker 1: by their star. There is possible, but you can directly

827
00:40:27,600 --> 00:40:31,480
Speaker 1: image rogue planets using like the Wise infrared telescope to

828
00:40:31,600 --> 00:40:33,840
Speaker 1: see them in the IR, which is super cool.

829
00:40:34,080 --> 00:40:35,600
Speaker 2: That is super cool. Is that the only way we

830
00:40:35,640 --> 00:40:36,000
Speaker 2: see them.

831
00:40:36,120 --> 00:40:38,720
Speaker 1: No, the most more common way is to see micro lensing.

832
00:40:38,960 --> 00:40:41,239
Speaker 1: Like you're looking at a star out in space, and

833
00:40:41,239 --> 00:40:43,800
Speaker 1: they shouldn't twinkle right out in space, stars don't twinkle.

834
00:40:43,960 --> 00:40:46,920
Speaker 1: That's an atmospheric effect we have on the ground in

835
00:40:47,040 --> 00:40:49,640
Speaker 1: out in space, they shouldn't twinkle. But if something passes

836
00:40:49,680 --> 00:40:52,279
Speaker 1: between you and the star, like a little mini eclipse.

837
00:40:52,360 --> 00:40:55,880
Speaker 1: They call this micro lensing, then you can deduce if

838
00:40:55,880 --> 00:40:58,239
Speaker 1: there was something there, and so you can look out

839
00:40:58,239 --> 00:41:02,000
Speaker 1: into space and count how often like stars twinkle essentially,

840
00:41:02,120 --> 00:41:05,840
Speaker 1: and there's a project here called OGLE Optical Gravitational Lensing

841
00:41:05,880 --> 00:41:10,560
Speaker 1: Experiment awesome acronym GUYS, and another one MOA micro Lensing

842
00:41:10,600 --> 00:41:14,200
Speaker 1: Observations in astrophysics, and these things measure how often this happens,

843
00:41:14,320 --> 00:41:16,759
Speaker 1: and then they do that same inversion step. They're like well,

844
00:41:17,000 --> 00:41:19,799
Speaker 1: we see seventy four of these, how likely are we

845
00:41:19,880 --> 00:41:21,960
Speaker 1: to see one if it's out there? You know, what

846
00:41:22,000 --> 00:41:24,600
Speaker 1: are the chances that the star and the planet arrange

847
00:41:24,640 --> 00:41:27,560
Speaker 1: themselves in exactly the right way? And then they estimate

848
00:41:27,560 --> 00:41:29,520
Speaker 1: how many there are out there in the universe.

849
00:41:29,920 --> 00:41:34,080
Speaker 2: So, if you detect micro lensing, something has gotten the

850
00:41:34,120 --> 00:41:36,400
Speaker 2: way of your image, you've got a little eclipse going on.

851
00:41:36,440 --> 00:41:38,480
Speaker 2: How do you know that that's an exoplanet and not

852
00:41:38,640 --> 00:41:40,760
Speaker 2: like a big comet or something.

853
00:41:41,040 --> 00:41:43,160
Speaker 1: Yeah, it's a great question. Essentially, we could only see

854
00:41:43,200 --> 00:41:45,560
Speaker 1: this for bigger stuff. So like, what's the difference between

855
00:41:45,560 --> 00:41:48,719
Speaker 1: a big comet and a planet? Basically just the size, right.

856
00:41:48,760 --> 00:41:50,959
Speaker 1: A comet is just a chunk of rock and ice

857
00:41:51,080 --> 00:41:54,520
Speaker 1: anyway that's been ejected from a solar system. Like would

858
00:41:54,520 --> 00:41:58,520
Speaker 1: you call Omuamua or Atlas a comet or a planet?

859
00:41:58,560 --> 00:42:00,359
Speaker 1: We just call them a comet because they're not as

860
00:42:00,360 --> 00:42:02,600
Speaker 1: big as a planet. But we can only really see

861
00:42:02,680 --> 00:42:06,440
Speaker 1: stuff that's like Jupiter sized or a little bit smaller,

862
00:42:06,480 --> 00:42:09,479
Speaker 1: because otherwise it's too small to really eclipse the star.

863
00:42:09,719 --> 00:42:12,120
Speaker 1: This is really cool, but one time they saw a

864
00:42:12,239 --> 00:42:16,120
Speaker 1: Jupiter sized free floating planet and they think they saw

865
00:42:16,440 --> 00:42:19,879
Speaker 1: a moon around that planet. So this is like an

866
00:42:19,920 --> 00:42:22,200
Speaker 1: exo moon around a rogue planet.

867
00:42:22,360 --> 00:42:24,719
Speaker 2: Oh that's really cool. Yeah, I want of is it?

868
00:42:26,640 --> 00:42:28,160
Speaker 1: And this is due to like the pattern of the

869
00:42:28,200 --> 00:42:31,640
Speaker 1: eclipse as the lensing event happens. Right, it doesn't look

870
00:42:31,680 --> 00:42:33,920
Speaker 1: like just a sphere. It looks like a sphere plus

871
00:42:33,960 --> 00:42:36,879
Speaker 1: another sphere in order to model the pattern of the light.

872
00:42:37,400 --> 00:42:40,160
Speaker 1: Super cool, and we should see lots more of these.

873
00:42:40,280 --> 00:42:43,760
Speaker 1: The Nancy Grace Roman Space Telescope will measure the deflection

874
00:42:43,840 --> 00:42:47,640
Speaker 1: of background star's position to determine rogue planet masses. So

875
00:42:47,719 --> 00:42:50,800
Speaker 1: we have like a lot of observations of rogue planets

876
00:42:50,800 --> 00:42:53,400
Speaker 1: coming up in the future. But again, we think that

877
00:42:53,520 --> 00:42:56,839
Speaker 1: rogue planets are not rare. We think that probably the

878
00:42:56,840 --> 00:43:01,400
Speaker 1: Milky Way has billions of row planets, not like seven,

879
00:43:01,880 --> 00:43:06,000
Speaker 1: like forty two and not sixty five thousand, but billions

880
00:43:06,080 --> 00:43:07,080
Speaker 1: of rogue planets.

881
00:43:07,239 --> 00:43:09,160
Speaker 2: Wow, okay, and so all right, So now we've got

882
00:43:09,360 --> 00:43:13,280
Speaker 2: billions of data points as I imagine them out in space.

883
00:43:14,000 --> 00:43:17,719
Speaker 2: Are they easier to study or harder to study than

884
00:43:17,760 --> 00:43:19,880
Speaker 2: planets that are part of a solar system because I

885
00:43:19,880 --> 00:43:22,120
Speaker 2: imagine they're not being like drowned out by their sun

886
00:43:22,640 --> 00:43:25,200
Speaker 2: on the other hand, maybe some light from the sun

887
00:43:25,280 --> 00:43:27,440
Speaker 2: is helpful to view them. Like, how, yeah, tell me

888
00:43:27,480 --> 00:43:28,560
Speaker 2: about studying these guys.

889
00:43:28,719 --> 00:43:31,480
Speaker 1: Yeah, you basically nailed that. It's easier and harder. So

890
00:43:31,520 --> 00:43:33,960
Speaker 1: it's easier in some ways because they're not drowned out

891
00:43:33,960 --> 00:43:36,120
Speaker 1: by their star, but it's harder because that star can

892
00:43:36,239 --> 00:43:39,400
Speaker 1: illuminate them. Like some studies we do in exoplanets require

893
00:43:39,440 --> 00:43:42,080
Speaker 1: the light from that star. We can, for example, measure

894
00:43:42,120 --> 00:43:44,440
Speaker 1: that light going through that planet's atmosphere and then use

895
00:43:44,480 --> 00:43:47,279
Speaker 1: that to detect what's in the atmosphere that star by

896
00:43:47,520 --> 00:43:50,400
Speaker 1: which light's been absorbed and which light has not been absorbed.

897
00:43:50,560 --> 00:43:52,160
Speaker 1: So that's a cool study you can do on an

898
00:43:52,200 --> 00:43:54,839
Speaker 1: exoplanet around another star that you couldn't do on an

899
00:43:54,880 --> 00:43:58,319
Speaker 1: exo rogue planet. But exoogue planets you can see there

900
00:43:58,320 --> 00:44:00,759
Speaker 1: infrared light directly, which means you can do things like

901
00:44:01,200 --> 00:44:04,719
Speaker 1: measure the surface temperature of that planet, you know, and

902
00:44:04,840 --> 00:44:07,800
Speaker 1: understand what light it's emitting and all sorts of cool stuff.

903
00:44:08,239 --> 00:44:10,320
Speaker 1: So yeah, you can do different kinds of science.

904
00:44:10,600 --> 00:44:13,040
Speaker 2: Amazing. So what other kinds of science can we do

905
00:44:13,120 --> 00:44:15,120
Speaker 2: now that we figured out that there are rogue planets

906
00:44:15,120 --> 00:44:16,320
Speaker 2: and rogue stars.

907
00:44:16,239 --> 00:44:18,920
Speaker 1: Well, it really helps inform our model of solar system

908
00:44:19,000 --> 00:44:22,240
Speaker 1: formation and galactic formation right to understand how this happens.

909
00:44:22,280 --> 00:44:24,840
Speaker 1: Because our models should predict this, then we should go

910
00:44:24,880 --> 00:44:27,000
Speaker 1: out and check it and see that we see the

911
00:44:27,080 --> 00:44:30,320
Speaker 1: number of planets and stars that we are expecting. I remember,

912
00:44:30,320 --> 00:44:32,600
Speaker 1: there's still a lot of uncertainty because a lot of

913
00:44:32,640 --> 00:44:35,879
Speaker 1: the steps here do have direct observation to support them,

914
00:44:36,040 --> 00:44:39,200
Speaker 1: but some of them have some extrapolation that relies on models, right,

915
00:44:39,280 --> 00:44:41,680
Speaker 1: like what fraction of these things should we see? And

916
00:44:41,719 --> 00:44:44,160
Speaker 1: so you know, over the next few years we'll get

917
00:44:44,200 --> 00:44:46,480
Speaker 1: better and better and these estimates will are firmer and firmer.

918
00:44:46,520 --> 00:44:48,680
Speaker 1: But I think we can be confident in the bottom

919
00:44:48,719 --> 00:44:50,239
Speaker 1: line that there are a lot of them.

920
00:44:50,719 --> 00:44:53,680
Speaker 2: By the time this episode comes out, everybody should have

921
00:44:53,840 --> 00:44:57,960
Speaker 2: their physical copy of Do Aliens Speak Physics in their hands,

922
00:44:58,080 --> 00:44:59,840
Speaker 2: and they would have had at least a month to

923
00:45:00,600 --> 00:45:02,759
Speaker 2: And so I'm sure that you are all dreaming about

924
00:45:02,800 --> 00:45:05,879
Speaker 2: aliens as much as I have been since reading the book,

925
00:45:05,920 --> 00:45:09,640
Speaker 2: and so you're probably wondering could life evolve on roadue

926
00:45:09,640 --> 00:45:11,839
Speaker 2: planets and what would it be like? And could they

927
00:45:11,880 --> 00:45:15,560
Speaker 2: communicate with us? So, Daniel, is their life on road planets?

928
00:45:15,800 --> 00:45:18,439
Speaker 1: I certainly hope so, because it would provide the kind

929
00:45:18,520 --> 00:45:21,800
Speaker 1: of alternative aliens that I like thinking about in that book.

930
00:45:21,840 --> 00:45:23,759
Speaker 1: You know, ways that aliens might have evolved that are

931
00:45:23,840 --> 00:45:26,560
Speaker 1: very different from ours, that would lead them to explore

932
00:45:26,600 --> 00:45:30,160
Speaker 1: and understand the universe very differently. Like imagine evolving on

933
00:45:30,200 --> 00:45:32,759
Speaker 1: a planet like that. You have no seasons, you have

934
00:45:32,800 --> 00:45:35,919
Speaker 1: no days, right, because all these things require a star.

935
00:45:36,480 --> 00:45:39,759
Speaker 1: The surface is going to be extraordinarily cold. The atmosphere

936
00:45:40,040 --> 00:45:42,759
Speaker 1: might be snow. It just might freeze and fall to

937
00:45:42,800 --> 00:45:46,200
Speaker 1: the surface. The whole top mile of an ocean could

938
00:45:46,200 --> 00:45:49,279
Speaker 1: be frozen. So you're more likely to evolve, you know,

939
00:45:49,520 --> 00:45:52,719
Speaker 1: underneath a very frozen ocean, if you're kept warm by

940
00:45:52,760 --> 00:45:57,000
Speaker 1: like the internal geothermal of that planet. You know, on Earth,

941
00:45:57,280 --> 00:45:59,920
Speaker 1: something like ninety nine point seven percent of our energy

942
00:46:00,080 --> 00:46:03,560
Speaker 1: comes from the Sun, and so it'd be very difficult

943
00:46:03,600 --> 00:46:05,759
Speaker 1: to evolve in that scenario. But if you do, you'd

944
00:46:05,800 --> 00:46:08,720
Speaker 1: have a unique perspective on the universe. For sure.

945
00:46:09,040 --> 00:46:12,040
Speaker 2: It is really good to live on Earth, which I

946
00:46:12,040 --> 00:46:13,799
Speaker 2: think is the message that we come to at the

947
00:46:13,880 --> 00:46:16,360
Speaker 2: end of almost every episode where we talk about space.

948
00:46:17,440 --> 00:46:19,560
Speaker 2: It is pretty solid to be right here.

949
00:46:19,920 --> 00:46:21,799
Speaker 1: It is. I love that we get to live on Earth.

950
00:46:21,800 --> 00:46:24,160
Speaker 1: It's a pretty cushy place to evolve. But I hope

951
00:46:24,160 --> 00:46:26,000
Speaker 1: the aliens are out there and they had a very

952
00:46:26,040 --> 00:46:29,759
Speaker 1: weird experience, because talking to scientists from that planet could

953
00:46:29,760 --> 00:46:32,960
Speaker 1: give us a very different view on how the universe works.

954
00:46:33,000 --> 00:46:35,239
Speaker 1: You know, if you evolve on a rogue planet, maybe

955
00:46:35,280 --> 00:46:37,759
Speaker 1: you're not interested in stars and you haven't focused on

956
00:46:37,880 --> 00:46:39,759
Speaker 1: solar systems, and you have a very different way of

957
00:46:39,840 --> 00:46:42,479
Speaker 1: seeing the universe and the galaxy. Maybe you don't break

958
00:46:42,520 --> 00:46:44,279
Speaker 1: it up into the same units we do, and so

959
00:46:44,360 --> 00:46:48,400
Speaker 1: you've come up with alternative explanations or gone down different paths,

960
00:46:48,400 --> 00:46:51,640
Speaker 1: which of course could just inform our joint understanding of

961
00:46:51,640 --> 00:46:52,240
Speaker 1: the universe.

962
00:46:52,480 --> 00:46:54,759
Speaker 2: Well, I hope that one day we meet aliens from

963
00:46:54,760 --> 00:46:55,960
Speaker 2: a rogue planet.

964
00:46:57,160 --> 00:46:58,160
Speaker 1: And that they're not rogues.

965
00:46:58,200 --> 00:47:01,399
Speaker 2: They're very friendly, that's right, that's right. But Daniel will

966
00:47:01,400 --> 00:47:03,520
Speaker 2: meet them anyway, even if they're going to eat him,

967
00:47:03,560 --> 00:47:05,760
Speaker 2: as long as he gets to ask them about physics verse.

968
00:47:06,480 --> 00:47:08,680
Speaker 1: That's right. Maybe they'll be part of the extraordinaries.

969
00:47:08,960 --> 00:47:10,480
Speaker 2: I hope. So how could they not be?

970
00:47:12,120 --> 00:47:13,680
Speaker 1: All right? So thank you very much for going on

971
00:47:13,680 --> 00:47:16,719
Speaker 1: this trip with us out into intergalactic space and into

972
00:47:16,840 --> 00:47:20,120
Speaker 1: interstellar space to imagine where stars and planets could form.

973
00:47:20,160 --> 00:47:22,520
Speaker 1: If you have questions about the universe, please don't be

974
00:47:22,520 --> 00:47:25,560
Speaker 1: shy right to us. We love tackling your questions on

975
00:47:25,600 --> 00:47:25,959
Speaker 1: the pod.

976
00:47:26,200 --> 00:47:28,600
Speaker 2: And thanks to Steve for his question. Let's go to

977
00:47:28,640 --> 00:47:30,759
Speaker 2: Steve and see what he thought of the episode.

978
00:47:31,320 --> 00:47:35,279
Speaker 3: Yikes, one in five planets are stars are rogue? That

979
00:47:35,440 --> 00:47:38,239
Speaker 3: is way higher odds than I would have given them.

980
00:47:38,440 --> 00:47:41,200
Speaker 3: What I thought was a random idea is estimated to

981
00:47:41,239 --> 00:47:44,480
Speaker 3: be quite common. Who would have thunk it? As you

982
00:47:44,480 --> 00:47:47,680
Speaker 3: have pointed out, this is yet another example of our

983
00:47:47,760 --> 00:47:51,080
Speaker 3: human bias when thinking about the universe. Thank you for

984
00:47:51,160 --> 00:47:54,279
Speaker 3: the answer to my question. Now, with this new knowledge,

985
00:47:54,480 --> 00:47:58,040
Speaker 3: I'm hoping to see a hypervelocity star whiz by Earth

986
00:47:58,280 --> 00:47:59,960
Speaker 3: sometime sooner.

987
00:48:07,120 --> 00:48:10,960
Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We

988
00:48:11,000 --> 00:48:12,399
Speaker 2: would love to hear from you.

989
00:48:12,520 --> 00:48:15,440
Speaker 1: We really would. We want to know what questions you

990
00:48:15,640 --> 00:48:18,280
Speaker 1: have about this Extraordinary Universe.

991
00:48:18,400 --> 00:48:21,319
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992
00:48:21,360 --> 00:48:24,359
Speaker 2: for future shows. If you contact us, we will get

993
00:48:24,400 --> 00:48:24,799
Speaker 2: back to you.

994
00:48:25,040 --> 00:48:28,560
Speaker 1: We really mean it. We answer every message. Email us

995
00:48:28,640 --> 00:48:31,840
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996
00:48:30,880 --> 00:48:32,960
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997
00:48:33,080 --> 00:48:36,880
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998
00:48:36,960 --> 00:48:38,920
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999
00:48:39,360 --> 00:48:40,880
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1000
00:48:41,080 --> 00:48:42,640
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