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Speaker 1: Hey, Daniel, remember a few weeks ago when you insulted

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Speaker 1: America's favorite chocolate bar hershees.

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Speaker 2: How could I forget? I got some strong emails about

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Speaker 2: that comment.

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Speaker 1: Oh yeah, did you get us barred from the airwaves?

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Speaker 2: No? But I think I might have to raise the

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Speaker 2: bar in terms of my comments.

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Speaker 1: You mean we're not already at the bottom.

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Speaker 2: We're scraping the bottom of the bar roll.

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Speaker 1: Yeah, it sounds like you need to spend less time

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Speaker 1: in bars drinking away your chocolate sorrows.

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Speaker 2: I'll have a chocolate TEENI please.

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Speaker 1: Sure give it a shot. Hi am Hori, my cartoonist

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Speaker 1: and the author of Oliver's Great Big Universe. Hi.

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Speaker 2: I'm Daniel. I'm a particle physicist and a professor at

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Speaker 2: U SEE Irvine, and I do have strong opinions about chocolate.

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Speaker 1: Do you have opinions about strong chocolate? Or do you

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Speaker 1: have strong opinions about chocolate?

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Speaker 2: Yes? And yes, it's.

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Speaker 1: Because you're really passionate about chocolate. It gives you a

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Speaker 1: lot of comfort.

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Speaker 2: I feel like, if you're gonna eat chocolate, then you

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Speaker 2: should eat chocolate that you like. But you know, people

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Speaker 2: prefer lots of different kinds of chocolate. I don't mean

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Speaker 2: to judge people who like Hershey's. You know, all the

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Speaker 2: power to them if that's what they want. It's everywhere.

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Speaker 1: I feel like you're maybe being a bit of a

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Speaker 1: chocolate snob.

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Speaker 2: I mean, are you being a snob to know what

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Speaker 2: you like and know what you don't like. I don't

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Speaker 2: want to insult anybody else's preferences to anybody who is

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Speaker 2: offended by me calling Hershey's chocolate garbage, I do apologize.

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Speaker 1: That sounds like a non apology, Daniel.

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Speaker 2: It did sound like an apology. I agree, But it

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Speaker 2: sounded like I was trying, didn't it.

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Speaker 1: I don't think that counts these days. I think you

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Speaker 1: could raise your bar in terms of apologies to the masses.

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Speaker 2: Well, I'll say this, I enjoy chocolate. I hope everybody

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Speaker 2: else out there enjoys chocolate, whatever flavor or variety they prefer. Yeah,

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Speaker 2: there you go.

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Speaker 1: But anyways, welcome to our podcast Daniel and Jorge Explain

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Speaker 1: the Universe, a production of iHeartRadio.

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Speaker 2: In which we whip up a delicious concoction of everything

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Speaker 2: that's out there in the universe, all the dark energy,

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Speaker 2: all the dark matter, all the dark ideas that describe

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Speaker 2: how the universe actually works, what it's made out of,

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Speaker 2: and how it came to be. We melt it all down,

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Speaker 2: form it into squares, and ship it to you over

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Speaker 2: the airwaves.

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Speaker 1: That's right. We try to lower the bar of science

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Speaker 1: and make it accessible to everyone out there. We try

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Speaker 1: to make it silky and smooth and delicious and easy

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Speaker 1: to go down.

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Speaker 2: Because wondering about how the universe works is something everybody does,

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Speaker 2: and everybody should have access to what we know and

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Speaker 2: what we don't know about the universe. Thinking like a

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Speaker 2: physicist is not something only professional physicists can do. It's

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Speaker 2: something everybody can do and should do about how the

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Speaker 2: world works. And we're here to walk you through that.

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Speaker 1: It's right because we all live in the universe. We're

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Speaker 1: all members of the universe, and we can all wonder

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Speaker 1: about how it all works, how it's all put together,

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Speaker 1: and why things are the way they are.

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Speaker 2: Do you have like a membership card for the universe?

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Speaker 2: I don't have one.

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Speaker 1: Oh oh uh, awkward?

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Speaker 2: Awkward.

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Speaker 1: Maybe you just got lost in the mail, Daniel. I'm

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Speaker 1: sure that's what happened. Sure you are invited.

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Speaker 2: Maybe it's part of the Hershey's Cabal. That's secretly organizing

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Speaker 2: the whole universe.

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Speaker 1: Oh you've been you've been blacklisted or dark chocolate listed.

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Speaker 2: Yeah, milk chocolated.

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Speaker 1: That's what you get for insulting hours that be accessible

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Speaker 1: chocolate to the masses. Yeah, but you can still come

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Speaker 1: to the universe.

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Speaker 2: I guess, all right, thank you, you give.

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Speaker 1: Be somebody's plus one. Just don't invite physicist, maybe because

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Speaker 1: there they'll prefer to be on the outside of the

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Speaker 1: universe looking in.

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Speaker 2: No. I love being the part of the universe that's

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Speaker 2: looking at itself, right. That's what makes the questions so important.

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Speaker 2: That we're not outside the universe studying it like some

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Speaker 2: weird objects. It's part of our context, our lives. It's

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Speaker 2: our existence that we're trying to understand. Physics is sometimes

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Speaker 2: sold is like bigger than human But to me, it's

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Speaker 2: the fundamental question of humanity, answering the deepest questions about

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Speaker 2: our own existence.

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Speaker 1: Is it sold as bigger as humanities? Where is that listed?

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Speaker 2: That's how it was sold to me. I guess, so

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Speaker 2: maybe I shouldn't generalize from any equals one. But one

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Speaker 2: reason I got into physics originally was that it seemed

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Speaker 2: like the questions were universal, They weren't limited to things

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Speaker 2: happening on Earth. You know, you study biology, and you

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Speaker 2: know it's fascinating and important, but it might be very

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Speaker 2: different on other planets.

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Speaker 1: Maybe that's why you're not invited, Daniel. You think you're

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Speaker 1: bigger than the rest of us.

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Speaker 2: I think some of the pelophysics is that it does

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Speaker 2: seem to be universal, though of course we don't know,

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Speaker 2: and that's a question we can only answer in the

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Speaker 2: future when we meet aliens.

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Speaker 1: I guess it does sort of tap into that sense

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Speaker 1: of the cosmos, the grand pictures that we all kind

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Speaker 1: of have inside of us. And it is pretty amazing

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Speaker 1: what we've been able to understand and study and come

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Speaker 1: to terms with in terms of where we are in

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Speaker 1: the universe, within our Solar System, within our galaxy, within

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Speaker 1: our supercluster of galaxies, within the observable universe. It's pretty

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Speaker 1: amazing that we can see so much structure out there

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Speaker 1: just by looking out to the night sky.

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Speaker 2: Yeah, it's amazing what we know about the universe, never

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Speaker 2: having left our tiny little neighborhood. Everything we know about

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Speaker 2: the structure of galaxies and superclusters and all that stuff

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Speaker 2: is based just on the few photons that happen to

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Speaker 2: hit Earth from those distant locations. It would be incredible

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Speaker 2: to get in a warp ship and like actually visit

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Speaker 2: some of these places and learn more about what's actually

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Speaker 2: going on there right now. But we can do a

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Speaker 2: pretty impressive job even from here. But of course, there

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Speaker 2: are still lots of unanswered questions about how solar systems form,

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Speaker 2: what planets there are in our Solar system, what planets

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Speaker 2: there have been in our Solar system, and larger questions

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Speaker 2: about galaxies, why they exist, how they form, and why

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Speaker 2: they take their weird shapes.

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Speaker 1: That's right, because we're orbiting around our Sun, and the

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Speaker 1: Sun is orbiting in a galaxy, which is a huge

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Speaker 1: cluster of stars. There are one hundred billion stars in

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Speaker 1: the Milky Way galaxy. But how these galaxies get form

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Speaker 1: is kind of a still up in the air, right.

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Speaker 2: It is, And it's an important question because galaxies are

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Speaker 2: kind of the basic building block of the universe. They're

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Speaker 2: like the atoms of the universe from which you can

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Speaker 2: put together structures and superstructures and all sorts of other stuff.

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Speaker 2: It's incredible that like galaxies actually exist and they tend

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Speaker 2: to be a certain size so it's an important thing

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Speaker 2: to understand, like why are universe features galaxies? How they

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Speaker 2: come to be, how long they will continue to be

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Speaker 2: the basic building block of the universe?

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Speaker 1: Yeah, and why do they have some strange features? And

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Speaker 1: so today on the podcast we'll be asking the question

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Speaker 1: why do some galaxies have bars? Are these like drinking bars?

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Speaker 1: Like our galaxy has a bar, can go and get

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Speaker 1: a drink.

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Speaker 2: There's definitely bars in our galaxy, right, I've been to

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Speaker 2: some of them. So that's a question we can definitively

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Speaker 2: answer today on the podcast.

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Speaker 1: They seem to be closer around Earth at least all

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Speaker 1: the bars we know are on Earth. Is that kind

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Speaker 1: of a physics question or is a biology question?

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Speaker 2: Well? I think there's some history of drinking alcohol in space, right.

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Speaker 2: I think Zach and Kelly's new book has some stories

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Speaker 2: about astronauts who have smuggled things up to the ISS,

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Speaker 2: So perhaps there is an unofficial bar off Earth as well.

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Speaker 1: I wonder if anyone has tried a like brew beer

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Speaker 1: on the space station.

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Speaker 2: Space moonshine, either purpose or by accident. The Moon does

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Speaker 2: shine more brightly in space, so maybe it's easier to

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Speaker 2: make moonshine m there you go. Yeah, And so of

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Speaker 2: course we don't know if aliens enjoy relaxing in bars

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Speaker 2: or whether they like Hershey's chocolate in their chocolate tenies.

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Speaker 2: But today we're not talking about places to drink. We're

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Speaker 2: talking about the structures at the centers of galaxies.

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Speaker 1: I see. So when you say a galaxy bar, it's

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Speaker 1: not like a like a buffet bar or a beer bar.

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Speaker 1: It's more like a destructor. Is a structure in a

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Speaker 1: galaxy that looks like a bar or a structures multiple ones.

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Speaker 2: Yeah, there's a kind of galaxy out there called a

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Speaker 2: barred galaxy, but not every galaxy has this kind of

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Speaker 2: bar at the center, and so it's an open question

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Speaker 2: about why some galaxies have bars.

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Speaker 1: Well, as usually, we were wondering how many people out

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Speaker 1: there had thought about galaxy bars and why some galaxies

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Speaker 1: have them, why some don't? Are they over twenty one?

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Speaker 1: Can you get your favorite drinks in them? And so

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Speaker 1: Daniel went out there into the internet to find out

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Speaker 1: what people think about this question.

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Speaker 2: And whether you like salad bars or chocolate bars or

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Speaker 2: any other kind of bar, You are welcome to participate

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Speaker 2: in this segment of the podcast. Just write to meet

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Speaker 2: you questions at Danielandjorge dot com and I'll set you up.

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Speaker 1: So think about it for a second. Why do you

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Speaker 1: think some galaxies have bars? Here's what peop glad to say.

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Speaker 3: So I didn't know galaxies had bars in the center.

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Speaker 3: So I'm going to say maybe it has it because

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Speaker 3: gravity is aliding them in a special way, but can't

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Speaker 3: be made into sphere because of the black holes gravity.

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Speaker 4: I think planets don't share orbits because the center of

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Speaker 4: gravity would have to be absolutely stationary or it would

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Speaker 4: oscillate and shake itself out of sync. I think that

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Speaker 4: the bars in the center of galaxies are there to

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Speaker 4: give people somewhere to go. But like if women's clothes

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Speaker 4: shops have bars, they have somewhere for men to go

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Speaker 4: instead of trying to look interested.

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Speaker 3: I expect that galaxies have bars at their centers because

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Speaker 3: you're going to need a place to kill some time

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Speaker 3: and have have a beer if your interstellar flight is delayed.

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Speaker 3: I have no idea what does a bar in the

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Speaker 3: center of abilitum?

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Speaker 1: All right, some fun ideas here, some of them a

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Speaker 1: little bit inappropriate.

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Speaker 2: Perhaps I think this might be the highest fraction of

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Speaker 2: joke answers we've ever gotten, which means people really just

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Speaker 2: don't know anything about bars and galaxies.

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Speaker 1: Maybe they're just a barring and not knowing anything about them.

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Speaker 2: Or maybe they'd already spent too much time at a

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Speaker 2: bar when they got these questions and they were in

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Speaker 2: silly mood.

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Speaker 1: Oh there you go. Yeah, maybe you shouldn't send these

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Speaker 1: questions up during happy.

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Speaker 2: Hours Monday morning nine am. Is that what happy hour is?

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Speaker 1: Yeah? Depends on how much you led your job, I guess.

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Speaker 2: And where you are in the world. Right, we have

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Speaker 2: listeners all over the world.

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Speaker 1: Yeah, we are a global podcast. All right, Well, Daniel,

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Speaker 1: maybe step us through this. What exactly do you mean

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Speaker 1: by a galaxy bar?

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Speaker 2: So, galaxy bars are features of one particular kind of galaxy,

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Speaker 2: and galaxies, it turns out, can have all sorts of

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Speaker 2: different shapes in them. Galaxies, of course, are clusters of

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Speaker 2: stars and they can be very very small, from dwarf

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Speaker 2: galaxies that have thousands of stars to super mega galaxies

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Speaker 2: that have billions and billions of stars. But we tend

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Speaker 2: to notice some features in them. And you know, the

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Speaker 2: beginning of any science is basically just bought it, just

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Speaker 2: like look at it. Categorize it, sort it, see what

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Speaker 2: patterns emerge. And very early on when people were studying galaxies,

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Speaker 2: they noticed that they could have different structures, even things

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Speaker 2: we could see here from Earth with limited telescopes.

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Speaker 1: Right, And we've talked a little bit about before the

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Speaker 1: different shapes that galaxies can have, right, And they can

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Speaker 1: be sort of like a blob like a football, or

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Speaker 1: maybe like a spiral, or maybe just like a pancake.

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Speaker 2: Right, yeah, exactly. And there are regular galaxies that are

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Speaker 2: probably in the process of merging between two galaxies. There

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Speaker 2: is a galaxy out there that looks like a question mark,

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Speaker 2: for example. But the most common galaxy out there is

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Speaker 2: a spiral galaxy.

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Speaker 1: How common is it and is it like fifty?

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Speaker 2: It's somewhere around two thirds of all the galaxies that

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Speaker 2: we have studied, our spiral galaxies. And there's a reason

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Speaker 2: for that. And we went into all of that in

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Speaker 2: our recent podcast about the various shapes that galaxies can have.

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Speaker 2: But basically, galaxies form from huge blobs of gas which

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Speaker 2: spin and collapse and then form a disc. And that

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Speaker 2: dense disc gas tends to form those stars, and the

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Speaker 2: spinning of the galaxy turns that disc into a spiral.

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Speaker 1: That's kind of like the default shape of a galaxy, right,

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Speaker 1: But then you can get other shapes, as we talked about,

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Speaker 1: when they merge with each other, other galaxies or they

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Speaker 1: crash into other galaxies.

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Speaker 2: Right exactly. So a spiral galaxy is like the basic

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Speaker 2: building block of the universe in that sense, it's the

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Speaker 2: most important one to understand because the other ones, ellipticals

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Speaker 2: and irregulars are all made out of spiral galaxies. And

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Speaker 2: also our galaxy is a spiral galaxy. So if we're

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Speaker 2: going to understand like the context of our lives, let's

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Speaker 2: begin at.

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Speaker 1: Home, right, And I guess maybe just to paint the

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Speaker 1: picture for folks, by a spiral, it sort of looks

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Speaker 1: like a like a toilet flushing, right, Like, It's not

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Speaker 1: like one like they're tracing out a spiral with a

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Speaker 1: pen and a paper. It's more like a swirl that's

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Speaker 1: kind of converging in the middle.

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Speaker 2: Yeah, And the spiral galaxy usually has several arms. They

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Speaker 2: can have two, sometimes they have three. There are galaxies

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Speaker 2: out there with four arms. Each one is like a

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Speaker 2: spiral that usually goes like one time around. The galaxy

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Speaker 2: starts from the center and then comes out, So it's

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Speaker 2: sort of more like a pinwheel.

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Speaker 1: Right, So that gives you the image of the spiral galaxy.

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Speaker 1: And so that's the basic shape of most galaxies out there.

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Speaker 1: But you say, you're saying some of them have a

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Speaker 1: bar through them or on them.

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Speaker 2: At the center. Some galaxies don't have bars. The spiral

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Speaker 2: arms just start at the very center. But a good

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Speaker 2: fraction galaxy is the center of them. Isn't part of

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Speaker 2: the spiral arm. It's a separate thing. It's like a bar.

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Speaker 2: Like the Milky Way galaxy has this big blob of

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Speaker 2: stars and gas and dust at the center of it,

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Speaker 2: which forms this big bar and the spiral arm that

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Speaker 2: comes out of each end of the bar. So the

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Speaker 2: spirals don't go to the very center of the galaxy.

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Speaker 2: They start at the edges of this bar.

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Speaker 1: WHOA, wait, wait, wait too, you're saying our Milky Way

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Speaker 1: galaxy is a bar.

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Speaker 2: Yes, we live in a bar galaxy.

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Speaker 1: Whoa is it a milk chocolate bar? Since we're the

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Speaker 1: Milky Way.

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Speaker 2: Now I'm afraid to answer because I don't want to

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Speaker 2: anger the Hershey universe cabal that's in charge of everything.

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Speaker 1: Yeah, what if the Milky Way is a hercheese product.

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Speaker 2: This is why it's so important for science to be

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Speaker 2: free of this kind of oppression. People should feel free

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Speaker 2: to speak their minds on chocolate, right.

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Speaker 1: Well, people shouldn't disparage other people if theyread chocolate. I

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Speaker 1: think that is maybe the most important part of your yeah,

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Speaker 1: se point take. But our Milky Way is a bar?

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Speaker 1: Are you saying so? Like our spirals, the arms of

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Speaker 1: our galaxy don't spiral into a single blob in the middle.

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Speaker 1: It's they spiral into a bar.

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Speaker 2: That's right. Our galaxy is two major arms, and then

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Speaker 2: there's some spurs that come off of them, and each

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Speaker 2: arm comes from a different side of the bar. So

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Speaker 2: the two major spirals that make the Milky Way galaxy,

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Speaker 2: they don't actually meet at the center. They come to

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Speaker 2: different sides of this bar that's at the core of

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Speaker 2: the galaxy.

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Speaker 1: Interesting, the picture I'm getting is sort of like I

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Speaker 1: don't know if you've seen those like Hawaiian fire dancers

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Speaker 1: where they have a stick and at each end of

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Speaker 1: the stick it's on fire and so then they spin it.

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Speaker 1: That's kind of sort of what's the picture that we

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Speaker 1: get of the Milky Way galaxy? Isn't it like there's

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Speaker 1: a bar and from the each end of the bar

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Speaker 1: you get these swirls that spiral out.

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Speaker 2: Well, I am not fancy enough to take vacations to Hawaii.

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Speaker 2: Tend to spend my money on chocolate instead. But it

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Speaker 2: sounds accurate.

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Speaker 1: You know that you can get chocolate in Hawaii. In fact,

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Speaker 1: it's kind of known for they're kind of known for

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Speaker 1: having good chocolate.

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Speaker 2: Macademian that chocolate here, I come, there you go. But yeah,

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Speaker 2: that sounds accurate. Wow. Or if you imagine like a

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Speaker 2: baton twirler at a football game and ribbons at the

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Speaker 2: end of the baton. If he or she spins the baton,

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Speaker 2: then the ribbons spiral around it. But the ribbons, of course,

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Speaker 2: don't meet at the very center. They come from the

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Speaker 2: edges of the bed.

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Speaker 1: Now, this is an interesting idea just because to me

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Speaker 1: and I wonder if to a lot of our listeners

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Speaker 1: this is kind of news. Right, Like most of the

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Speaker 1: time that you see a picture or a drawing of

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Speaker 1: the milk Away Galaxy, they don't it doesn't have the

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Speaker 1: bar in the middle, right like the famous isn't the

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Speaker 1: famous image of like you are here? Or it points

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Speaker 1: to a point in the Milk Away. Of a drawing

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Speaker 1: of the milk Away that one doesn't have a bar,

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Speaker 1: I don't think.

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Speaker 2: Yeah, that's a good point. I'm not sure if that

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Speaker 2: image is scientifically vetted. It also really doesn't have big

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Speaker 2: distinct arms the way you might expect, But a more

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Speaker 2: scientifically accurate picture of the Milky Way shows the specific

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Speaker 2: arms and the bar. The bar is not like a

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Speaker 2: very rigid rod. It's a bit of a blob also to.

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Speaker 1: Me now of stars, like a just an elongated cluster

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Speaker 1: of stars.

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Speaker 2: Yeah, it's stars, and it's gas and it's dust like

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Speaker 2: the rest of the galaxy. But you know, this is

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Speaker 2: us imposing order on a huge swirling mass of stuff.

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Speaker 2: So part of this, of course, is just the impression

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Speaker 2: we make, how our brains filter the full details of

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Speaker 2: the buzzing chaos of reality.

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Speaker 1: All right, Well, so then the Milkway has a bar.

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Speaker 1: Lots of galaxies maybe have bars in the middle of them,

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Speaker 1: and so the question is why do they have bars,

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Speaker 1: What's going on there in the middle of the galaxy?

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Speaker 1: And can you play galactic limbo with that bar? And

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Speaker 1: so let's get to these deep and profound questions. But

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Speaker 1: first let's take a quick all right, we're talking about

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Speaker 1: the Milky Way galaxy and the fact that it has

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Speaker 1: a bar of stars in the middle. The swirls of

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Speaker 1: the galaxy don't converge to a round blob in the middle.

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Speaker 1: They converse to kind of like a rod of stars. Right.

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Speaker 2: Yeah, it might be more accurate to call it like

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Speaker 2: a football because it's a little wider in the center

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Speaker 2: than it is at the edges. But yeah, there's sort

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Speaker 2: of a long.

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Speaker 1: But it's not a bar. Why don't we just call

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Speaker 1: them football galaxy?

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Speaker 2: Football galaxy? That sounds great. I am done defending the

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Speaker 2: naming schemes of astronomy.

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Speaker 1: Because it's indefensible, because you just can't do it.

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Speaker 2: Sorry, astronomers, you have no champion in me anymore.

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Speaker 1: Oh boy, you're throwing the astronomers under the bus.

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Speaker 2: No, I'm just throwing.

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Speaker 1: Naming peculiarities.

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Speaker 2: Oh, it certainly does. And nobody's ever asked me my

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Speaker 2: opinion when they make up these names.

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Speaker 1: Okay, So the Milky Way has a bar or football

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Speaker 1: kind of in the middle, which is weird, right, because

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Speaker 1: you would expect a galaxy to be sort of, you know,

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Speaker 1: round and symmetric, right.

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Speaker 2: You would kind of expect it. And that's exactly why

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Speaker 2: we are really interested in these questions like what structures

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Speaker 2: form in the universe. The answer to that question reveals

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Speaker 2: the forces at play. Like wire galaxies created in the

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Speaker 2: first place, Well, there's gravity, why don't they just collapse

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Speaker 2: into a central ball, while there's angular momentum that turns

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Speaker 2: them into disks? Why do the arms form at all?

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Speaker 1: Well, maybe a question we can ask here is like

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Speaker 1: what percentage of galaxies are barred galaxies? Like, is the

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Speaker 1: Milky Way super weird that it has a bar? Or

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Speaker 1: is it like most spiral galaxies have bars or some

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Speaker 1: of them or fifty to fifty.

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Speaker 2: That's a really interesting question, and the answer depends on

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Speaker 2: the mass of the galaxy in a super weird way

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Speaker 2: for galaxies about the mass of the Milky Way, like

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Speaker 2: billions and billions of solar masses. It's around two thirds

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Speaker 2: of spiral galaxies that have bars. The more massive the galaxy,

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Speaker 2: the smaller the fraction of the spirals have bars. And

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Speaker 2: also the less massive the galaxy, the smaller fraction have bars.

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Speaker 2: So there is this like sweet spot in the middle

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Speaker 2: where galaxies are more likely to have bars. And if

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Speaker 2: you move away from that lower mass or higher mass,

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Speaker 2: then the fraction that have bars decreases.

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Speaker 1: M interesting, So it depends on the size and mass

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Speaker 1: of the galaxy. But maybe let's take a back to

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Speaker 1: the basics, because it sounds like there's a lot of

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Speaker 1: physics lying on here, as you might expect from our podcasts,

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Speaker 1: But so what's going on at the center? Like how

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Speaker 1: can this bar still be there after all these billions

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Speaker 1: of years?

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Speaker 2: It all comes from asymmetries like little over densities. If

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Speaker 2: you start from a galaxy that was perfectly smooth, like

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Speaker 2: all the matter was evenly distributed, or like you had

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Speaker 2: a cluster of stars that were perfectly distributed in circles

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Speaker 2: on perfectly circular orbits, then it wouldn't form a bar.

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Speaker 2: You tweak it a little bit, like one little spot

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Speaker 2: has more density than another spot, then that spot's going

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Speaker 2: to have more gravity and it's going to attract more

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Speaker 2: stars to it, and so you get these density waves

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Speaker 2: forming inside the galaxy. So the same process that forms

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Speaker 2: the arms, theives density waves of the arms that we

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Speaker 2: describe as like traffic passing through a freeway, can also

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Speaker 2: form density structures in the center of the galaxy and

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Speaker 2: in this case, they form bars.

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Speaker 1: Well, yeah, I remember we spent a whole episode talking

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Speaker 1: about this idea of density waves in a galaxy. It's

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Speaker 1: not like the arm of a galaxy what you see

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Speaker 1: as a soirl like, it doesn't rotate around the galaxy.

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Speaker 1: It's more like a ripple through a whole bunch of stars.

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Speaker 2: Exactly. It's more like a ripple. It's like people doing

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Speaker 2: the wave in a football stadium. They're not moving sidewaves,

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Speaker 2: but the wave itself is moving, right, And so the

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Speaker 2: galaxy arms are waves in the density of stars, and

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Speaker 2: the bar is the same way. The bar is like

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Speaker 2: a density wave. So it's a structure that forms, but

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Speaker 2: it moves through the stars. It doesn't move at the

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Speaker 2: same speed the stars are moving around the galaxy. It

441
00:21:06,000 --> 00:21:07,760
Speaker 2: can move faster, it can move slower.

442
00:21:08,160 --> 00:21:09,760
Speaker 1: Wait, what do you mean the bar? Does a bar

443
00:21:09,920 --> 00:21:13,720
Speaker 1: rotate and bar devastates moving like, which direction is the

444
00:21:13,760 --> 00:21:14,240
Speaker 1: bar moving?

445
00:21:14,480 --> 00:21:17,600
Speaker 2: The bar rotates the same direction as the galaxy and

446
00:21:17,640 --> 00:21:18,680
Speaker 2: it definitely rotates.

447
00:21:18,840 --> 00:21:20,720
Speaker 1: Oh, kind of like the arms and a clock.

448
00:21:21,119 --> 00:21:22,960
Speaker 2: Kind of like the arms and a clock, and also

449
00:21:23,119 --> 00:21:26,200
Speaker 2: like the arms of the galaxy. Right, because the arms

450
00:21:26,240 --> 00:21:30,679
Speaker 2: are density waves, they move relative to the stars, So

451
00:21:30,760 --> 00:21:32,600
Speaker 2: one star might be in the density wave and then

452
00:21:32,640 --> 00:21:35,159
Speaker 2: they'll get passed by the density wave which moves on.

453
00:21:35,640 --> 00:21:38,960
Speaker 1: WHOA are there like videos online about this? That would

454
00:21:39,000 --> 00:21:39,840
Speaker 1: be cool to see.

455
00:21:39,680 --> 00:21:42,080
Speaker 2: You mean, like actual footage of bars rotating, not.

456
00:21:42,280 --> 00:21:43,639
Speaker 1: Like a simulation or something.

457
00:21:43,720 --> 00:21:45,440
Speaker 2: Yeah, I would love to see that, but the time

458
00:21:45,480 --> 00:21:47,960
Speaker 2: scales are ridiculous, Like the Milky Way takes two hundred

459
00:21:47,960 --> 00:21:51,600
Speaker 2: and fifty million years to rotate, So there's no chance

460
00:21:51,640 --> 00:21:54,800
Speaker 2: for like, watch a galaxy rotate unless you're gonna set

461
00:21:54,840 --> 00:21:56,560
Speaker 2: it your camera for tens of millions of years.

462
00:21:56,600 --> 00:21:58,120
Speaker 1: So wait, how do we know it's rotating.

463
00:21:58,560 --> 00:22:00,840
Speaker 2: Well, we build up a model of how galaxy works

464
00:22:00,880 --> 00:22:03,639
Speaker 2: that includes angular momentum, and you need those components that

465
00:22:03,760 --> 00:22:07,080
Speaker 2: rotation to explain what we see. If they weren't rotating,

466
00:22:07,200 --> 00:22:09,920
Speaker 2: there's no anglar momentum, and these things would collapse a

467
00:22:09,960 --> 00:22:12,119
Speaker 2: lot faster. A lot of galaxies and a lot of these

468
00:22:12,119 --> 00:22:15,440
Speaker 2: structures are supported by angular momentum. Like, where else would

469
00:22:15,440 --> 00:22:17,840
Speaker 2: the spiral arms come from if it wasn't spinning.

470
00:22:18,320 --> 00:22:18,760
Speaker 1: I don't know.

471
00:22:19,160 --> 00:22:21,440
Speaker 2: Yeah, So we do a lot of simulations to try

472
00:22:21,440 --> 00:22:23,480
Speaker 2: to explain the galaxies we see. We said, well, we

473
00:22:23,480 --> 00:22:25,480
Speaker 2: think we understand all the forces at play. We put

474
00:22:25,480 --> 00:22:27,320
Speaker 2: it in the computer, we press the button, it goes,

475
00:22:27,320 --> 00:22:29,359
Speaker 2: and we see what comes out of the simulation. Then

476
00:22:29,400 --> 00:22:32,200
Speaker 2: we compare that to what we see in the sky. Interesting,

477
00:22:32,320 --> 00:22:34,639
Speaker 2: that's what we do to try to explain what's happening

478
00:22:34,720 --> 00:22:37,000
Speaker 2: or try to gain some understanding of the forces at work.

479
00:22:37,160 --> 00:22:40,800
Speaker 1: Wow, so nobody's ever actually seen a galaxy swirling. We

480
00:22:40,960 --> 00:22:44,840
Speaker 1: just think it does. I mean, it's the most likely

481
00:22:44,960 --> 00:22:47,960
Speaker 1: or obvious explanation, but still it's a fact that we

482
00:22:48,040 --> 00:22:51,440
Speaker 1: haven't seen a galaxy swirl. Like, we've only seen a

483
00:22:51,480 --> 00:22:53,840
Speaker 1: photograph of it. It's like you've only seen a photograph

484
00:22:54,280 --> 00:22:57,159
Speaker 1: where Merry go round. Ever, like you've never seen a

485
00:22:57,160 --> 00:22:58,280
Speaker 1: mirror go around move.

486
00:23:00,000 --> 00:23:02,480
Speaker 2: Well, that's true when we've only even known about other

487
00:23:02,560 --> 00:23:05,760
Speaker 2: galaxies for like one hundred years. It was Hubble who

488
00:23:05,760 --> 00:23:08,920
Speaker 2: saw these little smudges in the sky and deduced their

489
00:23:09,000 --> 00:23:13,920
Speaker 2: distance from analyzing special stars in them, the sephids, whose brightness,

490
00:23:13,920 --> 00:23:17,439
Speaker 2: of course is famously connected to their pulsing frequency. And

491
00:23:17,480 --> 00:23:19,680
Speaker 2: he's the one that understood that these things were outside

492
00:23:19,800 --> 00:23:23,280
Speaker 2: our galaxy. So we only known that other galaxies exist

493
00:23:23,400 --> 00:23:26,119
Speaker 2: for like one hundred years and had good enough telescopes

494
00:23:26,160 --> 00:23:29,560
Speaker 2: to like resolve their structure for a few decades, which

495
00:23:29,600 --> 00:23:32,680
Speaker 2: is basically no time at all relative to their actual emotion.

496
00:23:33,160 --> 00:23:36,240
Speaker 2: So yeah, we're studying galaxies basically frozen in time.

497
00:23:36,720 --> 00:23:40,439
Speaker 1: Well that's interesting. Now you're saying that about two thirds

498
00:23:40,440 --> 00:23:43,160
Speaker 1: of galaxies have a bar in the middle of them,

499
00:23:43,400 --> 00:23:46,560
Speaker 1: and this bar is rotating and rippling through the center

500
00:23:47,119 --> 00:23:50,040
Speaker 1: of the galaxy. Like what's the mechanism for making these bars?

501
00:23:50,160 --> 00:23:52,240
Speaker 1: Like why not? Why a bar shape? Why not a

502
00:23:52,320 --> 00:23:55,240
Speaker 1: star shape or a banana shape.

503
00:23:56,359 --> 00:23:58,159
Speaker 2: I would love to see a banana shape at the

504
00:23:58,200 --> 00:24:01,240
Speaker 2: center of galaxy and probably some galaxy out there that

505
00:24:01,320 --> 00:24:03,960
Speaker 2: has that, because there's so many galaxies out there and

506
00:24:04,000 --> 00:24:05,840
Speaker 2: so many of them are doing weird things.

507
00:24:06,000 --> 00:24:08,760
Speaker 1: I guess if you think about a galaxy, is banana shape,

508
00:24:08,800 --> 00:24:10,760
Speaker 1: Like each arm is like a banana. So it's like

509
00:24:10,800 --> 00:24:13,680
Speaker 1: if you take if you take several bananas and arrange

510
00:24:13,720 --> 00:24:16,840
Speaker 1: them in a star shape, you would get a spiral galaxy.

511
00:24:16,920 --> 00:24:19,120
Speaker 2: Right, Yeah, that's true. That's a message from the universe

512
00:24:19,480 --> 00:24:21,040
Speaker 2: that bananas are important, and you.

513
00:24:21,000 --> 00:24:23,800
Speaker 1: Start with them in chocolate this they're galactic.

514
00:24:25,160 --> 00:24:28,000
Speaker 2: And that's why we sell frozen chocolate covered bananas here

515
00:24:28,040 --> 00:24:28,920
Speaker 2: in Orange County.

516
00:24:29,040 --> 00:24:31,800
Speaker 1: That is the purpose of the universe, isn't it? Is

517
00:24:31,800 --> 00:24:39,840
Speaker 1: it deep fried too? Why not fried chocolate covered bananas?

518
00:24:41,040 --> 00:24:43,160
Speaker 1: I think I've had that at a restaurant, actually.

519
00:24:43,040 --> 00:24:45,960
Speaker 2: But you asked a great question that wasn't about dessert,

520
00:24:46,000 --> 00:24:48,800
Speaker 2: which is why do some galaxies have bars? Why do

521
00:24:48,840 --> 00:24:51,560
Speaker 2: they form bar shapes and not other things? And the

522
00:24:51,560 --> 00:24:54,400
Speaker 2: answer is that we're not sure, Like we don't understand

523
00:24:54,440 --> 00:24:57,920
Speaker 2: why some galaxies form bars and some don't. We don't

524
00:24:58,080 --> 00:25:02,240
Speaker 2: totally understand the mechanism for the formation itself. Like we've

525
00:25:02,240 --> 00:25:05,560
Speaker 2: seen this happen in simulation sometimes and it comes out

526
00:25:05,600 --> 00:25:07,960
Speaker 2: of instabilities. You put a bunch of stars a little

527
00:25:07,960 --> 00:25:10,200
Speaker 2: bit closer to each other, they tend to form these

528
00:25:10,240 --> 00:25:13,840
Speaker 2: density waves. And what's happening here at the center is

529
00:25:13,840 --> 00:25:16,680
Speaker 2: that the stars are no longer totally in a circular orbit.

530
00:25:17,040 --> 00:25:19,840
Speaker 2: The bar like twists the orbits so that some stars are

531
00:25:19,840 --> 00:25:23,639
Speaker 2: moving more on radial orbits passing close through the center

532
00:25:23,720 --> 00:25:24,480
Speaker 2: of the galaxy.

533
00:25:24,720 --> 00:25:27,359
Speaker 1: What do you mean, radar like more oval shape orbits?

534
00:25:27,520 --> 00:25:30,080
Speaker 2: Yeah, more oval shape, So they're not equally distributed around

535
00:25:30,080 --> 00:25:32,879
Speaker 2: the center of the galaxy. They're like passing back and forth.

536
00:25:33,200 --> 00:25:36,280
Speaker 1: Oh interesting, I guess maybe it's sort of rare or

537
00:25:36,400 --> 00:25:38,560
Speaker 1: sort of a coincid is that you would have circular

538
00:25:38,720 --> 00:25:40,639
Speaker 1: orbit orbits, right Like, if I throw a rock at

539
00:25:40,640 --> 00:25:42,840
Speaker 1: the Sun right now, it would not necessarily go in

540
00:25:42,880 --> 00:25:45,399
Speaker 1: a round orbit. It might maybe more likely go in

541
00:25:45,440 --> 00:25:46,760
Speaker 1: an oval shape orbit.

542
00:25:46,960 --> 00:25:49,280
Speaker 2: Yeah, there's lots of possible solutions, and a circle is

543
00:25:49,280 --> 00:25:51,800
Speaker 2: like a special case of it. And also to maintain

544
00:25:51,880 --> 00:25:55,399
Speaker 2: a circular orbit requires resisting the tugs and the pulls

545
00:25:55,400 --> 00:25:58,560
Speaker 2: of everything else around you. Remember that you're not orbiting

546
00:25:58,560 --> 00:26:01,159
Speaker 2: by yourself. The Earth is being on by Jupiter, and

547
00:26:01,240 --> 00:26:03,440
Speaker 2: Jupiter is being pulled on by everything else. That's one

548
00:26:03,440 --> 00:26:06,399
Speaker 2: of the reasons why our orbits are eccentric. So the

549
00:26:06,400 --> 00:26:09,800
Speaker 2: more complicated dynamics you have, the more lack of symmetry,

550
00:26:09,960 --> 00:26:12,280
Speaker 2: the more these things are getting pulled by other stuff,

551
00:26:12,400 --> 00:26:14,480
Speaker 2: the more they're going to fall out of perfectly circular

552
00:26:14,560 --> 00:26:18,800
Speaker 2: orbits and clump together in other kinds of orbits.

553
00:26:18,359 --> 00:26:20,600
Speaker 1: So that you're saying, the stuff at the center of

554
00:26:20,640 --> 00:26:23,840
Speaker 1: our milk away galaxy is not necessarily going around in

555
00:26:23,840 --> 00:26:26,400
Speaker 1: a circle, it's maybe going in an oval shape around

556
00:26:26,400 --> 00:26:29,679
Speaker 1: the center. But then how does that explain the ripple

557
00:26:29,840 --> 00:26:32,520
Speaker 1: that is the bar or all of these things going

558
00:26:32,560 --> 00:26:33,800
Speaker 1: in an oval in sync.

559
00:26:34,119 --> 00:26:37,000
Speaker 2: Yes, the bar itself is like a denser region which

560
00:26:37,080 --> 00:26:40,960
Speaker 2: passes through the center of the galaxy, and it influences

561
00:26:41,000 --> 00:26:43,800
Speaker 2: other stuff. So gas near the center of the galaxy,

562
00:26:43,840 --> 00:26:47,320
Speaker 2: for example, moves at faster speeds than gas further out,

563
00:26:47,480 --> 00:26:49,479
Speaker 2: So the gas can catch up to the bar and

564
00:26:49,560 --> 00:26:52,120
Speaker 2: pass through it. But then the bar is stronger gravity

565
00:26:52,200 --> 00:26:55,320
Speaker 2: slows it down, so the material tends to lose some energy.

566
00:26:56,000 --> 00:26:58,800
Speaker 2: This actually ends up funneling a bunch more gas towards

567
00:26:58,840 --> 00:27:01,879
Speaker 2: the center of the galaxy and can create new stars

568
00:27:02,080 --> 00:27:03,040
Speaker 2: right there in the bar.

569
00:27:03,200 --> 00:27:06,280
Speaker 1: But then, I guess, like making the bar is so common,

570
00:27:06,480 --> 00:27:09,280
Speaker 1: you're seeing about two thirds of galaxies, spiral galaxies have

571
00:27:09,320 --> 00:27:11,600
Speaker 1: a bar in them. Why don't we see that effect

572
00:27:11,680 --> 00:27:14,840
Speaker 1: like in other places, like when I flushed the toilet,

573
00:27:15,000 --> 00:27:17,640
Speaker 1: or you know, in our Solar system. Even we don't

574
00:27:17,640 --> 00:27:19,520
Speaker 1: have a bar in our solar system. I guess we

575
00:27:19,560 --> 00:27:23,000
Speaker 1: don't have spiral arms in our Solar system either, Like

576
00:27:23,240 --> 00:27:25,800
Speaker 1: you know, things coalesced into the planets, although we do

577
00:27:25,880 --> 00:27:26,800
Speaker 1: have an asteroid built.

578
00:27:27,560 --> 00:27:29,639
Speaker 2: I think it comes down to the balance of all

579
00:27:29,680 --> 00:27:31,600
Speaker 2: the things at play. You know, we have gravity in

580
00:27:31,640 --> 00:27:33,720
Speaker 2: the Solar System, and of course in the galaxy. But

581
00:27:33,760 --> 00:27:36,040
Speaker 2: the galaxy is a lot more friction. You know, there's

582
00:27:36,160 --> 00:27:38,760
Speaker 2: gas and there's dust. This stuff is interacting much more

583
00:27:38,800 --> 00:27:41,040
Speaker 2: than things in the Solar system. So there's a lot

584
00:27:41,040 --> 00:27:44,120
Speaker 2: more transfer of energy between the stuff in the galaxy

585
00:27:44,160 --> 00:27:46,520
Speaker 2: than there is in the Solar system. Solar systems like

586
00:27:46,520 --> 00:27:48,639
Speaker 2: a cleaned up little galaxy. There's not nearly as much

587
00:27:48,680 --> 00:27:51,200
Speaker 2: stuff between the planets as there is between the stars.

588
00:27:51,240 --> 00:27:54,040
Speaker 2: In the galaxy. There's a lot more of this exchange

589
00:27:54,040 --> 00:27:57,080
Speaker 2: of energy and friction and stuff bumping into other stuff

590
00:27:57,400 --> 00:28:00,439
Speaker 2: in the galaxy, which can give you more interesting complex

591
00:28:00,640 --> 00:28:04,320
Speaker 2: basically turbulent structure. And we don't know how long these

592
00:28:04,359 --> 00:28:07,320
Speaker 2: bars last. There's some theories that say these bars will

593
00:28:07,400 --> 00:28:09,919
Speaker 2: last forever, and we see some galaxies that have had

594
00:28:10,000 --> 00:28:12,920
Speaker 2: their bars for like ten billion years. There are other

595
00:28:12,960 --> 00:28:15,800
Speaker 2: theories that the bars could be oscillatory, like maybe the

596
00:28:15,800 --> 00:28:18,240
Speaker 2: bar forms, but then the formation of the bar tends

597
00:28:18,280 --> 00:28:20,439
Speaker 2: to destroy the bar, and then another bar forms a

598
00:28:20,480 --> 00:28:23,120
Speaker 2: billion years later. So it could be that every galaxy

599
00:28:23,200 --> 00:28:25,359
Speaker 2: goes through phases where it has a bar and doesn't

600
00:28:25,359 --> 00:28:28,000
Speaker 2: have a bar. These are really open questions in the

601
00:28:28,000 --> 00:28:29,240
Speaker 2: study of galaxy formation.

602
00:28:29,600 --> 00:28:33,200
Speaker 1: Mmmm, it's doing like pull ups or something on a bar,

603
00:28:34,359 --> 00:28:37,800
Speaker 1: going back and forth. But this is an interesting idea

604
00:28:37,840 --> 00:28:40,200
Speaker 1: that it maybe depends on time. Like you're saying, they

605
00:28:40,240 --> 00:28:43,160
Speaker 1: can come in and out. What do you see when

606
00:28:43,200 --> 00:28:44,960
Speaker 1: you look at the galaxies out there in the universe, Like,

607
00:28:45,040 --> 00:28:49,920
Speaker 1: don't can't we see them across different ages and times? Yeah?

608
00:28:50,000 --> 00:28:52,960
Speaker 1: Do we see that the older galaxies have more bars

609
00:28:53,040 --> 00:28:55,240
Speaker 1: or younger galaxies have more bars? What do we see?

610
00:28:55,400 --> 00:28:57,320
Speaker 2: Yeah, so we're not sure. We have a lot of

611
00:28:57,360 --> 00:28:59,640
Speaker 2: different clues that sort of point us in different directions. Like,

612
00:28:59,680 --> 00:29:03,160
Speaker 2: on one hand, we see some galaxies with really really

613
00:29:03,200 --> 00:29:06,160
Speaker 2: old bars. I was reading a paper about a galaxy

614
00:29:06,360 --> 00:29:09,080
Speaker 2: we're looking at ten billion years in the past, and

615
00:29:09,120 --> 00:29:11,640
Speaker 2: we can see the formation of a bar back then.

616
00:29:12,040 --> 00:29:14,880
Speaker 2: So that's just like some bars formed really early in

617
00:29:14,960 --> 00:29:17,920
Speaker 2: the universe and may have lasted a really long time.

618
00:29:18,280 --> 00:29:20,760
Speaker 2: Of course, you can't see the same galaxy over time.

619
00:29:21,160 --> 00:29:21,960
Speaker 1: Yeah, how do we know?

620
00:29:22,280 --> 00:29:25,080
Speaker 2: We don't know necessarily how long a bar lasts when

621
00:29:25,120 --> 00:29:27,840
Speaker 2: it's formed. But in this one particular galaxy, they could

622
00:29:27,840 --> 00:29:31,400
Speaker 2: see evidence of the bar over about ten billion years

623
00:29:31,680 --> 00:29:34,400
Speaker 2: because they could see how the bar had disrupted the

624
00:29:34,440 --> 00:29:37,840
Speaker 2: structure of the galaxy. So it's a little speculative, but

625
00:29:38,120 --> 00:29:40,520
Speaker 2: they think that that bar lasted for about ten billion

626
00:29:40,560 --> 00:29:43,520
Speaker 2: years in that galaxy because of how it like shepherded

627
00:29:43,800 --> 00:29:46,920
Speaker 2: the stars and influence the gas to create new stars.

628
00:29:47,240 --> 00:29:49,719
Speaker 2: So it's not everybody that believes that paper, but that

629
00:29:49,760 --> 00:29:52,880
Speaker 2: one paper argues that there are galaxies with really long

630
00:29:53,000 --> 00:29:53,680
Speaker 2: lived bars.

631
00:29:54,960 --> 00:29:56,239
Speaker 1: And then I guess, how do you know that they

632
00:29:56,280 --> 00:29:56,920
Speaker 1: can go away?

633
00:29:57,120 --> 00:30:00,640
Speaker 2: Yeah, another great question. That's again from simulation. We see

634
00:30:00,680 --> 00:30:04,240
Speaker 2: in some simulations that a bar can like drive gas

635
00:30:04,280 --> 00:30:06,840
Speaker 2: inwards towards the center of the galaxy. It's an over

636
00:30:06,880 --> 00:30:09,480
Speaker 2: density and so it pulls stuff in and that can

637
00:30:09,560 --> 00:30:13,160
Speaker 2: disrupt the motion of stars through the galactic core. So,

638
00:30:13,200 --> 00:30:16,080
Speaker 2: like the formation of the bar could create gravity which

639
00:30:16,160 --> 00:30:19,920
Speaker 2: pulls in more gas, which ends up disrupting the bar itself.

640
00:30:20,480 --> 00:30:22,280
Speaker 2: So we don't know. And this is the kind of

641
00:30:22,280 --> 00:30:25,800
Speaker 2: thing we study in simulations, and these simulations are never perfect, right,

642
00:30:25,800 --> 00:30:28,640
Speaker 2: You can't include everything in the galaxy in your simulation,

643
00:30:28,760 --> 00:30:31,960
Speaker 2: every tiny particle. It would take forever. So whenever they

644
00:30:31,960 --> 00:30:35,120
Speaker 2: do these simulations, they're always making approximations. Well, let's leave

645
00:30:35,120 --> 00:30:37,240
Speaker 2: out the dark matter, or let's ignore this effect. Or

646
00:30:37,400 --> 00:30:39,880
Speaker 2: something to make it tractable. And so you've got lots

647
00:30:39,880 --> 00:30:42,640
Speaker 2: of different simulations with sort of different answers, and people

648
00:30:42,680 --> 00:30:45,120
Speaker 2: are still exploring this, like right now, nobody really knows

649
00:30:45,120 --> 00:30:46,360
Speaker 2: the answers to these questions.

650
00:30:46,440 --> 00:30:49,600
Speaker 1: So when you simulate it, you add a little asymmetry

651
00:30:49,720 --> 00:30:52,760
Speaker 1: or like an offset to the distribution of the stars,

652
00:30:52,800 --> 00:30:54,680
Speaker 1: and then you get a bar. And then what you

653
00:30:54,680 --> 00:30:57,120
Speaker 1: see in the simulation is that sometimes the bar disappears

654
00:30:57,120 --> 00:31:00,000
Speaker 1: after a while exactly, and then maybe it comes back

655
00:31:00,120 --> 00:31:01,240
Speaker 1: later mm hmm.

656
00:31:01,680 --> 00:31:04,520
Speaker 2: And there's some other hints from the simulations. Some suggest

657
00:31:04,720 --> 00:31:07,960
Speaker 2: that it depends on the thickness of the disk. Like

658
00:31:07,960 --> 00:31:11,080
Speaker 2: our galaxies mostly flat, but it's not a totally thin disk.

659
00:31:11,480 --> 00:31:14,120
Speaker 2: It's not like it's a paper thin, right, There's a

660
00:31:14,200 --> 00:31:17,320
Speaker 2: width to the galaxy, and some galaxies have thinner disks

661
00:31:17,360 --> 00:31:20,400
Speaker 2: and some galaxies have thicker discs, And some of these

662
00:31:20,400 --> 00:31:24,240
Speaker 2: stimulations suggest that galaxies with thinner discs are more likely

663
00:31:24,320 --> 00:31:27,600
Speaker 2: to have bars than galaxies with thicker discs in them.

664
00:31:27,840 --> 00:31:28,840
Speaker 1: WHOA why would they be?

665
00:31:29,160 --> 00:31:31,720
Speaker 2: I think it has to do with basically the gravitational

666
00:31:31,840 --> 00:31:35,160
Speaker 2: environment in which a disruption forms, Like if there's a

667
00:31:35,200 --> 00:31:38,720
Speaker 2: lot of other gravity happening anyway, then the small over

668
00:31:38,760 --> 00:31:41,640
Speaker 2: density is less likely to cause a big pile up

669
00:31:41,720 --> 00:31:44,120
Speaker 2: in the galactic spin. Like, for example, you had a

670
00:31:44,160 --> 00:31:46,880
Speaker 2: huge amount of dark matter in your galaxy and then

671
00:31:46,880 --> 00:31:49,440
Speaker 2: the gravity of the galaxy is mostly dominated by that

672
00:31:49,560 --> 00:31:51,560
Speaker 2: dark matter. In the same way, if you have lots

673
00:31:51,560 --> 00:31:53,720
Speaker 2: of other stars like above and below where the over

674
00:31:53,760 --> 00:31:56,080
Speaker 2: density forms, then those stars are going to tend to

675
00:31:56,120 --> 00:31:59,400
Speaker 2: smooth stuff out because of their gravity. A thicker disc

676
00:31:59,480 --> 00:32:02,280
Speaker 2: might prevent a little over density from turning into a

677
00:32:02,280 --> 00:32:02,720
Speaker 2: big bar.

678
00:32:03,000 --> 00:32:05,360
Speaker 1: Interesting, it's like a two D effect, like it only

679
00:32:05,400 --> 00:32:06,720
Speaker 1: happens in thin sheets.

680
00:32:06,960 --> 00:32:11,160
Speaker 2: Yeah, it could be. Another study suggested that mergers can

681
00:32:11,200 --> 00:32:14,880
Speaker 2: destroy bars. Remember, spiral galaxies merge and form sometimes new

682
00:32:14,920 --> 00:32:18,960
Speaker 2: spiral galaxies, sometimes elliptical galaxies, And it could be that

683
00:32:19,080 --> 00:32:21,520
Speaker 2: bars are destroyed in these mergers, and then the new

684
00:32:21,560 --> 00:32:24,560
Speaker 2: galaxy doesn't necessarily have a bar. It depends on the

685
00:32:24,560 --> 00:32:28,480
Speaker 2: instability and the formation of the stars in that new galaxy. WHOA,

686
00:32:29,040 --> 00:32:31,200
Speaker 2: but there's another really interesting clue. And to answer a

687
00:32:31,240 --> 00:32:33,840
Speaker 2: question you asked a few minutes ago about whether bars

688
00:32:33,880 --> 00:32:36,800
Speaker 2: form more recently or not, we find that it also

689
00:32:36,920 --> 00:32:39,720
Speaker 2: depends on the mass of the galaxy. So a lot

690
00:32:39,760 --> 00:32:42,280
Speaker 2: of the bars tend to have formed more recently in

691
00:32:42,520 --> 00:32:45,840
Speaker 2: lower mass galaxies. So it might be that lower mass

692
00:32:45,880 --> 00:32:48,960
Speaker 2: galaxies take longer to form stars and then take longer

693
00:32:48,960 --> 00:32:51,600
Speaker 2: to form bars. So most of the bars that are

694
00:32:51,640 --> 00:32:53,880
Speaker 2: forming in the universe today we think are in the

695
00:32:53,960 --> 00:32:57,080
Speaker 2: lower mass galaxies. They might not just have had time

696
00:32:57,160 --> 00:32:58,720
Speaker 2: to make a bar until now.

697
00:32:59,240 --> 00:33:02,840
Speaker 1: So you need like time and mass and flatness to

698
00:33:02,880 --> 00:33:03,520
Speaker 1: make a bar.

699
00:33:03,520 --> 00:33:06,800
Speaker 2: And some sort of seed, right, some gravitational over density.

700
00:33:07,280 --> 00:33:09,760
Speaker 2: I think it's really fascinating that basically all the structure

701
00:33:09,800 --> 00:33:13,280
Speaker 2: in the universe comes from one place being heavier than another.

702
00:33:13,680 --> 00:33:16,280
Speaker 2: When the universe began, if it was totally smooth, nothing

703
00:33:16,280 --> 00:33:18,960
Speaker 2: would have happened because all the gravity would have been balanced.

704
00:33:19,360 --> 00:33:22,760
Speaker 2: Basically everything that happened in the universe is because of

705
00:33:22,840 --> 00:33:24,280
Speaker 2: gravitational imbalances.

706
00:33:24,480 --> 00:33:27,160
Speaker 1: M yeah, I definitely happen, and I definitely have a

707
00:33:27,360 --> 00:33:32,680
Speaker 1: mass imbalance in certain parts of my body. Gravity. Yeah,

708
00:33:32,720 --> 00:33:37,680
Speaker 1: it's all good. I'm blaeing the chocolate bars. So then,

709
00:33:37,720 --> 00:33:40,080
Speaker 1: but then, how does the mass of the galaxy affect

710
00:33:40,120 --> 00:33:43,080
Speaker 1: these bars? Like why would having more mass or less

711
00:33:43,120 --> 00:33:45,160
Speaker 1: mass affect the bar formation?

712
00:33:45,520 --> 00:33:49,320
Speaker 2: Because structure formation takes time, right, Gravity is very very weak,

713
00:33:49,640 --> 00:33:52,760
Speaker 2: and it takes time for gravity to overwhelm these other things.

714
00:33:52,800 --> 00:33:55,600
Speaker 2: It takes time for gravity to pull stars together, it

715
00:33:55,640 --> 00:33:58,520
Speaker 2: takes time for those stars to then influence each other.

716
00:33:58,840 --> 00:34:01,520
Speaker 2: So all these things take time, and lower mass galaxies

717
00:34:01,560 --> 00:34:03,720
Speaker 2: have less gravity, so it just takes them longer to

718
00:34:03,760 --> 00:34:06,880
Speaker 2: sort of come together and form these things. And structure

719
00:34:06,920 --> 00:34:10,479
Speaker 2: is sort of hierarchical, right, it's bottom up. You build

720
00:34:10,520 --> 00:34:13,000
Speaker 2: the stars, the stars build a galaxy, You build a

721
00:34:13,040 --> 00:34:15,719
Speaker 2: structure on that, and then you build structures on those structures.

722
00:34:16,120 --> 00:34:18,640
Speaker 2: The barred spiral galaxy is sort of like the pinnacle

723
00:34:18,680 --> 00:34:22,200
Speaker 2: of universal structure. It's like the most complex organized thing

724
00:34:22,239 --> 00:34:23,640
Speaker 2: the universe has made so far.

725
00:34:25,239 --> 00:34:27,279
Speaker 1: Well, it definitely sounds like we've raised the bar here

726
00:34:27,320 --> 00:34:29,920
Speaker 1: in terms of galactic mysteries. It seems like this is

727
00:34:29,960 --> 00:34:32,000
Speaker 1: still a question for many scientists, and in fact, it

728
00:34:32,120 --> 00:34:36,200
Speaker 1: might even have interesting consequences for our conception of dark

729
00:34:36,239 --> 00:34:39,560
Speaker 1: matter and how they influence the formation of these galaxies.

730
00:34:40,200 --> 00:34:43,520
Speaker 1: So let's dig into those dark matters. But first, let's

731
00:34:43,600 --> 00:34:59,920
Speaker 1: take another quick break. Right, we're talking about galactic bars now, Daniels,

732
00:35:00,000 --> 00:35:03,520
Speaker 1: this is where single stars go to meet other single stars.

733
00:35:05,520 --> 00:35:08,000
Speaker 2: This is where molecular clouds hang out hoping to one

734
00:35:08,040 --> 00:35:08,880
Speaker 2: day make stars.

735
00:35:09,600 --> 00:35:11,880
Speaker 1: They're like celebrity bars. You see a lot of stars

736
00:35:11,880 --> 00:35:13,680
Speaker 1: in them.

737
00:35:13,880 --> 00:35:15,400
Speaker 2: This is where stars are born. Baby.

738
00:35:15,640 --> 00:35:18,480
Speaker 1: All right, Well, we talked about how we're not quite

739
00:35:18,520 --> 00:35:21,160
Speaker 1: one hundred percent sure why some galaxies are bars. It

740
00:35:21,200 --> 00:35:24,200
Speaker 1: seems like it's just a matter of the physics, like

741
00:35:24,239 --> 00:35:27,319
Speaker 1: the weirdness of how stars and the gravity interact and

742
00:35:27,360 --> 00:35:30,719
Speaker 1: form ripples in a cluster of stars. But there is

743
00:35:30,760 --> 00:35:33,680
Speaker 1: sort of another component to it, which is dark matter. Right.

744
00:35:33,800 --> 00:35:36,440
Speaker 1: Dark matter plays a big role in how galaxies form,

745
00:35:37,200 --> 00:35:40,560
Speaker 1: how fast they form, what shapes they have, and so

746
00:35:40,640 --> 00:35:42,719
Speaker 1: what do these bars tell us about dark matter?

747
00:35:42,880 --> 00:35:46,160
Speaker 2: Yeah, you're exactly right. And remember that the stars themselves

748
00:35:46,200 --> 00:35:49,000
Speaker 2: are just like tracers that tell you where most of

749
00:35:49,040 --> 00:35:52,759
Speaker 2: the mass is in the universe. So most of the dynamics,

750
00:35:52,760 --> 00:35:56,000
Speaker 2: the gravitational forces, are hidden from us. We live in

751
00:35:56,000 --> 00:35:58,360
Speaker 2: a dark universe where we only see a tiny, little

752
00:35:58,360 --> 00:36:01,720
Speaker 2: fraction of what's going on out there. So by studying

753
00:36:01,719 --> 00:36:03,920
Speaker 2: the motion of the gas and the dust and the stars,

754
00:36:03,960 --> 00:36:06,040
Speaker 2: we could try to get a glimpse for what's going

755
00:36:06,080 --> 00:36:09,080
Speaker 2: on sort of behind the curtain. What the fuller picture

756
00:36:09,200 --> 00:36:11,960
Speaker 2: of the universe is, and you're absolutely right that dark

757
00:36:12,000 --> 00:36:14,799
Speaker 2: matter controls the formation of the galaxies. We wouldn't have

758
00:36:14,880 --> 00:36:17,560
Speaker 2: galaxies this early in the universe if it wasn't for

759
00:36:17,719 --> 00:36:20,640
Speaker 2: dark matter. Eighty percent of the matter in the universe

760
00:36:20,880 --> 00:36:23,319
Speaker 2: is dark matter, but more like ninety percent of the

761
00:36:23,360 --> 00:36:27,280
Speaker 2: matter in galaxies is dark matter. So galaxies are basically

762
00:36:27,440 --> 00:36:30,960
Speaker 2: mostly dark matter. And because dark matter feels gravity, it

763
00:36:31,000 --> 00:36:35,160
Speaker 2: has a huge influence on gravitational turbulence, like the formation

764
00:36:35,360 --> 00:36:36,000
Speaker 2: of bars.

765
00:36:36,040 --> 00:36:39,279
Speaker 1: Absolutely so, all this time that we've been talking about

766
00:36:39,280 --> 00:36:41,600
Speaker 1: the mass of a galaxy, I thought we were talking

767
00:36:41,640 --> 00:36:44,040
Speaker 1: about the stars, But are we also talking about the

768
00:36:44,160 --> 00:36:45,640
Speaker 1: mass due to dark matter.

769
00:36:45,760 --> 00:36:47,880
Speaker 2: Yeah, we're talking about the total mass, not just the

770
00:36:47,960 --> 00:36:49,360
Speaker 2: visible mass of the galaxy.

771
00:36:50,000 --> 00:36:52,520
Speaker 1: Or are they pretty correlated, like the more stars you

772
00:36:52,560 --> 00:36:55,359
Speaker 1: see in a galaxy, the more dark matter it has.

773
00:36:56,040 --> 00:36:58,800
Speaker 2: Yeah, great question. We did a podcast recently about the

774
00:36:58,880 --> 00:37:02,799
Speaker 2: variation of dark man matter in galaxies. Most galaxies have

775
00:37:02,960 --> 00:37:06,160
Speaker 2: around ninety percent of their mass is dark matter, but

776
00:37:06,200 --> 00:37:08,320
Speaker 2: there is a variation. There's some that are like ninety

777
00:37:08,400 --> 00:37:11,360
Speaker 2: nine percent dark matter and some that have almost none

778
00:37:11,520 --> 00:37:14,480
Speaker 2: or maybe zero dark matter. It tells a really fun

779
00:37:14,520 --> 00:37:16,840
Speaker 2: story about the history of galaxies and how they form

780
00:37:16,880 --> 00:37:19,239
Speaker 2: and merge and might even strip each other of dark

781
00:37:19,280 --> 00:37:22,279
Speaker 2: matter on the whole. There's a reasonable correlation, and like

782
00:37:22,400 --> 00:37:26,120
Speaker 2: ninety percent of a galaxy's mass is invisible ninety percent

783
00:37:26,600 --> 00:37:27,440
Speaker 2: ninety percent.

784
00:37:27,560 --> 00:37:31,200
Speaker 1: Yeah, but isn't like the proportion of the universe something

785
00:37:31,239 --> 00:37:33,439
Speaker 1: like five to one dark matter to normal matter.

786
00:37:33,560 --> 00:37:36,319
Speaker 2: Yeah, so galaxies tend to have more dark matter than

787
00:37:36,400 --> 00:37:37,400
Speaker 2: most of the universe.

788
00:37:38,200 --> 00:37:39,879
Speaker 1: Why is that? Is it just because there's a lot

789
00:37:39,880 --> 00:37:42,719
Speaker 1: of like stars and does kind of in between galaxies

790
00:37:42,719 --> 00:37:43,120
Speaker 1: out there.

791
00:37:43,239 --> 00:37:45,880
Speaker 2: It's because dark matter is really responsible for the formation

792
00:37:45,960 --> 00:37:48,960
Speaker 2: of galaxies, and once a galaxy forms, it's hard for

793
00:37:49,000 --> 00:37:51,480
Speaker 2: it to lose its dark matter, but it's possible for

794
00:37:51,520 --> 00:37:53,640
Speaker 2: it to lose its gas and its dust and even

795
00:37:53,719 --> 00:37:56,319
Speaker 2: its stars. There's all sorts of processes that tend to

796
00:37:56,320 --> 00:37:59,560
Speaker 2: blow out gas and dust from a galaxy, you know,

797
00:38:00,000 --> 00:38:03,319
Speaker 2: supernova or radiation from the central black hole. All these

798
00:38:03,320 --> 00:38:06,120
Speaker 2: things can push normal matter out of a galaxy, but

799
00:38:06,160 --> 00:38:09,200
Speaker 2: they don't affect its dark matter. So the dark matter

800
00:38:09,239 --> 00:38:11,960
Speaker 2: is sort of there in the background, forming the gravitational

801
00:38:11,960 --> 00:38:14,759
Speaker 2: structure on which the rest of the universe lives, and

802
00:38:14,800 --> 00:38:17,640
Speaker 2: it's much less influenced by everything else that happens to

803
00:38:17,719 --> 00:38:18,479
Speaker 2: the normal matter.

804
00:38:19,000 --> 00:38:21,800
Speaker 1: Okay, so if our galaxy is ninety percent dark matter,

805
00:38:22,160 --> 00:38:24,960
Speaker 1: I would think that was like the most powerful thing.

806
00:38:25,080 --> 00:38:27,759
Speaker 1: That term is the shape with a galaxy. So does

807
00:38:27,800 --> 00:38:31,279
Speaker 1: that mean that the dark matter in our galaxy is

808
00:38:31,320 --> 00:38:33,799
Speaker 1: also in a spiral shape and maybe also has a

809
00:38:33,840 --> 00:38:35,720
Speaker 1: bar of dark matter in the middle.

810
00:38:35,840 --> 00:38:37,960
Speaker 2: Yeah, great question. We don't know the answer to that

811
00:38:38,040 --> 00:38:40,680
Speaker 2: because we don't know the distribution of dark matter in

812
00:38:40,719 --> 00:38:43,760
Speaker 2: the galaxy with a lot of precision. We know roughly

813
00:38:43,800 --> 00:38:46,000
Speaker 2: that it's denser in the core and then it's spread

814
00:38:46,000 --> 00:38:49,040
Speaker 2: out like a big halo. But we also know something

815
00:38:49,080 --> 00:38:50,920
Speaker 2: about the physics of dark matter, like we know that

816
00:38:51,040 --> 00:38:54,560
Speaker 2: dark matter doesn't feel friction with other dark matter the

817
00:38:54,640 --> 00:38:57,160
Speaker 2: way normal matter does. Like two clouds of gas that

818
00:38:57,200 --> 00:39:00,640
Speaker 2: pass through each other will exchange energy them will tend

819
00:39:00,640 --> 00:39:03,160
Speaker 2: to fall towards the center for example. These kinds of

820
00:39:03,280 --> 00:39:05,920
Speaker 2: energy exchanges just don't happen for dark matter because dark

821
00:39:05,960 --> 00:39:09,160
Speaker 2: matter passes right through itself. It only feels gravity, and

822
00:39:09,160 --> 00:39:11,920
Speaker 2: gravity is not strong enough for those kinds of exchanges.

823
00:39:12,239 --> 00:39:15,440
Speaker 2: So the complex structures you see forming in normal matter

824
00:39:15,520 --> 00:39:18,120
Speaker 2: don't always happen in dark matter. That's why we think

825
00:39:18,200 --> 00:39:21,040
Speaker 2: dark matter is sort of a bigger, fluffier halo than

826
00:39:21,040 --> 00:39:23,200
Speaker 2: the more compact visible matter in the galaxy.

827
00:39:24,200 --> 00:39:27,439
Speaker 1: The shape of the regular stars is mostly due to gravity, right,

828
00:39:27,480 --> 00:39:30,360
Speaker 1: and dark matter feels gravity with itself, doesn't it.

829
00:39:30,120 --> 00:39:33,719
Speaker 2: It's mostly due to gravity, but also crucially relies on

830
00:39:34,080 --> 00:39:37,680
Speaker 2: losing energy. Like if stuff is just swirling around gravitationally,

831
00:39:37,880 --> 00:39:40,880
Speaker 2: it won't collapse nearly as easily if it's not sticky,

832
00:39:40,880 --> 00:39:43,480
Speaker 2: if it just passes right through itself. When things are

833
00:39:43,560 --> 00:39:46,600
Speaker 2: orbiting a black hole, for example, they could orbit there forever,

834
00:39:46,840 --> 00:39:48,600
Speaker 2: but they're much more likely to fall in if they

835
00:39:48,640 --> 00:39:51,200
Speaker 2: exchange some energy, so one of them gives up energy

836
00:39:51,239 --> 00:39:53,520
Speaker 2: to another one rather than passing right through.

837
00:39:53,880 --> 00:39:56,400
Speaker 1: You mean, like if the stuff swirling around crashes with

838
00:39:56,480 --> 00:39:59,560
Speaker 1: itself or like bumps into itself and it's going to

839
00:39:59,640 --> 00:40:00,400
Speaker 1: lose some energy.

840
00:40:00,880 --> 00:40:03,040
Speaker 2: Yeah, So things are just much more stable if there's

841
00:40:03,080 --> 00:40:07,200
Speaker 2: no interactions other than gravity. The other interactions, they tend

842
00:40:07,239 --> 00:40:09,680
Speaker 2: to exchange energy and then stuff can fall into the

843
00:40:09,719 --> 00:40:12,480
Speaker 2: center to make stars or to make galaxies, or to

844
00:40:12,480 --> 00:40:15,080
Speaker 2: make arms, this kind of stuff. But the truth is

845
00:40:15,120 --> 00:40:17,360
Speaker 2: we don't really know what structure there is to the

846
00:40:17,440 --> 00:40:19,440
Speaker 2: dark matter. We don't have a lot of great probes

847
00:40:19,719 --> 00:40:22,840
Speaker 2: for exactly where the dark matter is throughout the galaxy.

848
00:40:23,480 --> 00:40:25,360
Speaker 1: It could be a dark chocolate bar in the middle.

849
00:40:25,480 --> 00:40:28,720
Speaker 1: It could be just like a moose spread out throughout

850
00:40:28,719 --> 00:40:29,880
Speaker 1: the whole galaxy.

851
00:40:30,400 --> 00:40:32,560
Speaker 2: It could be We're getting better and better techniques to

852
00:40:32,640 --> 00:40:35,560
Speaker 2: map where the dark matter is in the galaxy, but

853
00:40:35,600 --> 00:40:38,000
Speaker 2: we don't have a very accurate picture. But you know,

854
00:40:38,120 --> 00:40:41,160
Speaker 2: simple models of the physics of dark matter tell us

855
00:40:41,160 --> 00:40:43,480
Speaker 2: how it should be distributed, though we don't know if

856
00:40:43,520 --> 00:40:45,080
Speaker 2: those models are accurate, of course.

857
00:40:45,640 --> 00:40:48,360
Speaker 1: But then in all these simulations you're talking about where

858
00:40:48,360 --> 00:40:50,920
Speaker 1: we are finding out all these things about the bars,

859
00:40:51,320 --> 00:40:54,120
Speaker 1: do they include dark matter in those simulations? And kauds

860
00:40:54,120 --> 00:40:55,520
Speaker 1: of assumptions do you have to make there?

861
00:40:55,760 --> 00:40:58,080
Speaker 2: They do include dark matter, and they treat dark matter

862
00:40:58,120 --> 00:41:01,640
Speaker 2: as like a collisionless fluid, like they're in the backdrop

863
00:41:01,680 --> 00:41:05,320
Speaker 2: of providing more gravity. And the dark matter does definitely

864
00:41:05,360 --> 00:41:08,799
Speaker 2: influence the formation of bars in these simulations. The more

865
00:41:08,920 --> 00:41:12,040
Speaker 2: dark matter you have, the less often you get a bar,

866
00:41:12,440 --> 00:41:15,040
Speaker 2: even when you have some sort of like gravitational instability

867
00:41:15,120 --> 00:41:17,240
Speaker 2: or over density in the visible matter.

868
00:41:17,520 --> 00:41:20,920
Speaker 1: So does dark matter help the bars or prevent the bars?

869
00:41:21,000 --> 00:41:24,040
Speaker 2: It prevents the bars from forming. So the more dark

870
00:41:24,080 --> 00:41:26,480
Speaker 2: matter you have, the more it tends to smooth out

871
00:41:26,560 --> 00:41:29,080
Speaker 2: the gravity of the disc, just like having a thicker

872
00:41:29,120 --> 00:41:31,120
Speaker 2: disc right, as you were saying earlier, sort of like

873
00:41:31,120 --> 00:41:34,280
Speaker 2: a two D effect. The more three d R galaxy becomes,

874
00:41:34,280 --> 00:41:36,880
Speaker 2: the less susceptible it is to these effects. In the

875
00:41:36,920 --> 00:41:40,480
Speaker 2: same way dark matter basically reduces the effect of gravity

876
00:41:40,480 --> 00:41:44,160
Speaker 2: of the visible matter provides this like background gravity pulling

877
00:41:44,200 --> 00:41:45,360
Speaker 2: on everything.

878
00:41:45,400 --> 00:41:48,560
Speaker 1: I see, like it evens out the strength of gravity

879
00:41:48,640 --> 00:41:51,400
Speaker 1: in the galaxy. Right, because you think dark matter is

880
00:41:51,440 --> 00:41:54,480
Speaker 1: distributed spread all over the place, the more significant that is,

881
00:41:54,520 --> 00:41:58,880
Speaker 1: the more generally speaking, gravity is in that galaxy exactly.

882
00:41:59,000 --> 00:42:01,200
Speaker 1: And so if you have no dark matter, do you

883
00:42:01,239 --> 00:42:01,920
Speaker 1: always get a bar?

884
00:42:02,080 --> 00:42:05,160
Speaker 2: Nothing happens every time in simulation, but the proportion definitely

885
00:42:05,160 --> 00:42:07,799
Speaker 2: goes up if you have no dark matter. But we

886
00:42:07,840 --> 00:42:10,080
Speaker 2: don't expect that to happen in the universe very often,

887
00:42:10,320 --> 00:42:12,560
Speaker 2: as we talked about recently on the podcast. We don't

888
00:42:12,600 --> 00:42:15,480
Speaker 2: think galaxies can form without dark matter, though they might

889
00:42:15,560 --> 00:42:18,640
Speaker 2: later be stripped of their dark matter in some collisions,

890
00:42:19,080 --> 00:42:21,239
Speaker 2: But then collisions are also going to destroy a bar.

891
00:42:22,120 --> 00:42:25,400
Speaker 1: So is the bar kind of a sign of how

892
00:42:25,480 --> 00:42:27,319
Speaker 1: much dark matter there is in a galaxy, then.

893
00:42:27,320 --> 00:42:30,080
Speaker 2: Yes, exactly. And people have used bars to try to

894
00:42:30,160 --> 00:42:33,319
Speaker 2: measure the dark matter fraction in galaxies. Like if you

895
00:42:33,320 --> 00:42:35,200
Speaker 2: look up at the night sky and you measure the

896
00:42:35,200 --> 00:42:38,120
Speaker 2: fraction of galaxies that have bars in them, that tells

897
00:42:38,120 --> 00:42:40,239
Speaker 2: you something about how much dark matter there can be

898
00:42:40,280 --> 00:42:42,960
Speaker 2: in those galaxies, because if there's a lot of dark

899
00:42:43,000 --> 00:42:45,960
Speaker 2: matter in all those galaxies, they wouldn't have bars, And

900
00:42:46,000 --> 00:42:48,200
Speaker 2: if there was less dark matter in those galaxies, more

901
00:42:48,239 --> 00:42:50,600
Speaker 2: of them would have bars. So we can actually use

902
00:42:50,680 --> 00:42:53,120
Speaker 2: the bars as a way to like indirectly estimate the

903
00:42:53,200 --> 00:42:55,799
Speaker 2: dark matter fraction of the universe in a way that's

904
00:42:55,840 --> 00:42:58,520
Speaker 2: separate from the galactic rotation speed or any of the

905
00:42:58,640 --> 00:42:59,320
Speaker 2: other probes.

906
00:43:00,160 --> 00:43:02,880
Speaker 1: Like the bar sets the bar for dark matter.

907
00:43:05,040 --> 00:43:07,799
Speaker 2: Yeah, it raises the bar on our understanding.

908
00:43:07,480 --> 00:43:09,680
Speaker 1: Our precision to measure dark matter.

909
00:43:10,280 --> 00:43:13,200
Speaker 2: Yeah, this is not a very precise measurement because we

910
00:43:13,239 --> 00:43:15,239
Speaker 2: don't have that many galaxies where we can measure this

911
00:43:15,360 --> 00:43:17,920
Speaker 2: kind of thing. But it's consistent with everything else we

912
00:43:18,000 --> 00:43:20,920
Speaker 2: know about dark matter. So the fraction of galaxies with

913
00:43:21,000 --> 00:43:24,239
Speaker 2: bars is consistent with our understanding that eighty percent of

914
00:43:24,280 --> 00:43:26,439
Speaker 2: the matter in the universe is dark matter, and something

915
00:43:26,480 --> 00:43:29,960
Speaker 2: like ninety percent of the matter in galaxies is dark matter.

916
00:43:31,520 --> 00:43:35,240
Speaker 1: And then what percentage is Hershey's chocolate versus snob chocolate.

917
00:43:36,840 --> 00:43:40,640
Speaker 2: I see, now you're disparaging people's choice chocolate. It goes

918
00:43:40,680 --> 00:43:47,600
Speaker 2: both ways. I'm all right, I can take it. If

919
00:43:47,600 --> 00:43:49,279
Speaker 2: I can dish it out, I can take it. That's fair.

920
00:43:49,640 --> 00:43:52,520
Speaker 2: I'm sure that Hershey's dominates the chocolate market, but I'm

921
00:43:52,560 --> 00:43:55,320
Speaker 2: glad that there are now a variety of chocolate offerings

922
00:43:55,320 --> 00:43:56,160
Speaker 2: for people to enjoy.

923
00:43:56,520 --> 00:43:59,480
Speaker 1: All right. Well, another interesting feature of our galaxy and

924
00:43:59,560 --> 00:44:01,800
Speaker 1: of our u universe the way physics works to create

925
00:44:01,840 --> 00:44:04,600
Speaker 1: these weird characteristics of the things we see out there,

926
00:44:04,640 --> 00:44:07,799
Speaker 1: which then kind of reveal what things are made of

927
00:44:07,880 --> 00:44:11,080
Speaker 1: and how things work in the grand cosmic scale things.

928
00:44:11,200 --> 00:44:13,360
Speaker 2: Absolutely, and it's just part of the game we're playing,

929
00:44:13,400 --> 00:44:15,759
Speaker 2: looking out at the night sky and out deep into

930
00:44:15,800 --> 00:44:18,000
Speaker 2: the universe to try to get a handle on what's

931
00:44:18,080 --> 00:44:21,640
Speaker 2: going on out there, what structures form, why do they form,

932
00:44:21,719 --> 00:44:24,239
Speaker 2: and what do they reveal about the flash of titanic

933
00:44:24,280 --> 00:44:26,439
Speaker 2: forces that's happening underneath it all.

934
00:44:26,920 --> 00:44:28,640
Speaker 1: It sounds like these bars are giving us a good

935
00:44:28,680 --> 00:44:33,600
Speaker 1: handle on galaxy formation and dark matter content of the Universe.

936
00:44:34,760 --> 00:44:36,480
Speaker 2: I'm going to go hit the lunch bar after this.

937
00:44:37,400 --> 00:44:42,600
Speaker 1: Yeah, just don't hit the dessert bar too hard. It

938
00:44:42,600 --> 00:44:44,879
Speaker 1: depends on the kind of chocolate ban Yeah, that's right.

939
00:44:44,920 --> 00:44:46,240
Speaker 1: The brand apparently.

940
00:44:48,520 --> 00:44:51,120
Speaker 2: Love all you and love all your chocolate choices. Keep

941
00:44:51,239 --> 00:44:54,600
Speaker 2: chomping on bars. That sounds really credible, Daniel. I'm working

942
00:44:54,600 --> 00:44:55,960
Speaker 2: on it, man, I'm working on it all right.

943
00:44:56,000 --> 00:44:58,239
Speaker 1: Well, we hope you enjoyed that. Thanks for joining us.

944
00:44:58,840 --> 00:44:59,600
Speaker 1: See you next time.

945
00:45:04,120 --> 00:45:07,320
Speaker 2: For more science and curiosity, come find us on social media,

946
00:45:07,400 --> 00:45:11,920
Speaker 2: where we answer questions and post videos. We're on Twitter, Discorg, Insta,

947
00:45:12,040 --> 00:45:15,760
Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel

948
00:45:15,800 --> 00:45:19,240
Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.

949
00:45:19,520 --> 00:45:24,640
Speaker 2: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,

950
00:45:24,800 --> 00:45:27,160
Speaker 2: or wherever you listen to your favorite shows.