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Speaker 1: Gravity is a monster. Not the kind of monster that

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Speaker 1: jumps out and slashes you. It's the kind that shuffles slowly,

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Speaker 1: never racing, but always getting closer. It's patient, happy to

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Speaker 1: wait billions of years until everyone else has had their turn.

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Speaker 1: But it never ever ever gives up. It's always there,

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Speaker 1: ready to tear you to shreds or crush you into

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Speaker 1: a speck. And in the end, it's gravity that dominates

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Speaker 1: our cosmic destiny. We rely on quantum forces, like the

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Speaker 1: structural integrity of the Earth or the radiation pressure from

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Speaker 1: fusion that keeps the Sun from collapsing. They keep gravity

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Speaker 1: at bay for now, but inevitably they will fail us,

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Speaker 1: and gravity will overcome each of our defenses, making white

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Speaker 1: dwarves and neutron stars, and eventually victorious in creating black holes,

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Speaker 1: Gravity's ultimate trophies. But where exactly is the quantum limit?

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Speaker 1: How close can one get to the black hole threshold

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Speaker 1: without collapsing? What is the last line of quantum defense

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Speaker 1: against the plotting unavoidable onslaught of the gravitational monster. We'll

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Speaker 1: dig into all of that on today's episode. Welcome to

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Speaker 1: Daniel and Kelly's extraordinarily crushing universe.

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Speaker 2: Hello.

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Speaker 3: I'm Kelly winder Smith. I study parasites and space, and

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Speaker 3: today we're going to learn that physicists love noodles. Where

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Speaker 3: do you go from there, Daniel?

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

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Speaker 1: worship at the arm of his newly appendage.

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Speaker 3: Oh man, that is a throwback. I feel like the

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Speaker 3: Pastafarians were a big deal when I was an undergrad

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Speaker 3: and master student.

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Speaker 1: Raw men brother ram, Oh my gosh, I.

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Speaker 3: Never heard that. Okay, all right, so let's go way back.

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Speaker 3: So I'm wondering what young physicist Daniel was, like, what

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Speaker 3: is the first science project you did? And I'm thinking,

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Speaker 3: like science fairies when you were a kid.

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Speaker 1: Ooh, that's a great question, and I think it's kind

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Speaker 1: of revealing, but not very romantic. Actually, young physicist Daniel

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Speaker 1: had no idea what physics was actually like and was

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Speaker 1: doing it because number one, I seem to be good

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Speaker 1: at it, and number two people told me it was hard,

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Speaker 1: and I was like, I don't really understand how the

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Speaker 1: world works, and I'm kind of confused and socially awkward,

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Speaker 1: but this is something I'm good at that people seem

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Speaker 1: to like. So I'll just do that for a while.

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Speaker 1: And honestly, my sincere just in physics wasn't really kindled

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Speaker 1: until pretty late in undergrad when I found particle physics

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Speaker 1: and I realized, oh, my gosh, physics can actually be fun.

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Speaker 1: Research can be something that touches a passion deep inside you.

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Speaker 1: I was going through the motions for a long long time,

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Speaker 1: including my first ever science project, which was an experiment

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Speaker 1: to measure how much light mirrors absorb. So we took

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Speaker 1: a little laser beam and we bounced it back and

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Speaker 1: forth between some mirrors. Then we had a censor at

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Speaker 1: the end, and I measure the intensity of the light

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Speaker 1: after a bunch of bounces and before, and did it

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Speaker 1: as a function of the number of bounces, and so

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Speaker 1: from that you can extract the fraction of the light

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Speaker 1: that's absorbed by every bounce in the mirror.

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Speaker 2: Whoa cool?

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Speaker 3: What year was that?

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Speaker 1: It was pretty cool? I think I was in middle school,

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Speaker 1: and you know, it didn't take any fancy math or

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Speaker 1: any fancy equipment. But I remember the judge being like,

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Speaker 1: did your dad do this experiment? I was like, what

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Speaker 1: which part do I need him for? Like the dividing

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Speaker 1: the count It's just like a pen laser and a

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Speaker 1: couple of mirrors. But I had a lot of fun.

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Speaker 1: I thought it was really cool because I didn't realize

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Speaker 1: until then the mirrors don't perfectly reflect. They do absorb

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Speaker 1: some light.

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Speaker 3: So your hypothesis was that you were going to get

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Speaker 3: the exact same value from the laser as you got

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Speaker 3: after it bounced.

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Speaker 1: I was curious it was measurable. I thought maybe I

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Speaker 1: was going to get something where it was like nine percent,

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Speaker 1: But it turns out to be mirrors are quite absorbent.

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Speaker 1: I mean, you can't use them to wipe up your

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Speaker 1: kitchen or anything, but they do they do drink some light.

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Speaker 1: How about you, Kelly, what was your first ever piece

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Speaker 1: of science data?

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Speaker 3: Yeah, so I Kelly, did not look like a promising scientist.

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Speaker 3: In sixth grade for the first science fair, I put

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Speaker 3: the project off until the last second, and it was

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Speaker 3: like a couple of days beforehand. And I was into

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Speaker 3: like conservation and protecting the environment, but I didn't really

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Speaker 3: know how to do science, and so I pretty much

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Speaker 3: like took a tiny little fish bowl and I stole

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Speaker 3: some motor oil from the garage, and I like dumped

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Speaker 3: it in and I was like, that doesn't look good.

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Speaker 3: Oil spills are bad.

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Speaker 1: That was no whole project, and what was the hypothesis?

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Speaker 1: Is oil? Icky? Answer?

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Speaker 3: Yes, uh yeah, I don't actually think I had a hypothesis.

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Speaker 3: I was just like, gross, that's not good. And I

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Speaker 3: remember getting a pretty uh negative review from my teacher

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Speaker 3: who was get you know, who probably pointed out that

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Speaker 3: there was no hypothesis being tested here. Kelly just dumped

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Speaker 3: some oil and water and brought that to school and

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Speaker 3: uh so, so anyway, I appeared pretty dense as a

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Speaker 3: sixth grader, and today we're going to be talking about

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Speaker 3: dense things.

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Speaker 1: Ooh wow, what a crushing transition. Nice job, thank.

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Speaker 3: You, thank you. I planned ahead. Well.

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Speaker 1: The crushing power of gravity is fascinating and one of

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Speaker 1: the enduring mysteries of physics. How does it work? How

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Speaker 1: do we interface it with quantum mechanics? Is Einstein's theory

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Speaker 1: real or is it just some weird emergent approximation of

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Speaker 1: something else that's happening deep down? And the best way

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Speaker 1: to get the answers to those questions are the places

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Speaker 1: where gravity and quantum mechanics connect, where gravity is so

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Speaker 1: extreme it can actually overcome quantum forces. So that means

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Speaker 1: thinking about black holes and how they form and how

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Speaker 1: basically the whole universe inevitably is going to collapse into

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Speaker 1: a black hole. And that means you and everything.

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Speaker 3: You love ah existential dread, my old friends that that

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Speaker 3: friend tends to visit more when Daniel's are.

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Speaker 1: Out, But you know, it's existential dread with a life

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Speaker 1: sprinkling of dad jokes and mom.

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Speaker 3: Jokes yay and knowledge right.

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Speaker 1: And something that's always fascinated me about this question is

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Speaker 1: that we can resist gravity sort of temporarily. We're like

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Speaker 1: a weightlifter holding some crushing weight above our heads, but

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Speaker 1: our knees are shaking and our thighs are vibrating, and

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Speaker 1: eventually you know you're going to drop that weight, but

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Speaker 1: you can for a while. And what's really fascinating to

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Speaker 1: me about holding off gravity is that we have these

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Speaker 1: series of defenses, these places where chemistry and quantum mechanics

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Speaker 1: pushes back. But I've always wondered, what is the last

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Speaker 1: line of defense, What is the densest thing that can

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Speaker 1: exist in our universe that hasn't quite yet given up

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Speaker 1: the ghost to gravity?

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Speaker 3: Oh, and when it gives up, it becomes a black hole.

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Speaker 1: Right, Okay, I've learned something that's surrender. Becoming a black

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Speaker 1: hole is surrender?

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Speaker 3: All right? Well, that is a fantastic question. I honestly

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Speaker 3: don't know the answer, but let's see if our extraordinaries

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Speaker 3: know the answer.

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Speaker 1: Thanks very much to everyone who participates, and if you

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Speaker 1: would like to join this elite crew of speculators, please

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Speaker 1: write to us two questions at Danielankelly dot org. So

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Speaker 1: think about it for a minute yourself. What do you

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Speaker 1: think is the densest thing that can exist in the

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Speaker 1: universe that's not a black hole?

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Speaker 4: Outside of black holes? I always thought that neutron stars

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Speaker 4: were the densest things in the universe, but I guess

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Speaker 4: we could also say the core of a neutron star

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Speaker 4: would be the densest thing. Of course, given you're asking,

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Speaker 4: it's probably neither of those dnsiest thing that's a black hole,

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Speaker 4: that would be.

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Speaker 2: Neutron star. It should be a neutron star.

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Speaker 3: I know those are the dancest objects in the universe

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Speaker 3: which are not black holes. Either a neutron star, a

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Speaker 3: movie by David Lynch, or does chocolate cake come about

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Speaker 3: to it? I like science, so I know a few

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Speaker 3: things and I can easily say confidently that the dentsst

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Speaker 3: thing not a black hole would be a neutron star.

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Speaker 2: Is the densest thing that's not a black hole, a

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Speaker 2: neutron star, like a sun that died and didn't become

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Speaker 2: a black hole because it was too small, so it

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Speaker 2: came a neutron star. Maybe a neutron star spinning like

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Speaker 2: a nine percent speed of light for some reason, just

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Speaker 2: because it seems I can give it a little more,

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Speaker 2: get up and go.

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Speaker 3: Well, Daniel, it sounds like the answer is neutron star.

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Speaker 3: Shortest episode yet, Thanks for Thanks for playing.

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Speaker 1: Everyone, And this is why science is not democratic, right,

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Speaker 1: just boat on stuff and move on. But it's cool

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Speaker 1: that everybody's heard about neutron stars and they know the

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Speaker 1: neutron stars are dense. But spoiler alert, neutron stars are

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Speaker 1: not the theoretically most dense objects in the universe.

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Speaker 3: What okay, wait, and so just to clarify, you said theoretically,

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Speaker 3: So at the end of the day, we're going to

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Speaker 3: be talking about what we think might be the most

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Speaker 3: dense thing next to black holes, but we're not totally sure,

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Speaker 3: is that right?

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Speaker 1: Stick around for the end and you'll find out.

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Speaker 3: I'm here for it. Let's do this all right. So you,

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Speaker 3: before we started going to the listener responses, you were

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Speaker 3: talking about how, you know, like a person holding up

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Speaker 3: a weight, and I guess I really when I did

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Speaker 3: CrossFit for a while, I really loved weightlifting. I totally

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Speaker 3: miss it. But anyway, so like a person trying to

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Speaker 3: hold up a heavyweight, they're you know, shaking and quaking

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Speaker 3: and they're pushing back against the weight before they collapse.

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Speaker 3: What is the equivalent for a star? Why doesn't it

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Speaker 3: just collapse?

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Speaker 1: I love that in this analogy, Kelly, is all of

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Speaker 1: QUI forces holding back gravity. What's the heaviest thing you

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Speaker 1: were ever able to lift?

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Speaker 3: Kelly, I don't remember what my pr was is that

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Speaker 3: I think that stood for personal record. I just know

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Speaker 3: that I really liked taking heavy stuff from the ground

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Speaker 3: and then putting it over my head. I thought that

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Speaker 3: was great.

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Speaker 1: Well, there is something very satisfying about that, because you're

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Speaker 1: overcoming gravity, and stars when they collapse, they collapse due

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Speaker 1: to gravity. But before we dig into that, let's just

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Speaker 1: remind ourselves the basics of gravity and why black holes

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Speaker 1: are inevitable. Gravity is one of the fundamental forces but

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Speaker 1: it's different from the other fundamental forces. It's not a

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Speaker 1: quantum force. We don't have a quantum explanation for it.

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Speaker 1: And it's also different because it's super duper weak. So

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Speaker 1: if you compare these things equivalently, like look at the

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Speaker 1: forces between two protons, gravity is like ten to the

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Speaker 1: thirty times weaker than any of the other fundamental forces,

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Speaker 1: and so you might think, well, gravity should be relevant, right.

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Speaker 1: It's like if you're balancing your checkbook and one expect

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Speaker 1: is like ten to the thirty times smaller than the others,

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Speaker 1: you can basically ignore it and still get the answer

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Speaker 1: right to the penny. Right. But the thing about gravity

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Speaker 1: is that it's inevitable because it cannot be canceled out.

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Speaker 1: Gravity is only an attractive force. Masses only get pulled together.

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Speaker 1: There is no repulsive gravity. I mean, there is expansion

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Speaker 1: in the universe, which we don't quite understand entirely, but

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Speaker 1: the force of gravity and over short distances can only

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Speaker 1: attract things, which means that it can't be neutralized. For example,

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Speaker 1: particles feel very strong electromagnetic forces, but then those are

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Speaker 1: rapidly neutralized when they form neutral atoms, and hydrogen doesn't

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Speaker 1: feel electromagnetic forces anymore. So vast clouds of hydrogen only

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Speaker 1: feel gravity. Gravity is inevitable because it cannot be neutralized

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Speaker 1: because it's only attractive.

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Speaker 3: All right, So let's see if I've absorbed all of that.

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Speaker 3: So you said that gravity is only attractive, but you

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Speaker 3: also mentioned that the universe is expanding, and we don't

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Speaker 3: really know why that does seem to be overcoming gravity.

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Speaker 3: So does does that mean, as we understand it right now,

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Speaker 3: gravity is only attractive, or does the expansion of the

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Speaker 3: universe just suggest that we understand gravity, but something different

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Speaker 3: is happening that's overcoming gravity because it's such a whim.

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Speaker 1: Yeah, we don't really understand the expansion of the universe,

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Speaker 1: especially it's accelerating expansion, and that can overcome gravity, but

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Speaker 1: only we're very very large distances, like between galactic superclusters,

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Speaker 1: where gravity gets weak because the distances are large. Over

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Speaker 1: smaller distances like the cluster of our galaxy, gravity overwhelms

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Speaker 1: dark energy or the expansion of the universe and holds

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Speaker 1: things together. That's why, even though the universe is expanding,

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Speaker 1: you're not flying apart, or our solar system is not

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Speaker 1: flying apart, or our galaxy is not flying apart. So

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Speaker 1: while it's inevitable for things to collapse into a black hole,

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Speaker 1: it's not going to be one huge, single universe black hole.

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Speaker 1: It's like every little neighborhood where gravity dominates is going

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Speaker 1: to pull everything together into a black hole eventually.

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Speaker 2: Okay.

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Speaker 3: And then just to remind me where we are with gravity,

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Speaker 3: we haven't found like gravity fields or anything. We don't

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Speaker 3: really kind of understand what's happening with gravity, but we

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Speaker 3: can very clearly measure it, and we know that it's

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Speaker 3: like a definite thing.

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Speaker 1: We have an excellent classical theory of gravity that ignores

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Speaker 1: quantum mechanics but makes perfect predictions everywhere we can test it.

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Speaker 1: So it's an excellent theory, but we think it's probably wrong.

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Speaker 3: All right, Well, at least it's helpful, okay.

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Speaker 1: But because gravity can't be canceled out the way like

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Speaker 1: electromagnetism can, you can't make an object which is neutral

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Speaker 1: in gravity eventually, even though it's weak, it's the only

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Speaker 1: thing left on the playground. So like, that's why the

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Speaker 1: structure of the Solar System is mostly due to gravity.

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Speaker 1: The structure or the galaxies mostly due to gravity. The

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Speaker 1: weakest force but everything else gets canceled out because they're

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Speaker 1: so powerful and because they have like positive and negative charges. Equivalently,

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Speaker 1: gravity basically only has positive charges, and so things only

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Speaker 1: attract and so it's the only thing left over. It

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Speaker 1: can't be neutralized, which is why gravity, though it's super weak,

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Speaker 1: shapes the cosmos.

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Speaker 3: That's interesting. I hadn't thought of gravity as being the

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Speaker 3: like winning worse because everything else canceled out. I thought

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Speaker 3: of gravity as being the winning force because there's just

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Speaker 3: so much mass.

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Speaker 1: Well, it's not hard to overcome gravity. Like you can

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Speaker 1: overcome gravity with your legs, right, you hold up those

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Speaker 1: enormous Kelly pr weights and the whole Earth is pulling

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Speaker 1: on them, and you're overcoming them with your like admitted

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Speaker 1: the impressive muscles. But you know you're small compared to

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Speaker 1: the Earth, yet you're still able to overcome its gravity.

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Speaker 1: And so that's an example. The quantum forces of your

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Speaker 1: muscles et are resisting gravity, and you can do that temporarily,

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Speaker 1: but you can't hold that weight up forever. And eventually,

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Speaker 1: if you add enough mass, gravity can overcome any quantum force.

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Speaker 1: It can pull stuff together and eventually collapse into a

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Speaker 1: black hole and that's sort of the destiny of everything

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Speaker 1: in the universe. But we can hold it off temporarily,

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Speaker 1: Like our Sun is not yet collapsing into a black hole.

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Speaker 3: And what is the Sun's equivalent of my massive bulging

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Speaker 3: rippling muscles? What is what is keeping things from collapsing.

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Speaker 1: Yeah, it's an amazing story because the beginning of the

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Speaker 1: life of a star is gravitational. You have these vast

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Speaker 1: clouds of hydrogen and dust and grains from previous stars, etc.

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Speaker 1: And a little bit of gravitational over density somewhere in

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Speaker 1: that cold cloud has to be like ten to twenty

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Speaker 1: Calvin will start a collapse. It will create a region

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Speaker 1: of higher density there for higher gravity, the pole stuff

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Speaker 1: which makes higher density, which means higher gravity. And you

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Speaker 1: get this runaway effect where you get a huge accumulation.

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Speaker 1: You start from very very low density cloud into a

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Speaker 1: very high density object a protostar. And what stops the

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Speaker 1: collapse is quantum mechanics, is fusion. You get such a

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Speaker 1: high density at the core of this star that the

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Speaker 1: temperature goes up because of all the pressure from the

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Speaker 1: outer layers. And when you have high temperature and high

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Speaker 1: pressure and you have protons, they start to fuse, and

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Speaker 1: that emits light. It releases energy, and that energy comes

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Speaker 1: out as photons. We call this radiation pressure. So fusion

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Speaker 1: ignites when the star gets big enough to get hot enough,

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Speaker 1: and that balances the star. So you have this initial

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Speaker 1: rush in due to gravity, and then fusion stands up

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Speaker 1: and says, hold on a second, I'm going to burn

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Speaker 1: for a little bit here, And for millions or billions

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Speaker 1: of years, the star is incredibly in balance where the

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Speaker 1: radiation pressure sort of cancels out the force of gravity,

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Speaker 1: and the star is able to hang out there and

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Speaker 1: just like emit light for billions of years.

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Speaker 3: And is it like amazing that they balance out or

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Speaker 3: does it make sense that they balance out because the

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Speaker 3: amount of fusion happening is like proportional to the extent

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Speaker 3: that it's getting squeezed.

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Speaker 1: It's sort of amazing to me that it balances out

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Speaker 1: and that it can balance for so long that the

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Speaker 1: balance is stable for billions of years. I can imagine

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Speaker 1: lots of other settings on the universe knobs where stars

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Speaker 1: are very very brief, right, And in our universe, the

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Speaker 1: length of star burns depends on its size. So, for example,

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Speaker 1: if you get a really really big star like early universe,

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Speaker 1: we think we had collapses of matter like two hundred

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Speaker 1: times the mass of the Sun. Well, the bigger the star,

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Speaker 1: the more massive it is, the more gravitational pressure you have,

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Speaker 1: the higher the temperature of the core, and fusion is

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Speaker 1: very sensitive to temperature, so as the temperature goes up,

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Speaker 1: the rate of fusion increases dramatically. So counterintuitively, a bigger

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Speaker 1: star doesn't last longer because it has more fuel. It

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Speaker 1: lasts much shorter because it burns that fuel at a

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Speaker 1: much higher temperature and it burns through it much more quickly.

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Speaker 1: So super huge stars only last a few million years,

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Speaker 1: whereas tiny stars can last for like many many billions

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Speaker 1: of years, longer than the age of the universe. We think, Wow,

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Speaker 1: our star is slightly on the bigger end. We think

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Speaker 1: its life cycle is going to be about ten billion years,

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Speaker 1: but red dwarves can last for much much longer. Small

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Speaker 1: cold stars just above that fusion threshold can be in

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Speaker 1: balance for billions and billions and billions of years.

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Speaker 3: Amazing, it's incredible. We've had conversations where I've learned that

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Speaker 3: mass is more complicated than I thought it was. When

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Speaker 3: you talk to a physicist, does density require some similar

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Speaker 3: unpacking or does density for a Physicists pretty much mean

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Speaker 3: what we sort of imagine it.

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Speaker 1: You mean, how we like sneakily redefined density to mean

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Speaker 1: something else and not means you didn't keep using the

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Speaker 1: same word. We would never do that, except we do

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Speaker 1: it all the time. Yes, you would, Yes, And we're

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Speaker 1: gonna do that with the word pasta later on. No,

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Speaker 1: density means the same thing. It's mass over volume. But

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Speaker 1: again counterintuitively, the densities of stars is sort of surprising,

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Speaker 1: Like the smaller stars red dwarfs are actually much denser

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Speaker 1: than the bigger stars. So to calibrate, water is a

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Speaker 1: thousand kilograms per cubic meter, that's the density, that's its density,

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Speaker 1: and the Earth is like five times that, So like

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Speaker 1: five thousand kilograms per cubic meter, a red dwarf is

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Speaker 1: like fifty to two hundred times that density, much much

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Speaker 1: denser than the earth or water at the core. And

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Speaker 1: you might expect that it's the opposite, right, that smaller

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Speaker 1: stars are less dense because they're not as hot and

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Speaker 1: there's not as much pressure at the core. But the

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Speaker 1: bigger stars that burn hotter, they're creating a lot more

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Speaker 1: radium pressure, so they puff the star out. So the Sun,

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Speaker 1: for example, has a density of like one to two

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Speaker 1: thousand kilograms per cubic meter. That's like about the density

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Speaker 1: of water.

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Speaker 3: I could float on the Sun. I mean I die,

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Speaker 3: but I could float a little.

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Speaker 1: We are not doctors. We do not recommend that you

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Speaker 1: take a swan dive into the Sun. But in principle, yes,

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Speaker 1: it isn't the density that would kill you.

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Speaker 3: That's right, something else would.

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Speaker 1: But it's weird to think about the density of the

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Speaker 1: Sun being density of water. But as you go to

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Speaker 1: bigger stars, hotter stars, like blue giants, they have a

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Speaker 1: density less than water, like two hundred to five hundred

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Speaker 1: kilograms per cubic meters. That's like the density of our atmosphere.

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Speaker 3: Okay, so bigger stars are less dense.

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Speaker 1: Yeah?

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Speaker 3: Is that because if a big star was more dense,

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Speaker 3: it would squish down. Yet, why couldn't you have I

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Speaker 3: think I'm still not quite following why you couldn't have

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Speaker 3: a really big dense star. What apps prohibits that from happening.

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Speaker 1: If you have a really big dense star, then it's

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Speaker 1: going to have an incredibly high temperature and fusion is

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Speaker 1: going to be super intense and it's going to blow

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Speaker 1: that star out, okay, And so gravitationally nothing prevents you

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Speaker 1: from having a big, dense star, but the quantum mechanics

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Speaker 1: of that star are going to push back. And that's

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Speaker 1: what happens. You can't have a star that's stable, that's

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Speaker 1: that big and that dense.

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Speaker 3: Okay, got it, totally makes sense. It's stuck in my

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Speaker 3: head now for now.

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Speaker 1: So that's about as dense as we can get with

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Speaker 1: actively burning stars because of the fusion. Right, here's quantum

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Speaker 1: mechanics pushing back on gravity. But that requires having fusion

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Speaker 1: at the core. And sometimes you get objects of form

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Speaker 1: that can't fuse, and so you might wonder could they

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Speaker 1: be even denser than stars?

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Speaker 3: And that question would keep me up at night, But

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Speaker 3: fortunately you are going to have an answer after the break,

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Speaker 3: all right, Daniel. So fusion is the rippling muscles of

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Speaker 3: the universe pushing back against gravity. But what happens when

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Speaker 3: you don't have fusion.

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Speaker 1: Yeah, we talked about the collapse of stars, and you

404
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Speaker 1: have these huge Maluculier clouds that collapse, but you get

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Speaker 1: lots of different collapses, right, You get a cloud doesn't

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00:21:28,119 --> 00:21:30,879
Speaker 1: collapse just into one star has lots of different stars

407
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Speaker 1: at different masses, and sometimes you get stars whose mass

408
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Speaker 1: is too small to raise the internal temperature to the

409
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Speaker 1: level of fusion. Right, So, like below, a red dwarf

410
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Speaker 1: is something we call a brown dwarf, something that has

411
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Speaker 1: less than eighty times the mass of Jupiter doesn't reach

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Speaker 1: the internal temperature to begin fusion. And this is also

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Speaker 1: true of like Jupiter itself or Earth. Right, Earth is

414
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Speaker 1: a big blob of stuff. It's hot at the core,

415
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Speaker 1: it's not hot enough to fuse, and that's why planets

416
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Speaker 1: can get denser than stars.

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Speaker 3: Oh and so does that have a bit to do

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Speaker 3: with what the insides are made of and like whether

419
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Speaker 3: it's good fusion material or not, or is it all

420
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Speaker 3: just about like how freshed it gets and how hot

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Speaker 3: that makes things.

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Speaker 1: All of those things what comes into play is what

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Speaker 1: it's made out of. And also it's structural integrity. Right, So,

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Speaker 1: we don't have fusion to protect the planet from collapsing

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Speaker 1: into a black hole. But the Earth is not collapsing

426
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Speaker 1: into a black hole right now as far as we know.

427
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Speaker 1: Why is that? Right? Well, what's saving the Earth is

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Speaker 1: chemistry actually, so thank you to chemistry.

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Speaker 3: Because man, it's a dark day for you and me.

430
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Speaker 1: I mean, we don't have to understand it, but we

431
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Speaker 1: can be grateful for it. But you know, all of

432
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Speaker 1: those atoms on the inside of the Earth are resisting

433
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Speaker 1: being collapsed by gravity. They have these forces between them,

434
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Speaker 1: the Vanderwall's forces and the electric repulsion, and they form

435
00:22:51,720 --> 00:22:55,680
Speaker 1: bonds and those things are still more powerful than gravity.

436
00:22:55,880 --> 00:22:57,960
Speaker 1: But yeah, the density of the planet depends on what

437
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Speaker 1: they're made out of. And again, the dense is sort

438
00:23:00,640 --> 00:23:04,040
Speaker 1: of counterintuitive. You'd be hard pressed to guess. For example, Kelly,

439
00:23:04,200 --> 00:23:05,919
Speaker 1: what do you think is the densest planet in the

440
00:23:05,960 --> 00:23:13,960
Speaker 1: Solar System? Bitter Although you sound so confident, but.

441
00:23:14,560 --> 00:23:16,680
Speaker 3: You know, you just told me that the big suns

442
00:23:16,760 --> 00:23:18,959
Speaker 3: are the least dense, and so now I'm wondering if

443
00:23:19,000 --> 00:23:20,840
Speaker 3: something similar is happening with the planets. But I think

444
00:23:20,880 --> 00:23:23,040
Speaker 3: probably not. So I'm gonna say Jupiter.

445
00:23:23,680 --> 00:23:25,800
Speaker 1: Well you double counterintuitive yourself.

446
00:23:26,080 --> 00:23:28,879
Speaker 3: Oh man, wait, so Venus Venus is like has a

447
00:23:28,880 --> 00:23:30,480
Speaker 3: lot of lead, Maybe it's Venus.

448
00:23:31,880 --> 00:23:34,480
Speaker 1: Well, both directions are actually wrong. You might think I'm

449
00:23:34,480 --> 00:23:37,439
Speaker 1: going to go for the biggest mass like Jupiter, but

450
00:23:37,680 --> 00:23:40,840
Speaker 1: Jupiter has created a huge amount of gas. Right, it's

451
00:23:40,880 --> 00:23:43,560
Speaker 1: a massive planet because it gobbled a lot of gas,

452
00:23:43,640 --> 00:23:45,560
Speaker 1: and in the early formation of the Solar System, it's

453
00:23:45,600 --> 00:23:48,400
Speaker 1: out beyond the snow line, and so it can accumulate

454
00:23:48,480 --> 00:23:51,440
Speaker 1: not just rock and metal, but also ice. And so

455
00:23:51,520 --> 00:23:53,840
Speaker 1: we don't have a perfect theory for how these giant

456
00:23:53,840 --> 00:23:56,639
Speaker 1: planets form, but one of the leading theories is that

457
00:23:56,680 --> 00:23:59,359
Speaker 1: they start from like a gravitational over density, like a

458
00:23:59,359 --> 00:24:02,200
Speaker 1: mini version of a solar collapse, and then they grab

459
00:24:02,359 --> 00:24:04,320
Speaker 1: the rest of the gas in the outer Solar System.

460
00:24:04,320 --> 00:24:06,520
Speaker 1: But because there's a lot of hydrogen there, it's not

461
00:24:06,720 --> 00:24:09,840
Speaker 1: actually that dense. So then you think, well, what about

462
00:24:09,880 --> 00:24:13,280
Speaker 1: an inner Solar system. Inner Solar system, all the water

463
00:24:13,400 --> 00:24:15,919
Speaker 1: is vaporized and all the gas is either gobbled by

464
00:24:15,960 --> 00:24:19,200
Speaker 1: the Sun or blown out by the Sun's early radiation,

465
00:24:19,280 --> 00:24:22,040
Speaker 1: and so you're left with things like iron and rock,

466
00:24:22,400 --> 00:24:24,760
Speaker 1: and like that's mostly what the Earth is made out of, right,

467
00:24:25,119 --> 00:24:27,600
Speaker 1: iron and rock and all sorts of crazy heavy dense

468
00:24:27,640 --> 00:24:31,040
Speaker 1: stuff like that. And mercury actually has the highest percentage

469
00:24:31,080 --> 00:24:34,000
Speaker 1: of these heavy elements, like eighty five percent of the

470
00:24:34,000 --> 00:24:36,879
Speaker 1: interior of mercury is a metallic core, compared to just

471
00:24:36,920 --> 00:24:40,119
Speaker 1: fifty five percent for Earth. Mercury has like a very

472
00:24:40,240 --> 00:24:41,320
Speaker 1: very thin mantle.

473
00:24:41,640 --> 00:24:44,880
Speaker 3: I think the lesson here is never go with Kelly's intuition.

474
00:24:46,440 --> 00:24:49,040
Speaker 1: But mercury is also not the densest planet in the

475
00:24:49,080 --> 00:24:51,480
Speaker 1: Solar system, right. The densest planet in the Solar System

476
00:24:51,520 --> 00:24:54,359
Speaker 1: is actually Earth because you have a balance here. In

477
00:24:54,440 --> 00:24:57,000
Speaker 1: order to get density, you need gravity to make it dense.

478
00:24:57,000 --> 00:24:59,160
Speaker 1: And so a mercury that has a lot of metal

479
00:24:59,200 --> 00:25:02,160
Speaker 1: in it doesn't have enough mass to compress the core

480
00:25:02,240 --> 00:25:05,439
Speaker 1: to get to the same density that Earth has. And

481
00:25:05,480 --> 00:25:08,560
Speaker 1: so you can take mercury, for example, and add to it,

482
00:25:08,680 --> 00:25:11,840
Speaker 1: add more stuff to it, and it's radius grows, but

483
00:25:11,960 --> 00:25:14,760
Speaker 1: also the pressure grows, so it gets more collapsed, and

484
00:25:14,840 --> 00:25:17,320
Speaker 1: so it becomes denser and denser. And this is actually

485
00:25:17,400 --> 00:25:20,800
Speaker 1: sort of a maximum size to a rocky planet, which

486
00:25:20,840 --> 00:25:24,200
Speaker 1: is about the radius of ten thousand kilometers, not much

487
00:25:24,200 --> 00:25:26,840
Speaker 1: bigger than Earth. If you took Earth and you like

488
00:25:26,920 --> 00:25:29,240
Speaker 1: added a whole bunch more stuff to it, it wouldn't

489
00:25:29,240 --> 00:25:32,159
Speaker 1: actually get much bigger. It would just get denser. Why

490
00:25:32,520 --> 00:25:34,879
Speaker 1: because of gravity, right, it would just keep compressing it.

491
00:25:34,920 --> 00:25:37,399
Speaker 1: Because the stuff inside the Earth does get compressed, it

492
00:25:37,440 --> 00:25:40,240
Speaker 1: still resists gravity. It's not yet collapsing to a black hole.

493
00:25:40,480 --> 00:25:43,359
Speaker 1: Eventually that would happen if you added enough mass. But

494
00:25:43,440 --> 00:25:45,920
Speaker 1: as you keep adding mass to the Earth, for example,

495
00:25:45,920 --> 00:25:49,000
Speaker 1: it gets denser and denser and denser, And so in

496
00:25:49,040 --> 00:25:51,280
Speaker 1: the Solar System, the Earth is sort of at the

497
00:25:51,359 --> 00:25:53,760
Speaker 1: extreme of all of these balancing factors.

498
00:25:53,960 --> 00:25:56,680
Speaker 3: Oh man, it's nice that for once, Earth is special

499
00:25:56,720 --> 00:25:57,359
Speaker 3: in some way.

500
00:25:57,680 --> 00:25:57,919
Speaker 2: You know.

501
00:25:58,680 --> 00:26:01,320
Speaker 3: Wait, once we got decenter from the universe, you know,

502
00:26:01,359 --> 00:26:02,719
Speaker 3: that was a little bit of a bummer. But this

503
00:26:02,760 --> 00:26:03,760
Speaker 3: is making me feel good.

504
00:26:03,880 --> 00:26:07,880
Speaker 1: So Jupiter's density is just above that of water. Mercury

505
00:26:08,000 --> 00:26:10,919
Speaker 1: is like five point four times that, and Earth just

506
00:26:11,080 --> 00:26:14,800
Speaker 1: tops out mercury at five point five. Venus is close

507
00:26:14,880 --> 00:26:17,920
Speaker 1: at five point two. But Earth is definitely king of

508
00:26:17,960 --> 00:26:20,760
Speaker 1: the Solar System in terms of density. Yay, we are

509
00:26:20,800 --> 00:26:22,000
Speaker 1: the densesto.

510
00:26:22,440 --> 00:26:26,320
Speaker 3: Hey man, I'll take what I can get. Oh wait,

511
00:26:26,359 --> 00:26:28,680
Speaker 3: does that mean we've quit? Like we're not pushing back

512
00:26:28,680 --> 00:26:29,560
Speaker 3: as much anymore?

513
00:26:30,160 --> 00:26:30,560
Speaker 2: Is this? No?

514
00:26:30,680 --> 00:26:32,240
Speaker 3: Never mind, don't think too hard about it. It's not

515
00:26:32,240 --> 00:26:35,360
Speaker 3: a sign of failure. It's a sign of success exactly.

516
00:26:35,480 --> 00:26:38,199
Speaker 1: But planets are also not the densest things in the

517
00:26:38,240 --> 00:26:42,600
Speaker 1: Solar System. So stars which are actively fusing, they have

518
00:26:42,680 --> 00:26:45,160
Speaker 1: a lot of radiation pressure keeps them from getting very dense.

519
00:26:45,400 --> 00:26:48,200
Speaker 1: Planets you can make them denser than stars, but if

520
00:26:48,200 --> 00:26:49,879
Speaker 1: you make them too dense, they start to fuse.

521
00:26:50,119 --> 00:26:51,919
Speaker 3: And then once we fuse, we start pushing back out

522
00:26:51,960 --> 00:26:54,399
Speaker 3: again and density goes down again. Yeah, exactly, I've been

523
00:26:54,400 --> 00:26:55,400
Speaker 3: listening exactly.

524
00:26:55,800 --> 00:26:58,080
Speaker 1: But you could also play another game and say, well,

525
00:26:58,119 --> 00:27:00,880
Speaker 1: I'm just gonna wait for fusion to run out. Right,

526
00:27:00,960 --> 00:27:03,639
Speaker 1: what happens when fusion burns itself out. We've been talking

527
00:27:03,640 --> 00:27:07,960
Speaker 1: about how stars have a certain lifetime, and eventually fusion

528
00:27:08,040 --> 00:27:10,880
Speaker 1: runs out because it relies on fuel in certain conditions.

529
00:27:10,960 --> 00:27:13,160
Speaker 3: And I'm going to guess this is where our brilliant

530
00:27:13,200 --> 00:27:16,760
Speaker 3: listeners come in and is the next stage of neutron star?

531
00:27:17,440 --> 00:27:18,120
Speaker 1: Not yet?

532
00:27:18,119 --> 00:27:19,639
Speaker 3: Oh man, almost right.

533
00:27:19,640 --> 00:27:22,000
Speaker 1: We're not quite there yet. But think about the life

534
00:27:22,040 --> 00:27:24,520
Speaker 1: cycle of our star. What's going to happen. Well, we

535
00:27:24,600 --> 00:27:27,120
Speaker 1: have a fairly low mass star. It's going to burn

536
00:27:27,160 --> 00:27:30,679
Speaker 1: and burn and burn, and it's burning mostly hydrogen and

537
00:27:30,760 --> 00:27:33,960
Speaker 1: it's accumulating helium at its core, but it's not hot

538
00:27:34,080 --> 00:27:36,520
Speaker 1: enough to burn that helium, so that helium is just

539
00:27:36,560 --> 00:27:38,760
Speaker 1: sort of like ash. It gets in the way of fusion,

540
00:27:39,240 --> 00:27:42,640
Speaker 1: and so as the core builds up helium, the fusion

541
00:27:42,640 --> 00:27:45,200
Speaker 1: gets pushed to the outside, so we have fusion instead

542
00:27:45,200 --> 00:27:46,800
Speaker 1: of at the core, now you have it in the

543
00:27:46,800 --> 00:27:48,639
Speaker 1: middle and then in the outer layers. And so the

544
00:27:48,680 --> 00:27:51,600
Speaker 1: star blows up to become a red giant as the

545
00:27:51,640 --> 00:27:53,640
Speaker 1: fusion starts happening in its core. And this is why

546
00:27:53,640 --> 00:27:56,040
Speaker 1: people say the star is going to absorb the Earth,

547
00:27:56,080 --> 00:27:58,200
Speaker 1: because the radius of our sun is going to get

548
00:27:58,320 --> 00:28:01,840
Speaker 1: enormous as the helium core heats up. But eventually, for

549
00:28:01,880 --> 00:28:04,760
Speaker 1: a brief moment, the star will go across that threshold

550
00:28:04,840 --> 00:28:07,439
Speaker 1: be able to burn helium for like literally a minute,

551
00:28:07,880 --> 00:28:10,560
Speaker 1: and there'll be a helium flash where the helium fuses,

552
00:28:10,960 --> 00:28:13,440
Speaker 1: and that'll blow out the star and you'll be left

553
00:28:13,480 --> 00:28:16,119
Speaker 1: with a nebula, like you know, the outer edges of

554
00:28:16,160 --> 00:28:18,480
Speaker 1: the star blown out, and that the core will be

555
00:28:18,520 --> 00:28:21,600
Speaker 1: a remnant, which for our star is a white dwarf,

556
00:28:22,040 --> 00:28:25,320
Speaker 1: and a white dwarf is just that core of unburnable stuff,

557
00:28:25,440 --> 00:28:29,200
Speaker 1: leftover stuff from fusion where the star was not massive

558
00:28:29,280 --> 00:28:30,800
Speaker 1: enough to fuse it. So it's just sort of like

559
00:28:31,000 --> 00:28:35,199
Speaker 1: unfusible fuel left over, but very hot and very dense.

560
00:28:35,400 --> 00:28:36,679
Speaker 1: And that's a white dwarf.

561
00:28:36,840 --> 00:28:40,280
Speaker 3: Oh my god. Okay, So I imagine that that one

562
00:28:40,320 --> 00:28:42,440
Speaker 3: minute period that you were talking about where the helium

563
00:28:42,560 --> 00:28:44,680
Speaker 3: is burning is going to differ depending on like what

564
00:28:44,800 --> 00:28:47,239
Speaker 3: kind of star you're talking about. So but still, I

565
00:28:47,240 --> 00:28:49,840
Speaker 3: imagine this a very narrow amount of time during which

566
00:28:49,840 --> 00:28:53,440
Speaker 3: you could catch this happening. But that sounds amazing. Have

567
00:28:53,560 --> 00:28:56,080
Speaker 3: we caught this like on any of our telescopes.

568
00:28:56,440 --> 00:28:59,720
Speaker 1: No, because unfortunately it's mostly internal. The helium flash is

569
00:28:59,720 --> 00:29:03,160
Speaker 1: absorbed by the star, And we've looked for these things

570
00:29:03,240 --> 00:29:06,120
Speaker 1: on other stars, but we've never actually seen them because

571
00:29:06,160 --> 00:29:09,920
Speaker 1: again it's mostly internal and absorbed. People are trying to

572
00:29:09,960 --> 00:29:13,640
Speaker 1: study it by doing astro seismology, looking at like periodic

573
00:29:13,720 --> 00:29:16,280
Speaker 1: changes in a star's brightness to see if maybe something

574
00:29:16,360 --> 00:29:20,200
Speaker 1: is happening internally, or looking for other kinds of indirect evidence,

575
00:29:20,200 --> 00:29:23,320
Speaker 1: but we've never directly seen a helium flash. So currently

576
00:29:23,400 --> 00:29:24,720
Speaker 1: it's still theoretical.

577
00:29:24,960 --> 00:29:27,200
Speaker 3: Okay, but it's definitely awesome.

578
00:29:27,400 --> 00:29:30,240
Speaker 1: Yeah, it's definitely awesome. And so what's left over and

579
00:29:30,280 --> 00:29:32,520
Speaker 1: the white dwarf depends on how big the star was.

580
00:29:32,800 --> 00:29:35,560
Speaker 1: The bigger the star, the hotter the core, the more

581
00:29:35,600 --> 00:29:38,560
Speaker 1: elements you confuse, and the biggest star confuse all the

582
00:29:38,600 --> 00:29:41,640
Speaker 1: way up to iron. Smaller stars like ours can only

583
00:29:41,680 --> 00:29:44,560
Speaker 1: form things like carbon and oxygen. But that's what the

584
00:29:44,600 --> 00:29:46,479
Speaker 1: white dwarf is going to be made out of. And

585
00:29:46,520 --> 00:29:49,440
Speaker 1: these things are incredibly dense. They can have a mass

586
00:29:49,480 --> 00:29:52,040
Speaker 1: of up to the mass of our Sun. Our sun

587
00:29:52,080 --> 00:29:53,960
Speaker 1: won't leave a white dwarf the mass of the Sun

588
00:29:54,040 --> 00:29:56,560
Speaker 1: because some of the mass is blown out, but bigger

589
00:29:56,600 --> 00:29:58,880
Speaker 1: stars up to like eight times the mass of our

590
00:29:58,920 --> 00:30:01,880
Speaker 1: Sun can leave a white dwarf. And the core there

591
00:30:01,960 --> 00:30:03,640
Speaker 1: is like the mass of our sun.

592
00:30:03,840 --> 00:30:04,040
Speaker 2: Wow.

593
00:30:04,240 --> 00:30:06,680
Speaker 1: And the radius is very small, it's only like ten

594
00:30:06,760 --> 00:30:11,520
Speaker 1: thousand kilometers. And so these things are incredibly dense. Density

595
00:30:11,520 --> 00:30:15,200
Speaker 1: of like ten to the ten kilograms per cubic meters

596
00:30:15,560 --> 00:30:18,440
Speaker 1: earlier we were talking about like thousands of kilograms per

597
00:30:18,480 --> 00:30:23,040
Speaker 1: cubic meters. This is like ten billion kilograms per cubic meters.

598
00:30:23,080 --> 00:30:24,520
Speaker 1: Really incredibly dense.

599
00:30:24,680 --> 00:30:27,320
Speaker 3: Holy cow. Okay. And the reason even though it's so dense,

600
00:30:27,400 --> 00:30:29,760
Speaker 3: it's not fusing because it's already burned up all of

601
00:30:29,760 --> 00:30:32,280
Speaker 3: its fusion fuel, so fusion can't happen anymore.

602
00:30:32,400 --> 00:30:35,040
Speaker 1: Yeah, exactly, it's not dense enough to have any more fusion.

603
00:30:35,320 --> 00:30:37,400
Speaker 1: But if something comes along and leaks a little bit

604
00:30:37,440 --> 00:30:39,480
Speaker 1: of mass to the white dwarf so it can compress

605
00:30:39,480 --> 00:30:43,080
Speaker 1: further and overcome the quantum forces. Then does suddenly trigger

606
00:30:43,120 --> 00:30:45,400
Speaker 1: fusion in the whole star and blow the thing up

607
00:30:45,440 --> 00:30:47,800
Speaker 1: as a type one A supernova. That's how type one

608
00:30:47,840 --> 00:30:49,040
Speaker 1: A supernovas are formed.

609
00:30:49,200 --> 00:30:50,880
Speaker 2: What that sauce?

610
00:30:51,560 --> 00:30:53,800
Speaker 3: Oh, I kind of wish I could see this stuff.

611
00:30:54,760 --> 00:30:57,120
Speaker 3: I mean, i'd be dead, I know, but wow, Well we.

612
00:30:57,040 --> 00:30:59,480
Speaker 1: Can see them across the galaxy, which is why they're

613
00:30:59,480 --> 00:31:02,280
Speaker 1: so power for telling us about the expansion of the universe.

614
00:31:02,720 --> 00:31:04,560
Speaker 1: But the reason that their wife d warf is stable.

615
00:31:04,600 --> 00:31:07,000
Speaker 1: Like you might ask, what's keeping this thing from collapsing

616
00:31:07,000 --> 00:31:10,000
Speaker 1: into a black hole anyway? And it's not like the

617
00:31:10,040 --> 00:31:13,640
Speaker 1: structural integrity of iron or carbon the way the Earth is,

618
00:31:13,720 --> 00:31:16,320
Speaker 1: And it's not fusion the way a star is. It's

619
00:31:16,320 --> 00:31:20,280
Speaker 1: something else called electron degeneracy pressure. Instead of thinking about

620
00:31:20,320 --> 00:31:23,239
Speaker 1: this object as made of individual atoms, think about it

621
00:31:23,280 --> 00:31:25,480
Speaker 1: like a metal. What happens in a metal is the

622
00:31:25,480 --> 00:31:27,800
Speaker 1: electrons all sort of flow around, and you have like

623
00:31:27,800 --> 00:31:32,160
Speaker 1: electron energy levels across the metal, like conduction band, valence band,

624
00:31:32,240 --> 00:31:34,720
Speaker 1: all that kind of stuff. Well, what's happening here is

625
00:31:34,760 --> 00:31:37,800
Speaker 1: that the electrons, because they're fermions, they're the kind of

626
00:31:37,800 --> 00:31:39,440
Speaker 1: particle where you can't have two of them in the

627
00:31:39,480 --> 00:31:43,480
Speaker 1: same state. They can't collapse to low energy levels because

628
00:31:43,520 --> 00:31:46,200
Speaker 1: those are occupied, and so the electrons are forced to

629
00:31:46,280 --> 00:31:49,400
Speaker 1: stay in higher energy levels because they can't go down

630
00:31:49,400 --> 00:31:52,480
Speaker 1: to those occupied levels, and that means they have higher energy,

631
00:31:52,480 --> 00:31:55,640
Speaker 1: which means they're flying around, bouncing against stuff, and that's

632
00:31:55,680 --> 00:31:59,400
Speaker 1: where electron degeneracy pressure comes from. People often write and

633
00:31:59,440 --> 00:32:02,000
Speaker 1: ask me, like, what is the poly exclusion principle? What

634
00:32:02,080 --> 00:32:04,440
Speaker 1: force is acting on it? It's not one of the

635
00:32:04,520 --> 00:32:07,520
Speaker 1: quantum forces. It's not electricity, magnetism, it's not the weak force,

636
00:32:07,600 --> 00:32:10,240
Speaker 1: not the strong force. What force are we talking about here?

637
00:32:10,440 --> 00:32:13,280
Speaker 1: It's not any individual force. It's this quantum rule that

638
00:32:13,360 --> 00:32:16,719
Speaker 1: prevents electrons from going to lower energy. So they have

639
00:32:16,760 --> 00:32:19,200
Speaker 1: a higher energy, so they bounce off the stuff and

640
00:32:19,240 --> 00:32:20,120
Speaker 1: apply pressure.

641
00:32:20,320 --> 00:32:23,840
Speaker 3: Huh okay, and that's what keeps the white dwarf white

642
00:32:23,880 --> 00:32:24,400
Speaker 3: dwarf fyet.

643
00:32:24,520 --> 00:32:27,560
Speaker 1: Yeah, exactly. That's the thing that prevents gravity from collapsing

644
00:32:27,680 --> 00:32:30,240
Speaker 1: into a black hole. Those electrons do not want to

645
00:32:30,280 --> 00:32:32,960
Speaker 1: go down into that lower energy, so they keep having

646
00:32:33,040 --> 00:32:34,920
Speaker 1: high energy and they push back in the same way

647
00:32:34,960 --> 00:32:38,840
Speaker 1: that radiation pressure keeps a star from collapsing, electron degeneracy

648
00:32:38,920 --> 00:32:41,320
Speaker 1: pressure keeps a white dwarf from collapsing.

649
00:32:41,480 --> 00:32:43,160
Speaker 3: All Right, So I'm on the edge of my seat

650
00:32:43,160 --> 00:32:44,680
Speaker 3: now because i know that at some point we have

651
00:32:44,720 --> 00:32:46,640
Speaker 3: to get to neutron stars, and I'm guessing we're going

652
00:32:46,680 --> 00:32:50,040
Speaker 3: to get there through white dwarfs, and so maybe something

653
00:32:50,080 --> 00:32:54,040
Speaker 3: goes wrong with electron degeneracy pressure. But let's go ahead

654
00:32:54,040 --> 00:33:10,840
Speaker 3: and take a break and find out when we get back,

655
00:33:15,800 --> 00:33:18,120
Speaker 3: all right, Daniel. At the beginning of this episode, the

656
00:33:18,200 --> 00:33:21,920
Speaker 3: Extraordinaries pointed out that neutron stars are very dense. And

657
00:33:21,960 --> 00:33:24,360
Speaker 3: we've explained how you get to white dwarves and how

658
00:33:24,440 --> 00:33:28,840
Speaker 3: electron degeneracy pressure keeps the white dwarf from collapsing even

659
00:33:28,880 --> 00:33:31,520
Speaker 3: further into a black hole. How do we get to

660
00:33:31,560 --> 00:33:32,400
Speaker 3: neutron stars.

661
00:33:32,720 --> 00:33:34,480
Speaker 1: Yeah, so to get to neutron stars, you have to

662
00:33:34,520 --> 00:33:37,960
Speaker 1: overcome this electron degenescy pressure, which means either adding more

663
00:33:38,000 --> 00:33:41,200
Speaker 1: mass to a white dwarf or just having more mass

664
00:33:41,240 --> 00:33:44,520
Speaker 1: in the star. Initially, this leads to a type two supernova,

665
00:33:44,920 --> 00:33:47,720
Speaker 1: when that last moment of fusion in our star would

666
00:33:47,720 --> 00:33:50,000
Speaker 1: have been a helium flash, but in a bigger star,

667
00:33:50,080 --> 00:33:52,960
Speaker 1: that's a supernova, and it blows out the outer edges

668
00:33:53,160 --> 00:33:56,000
Speaker 1: much more dramatically, and instead of getting a white dwarf

669
00:33:56,040 --> 00:33:58,400
Speaker 1: at the core, you get a neutron star. And what

670
00:33:58,480 --> 00:34:01,760
Speaker 1: happens here is that you've overcome the electron degenerously pressure

671
00:34:01,800 --> 00:34:05,480
Speaker 1: just by having more mass, and you squeeze those electrons

672
00:34:05,520 --> 00:34:10,160
Speaker 1: into the protons and made neutrons. This is inverse beta decay.

673
00:34:10,400 --> 00:34:13,080
Speaker 1: Beta decays when a neutron decays into an electron and

674
00:34:13,120 --> 00:34:16,359
Speaker 1: a proton. This is like you squeeze the electron back

675
00:34:16,440 --> 00:34:19,759
Speaker 1: into the proton and you form a neutron. And so

676
00:34:19,800 --> 00:34:23,280
Speaker 1: that's what a neutron star is. When you've said screw you, electrons,

677
00:34:23,320 --> 00:34:24,800
Speaker 1: I'm pushing you into those states.

678
00:34:24,880 --> 00:34:27,200
Speaker 3: Holy cow, eat it all right, that's intense. So are

679
00:34:27,200 --> 00:34:30,960
Speaker 3: there any electrons or protons left or they're all smooshed

680
00:34:31,160 --> 00:34:33,719
Speaker 3: into neutrons. There's probably an equal number of them.

681
00:34:33,880 --> 00:34:36,239
Speaker 1: Neutron star is mostly made of neutrons. There are going

682
00:34:36,280 --> 00:34:38,759
Speaker 1: to be some protons in there as well, and a

683
00:34:38,760 --> 00:34:41,800
Speaker 1: few electrons. Especially at the edge. We don't know exactly

684
00:34:41,840 --> 00:34:43,960
Speaker 1: what's happening, and then at the core we really don't

685
00:34:44,040 --> 00:34:48,160
Speaker 1: understand but these things are incredibly dense. They're still like

686
00:34:48,360 --> 00:34:50,520
Speaker 1: one to three times the mass of the Sun, but

687
00:34:50,520 --> 00:34:53,480
Speaker 1: the radius is only ten to fifteen kilometers.

688
00:34:53,640 --> 00:34:53,839
Speaker 3: Wow.

689
00:34:54,000 --> 00:34:56,759
Speaker 1: The white dwarfs the radius was like ten thousand kilometers.

690
00:34:56,960 --> 00:35:00,440
Speaker 1: This thing is a radius of ten kilometers the size

691
00:35:00,440 --> 00:35:04,080
Speaker 1: of Los Angeles, right, and its density is ten to

692
00:35:04,120 --> 00:35:08,480
Speaker 1: the seventeen kilograms per cubic meters, so like ten million

693
00:35:08,600 --> 00:35:11,080
Speaker 1: times the density of the white dwarf.

694
00:35:11,280 --> 00:35:14,880
Speaker 3: Wow. Okay, but still somehow that's not enough to become

695
00:35:14,920 --> 00:35:15,600
Speaker 3: a black hole.

696
00:35:15,760 --> 00:35:18,000
Speaker 1: That's still not enough to become a black hole because

697
00:35:18,040 --> 00:35:21,719
Speaker 1: at the core quantum mechanics is still pushing back, and

698
00:35:21,800 --> 00:35:24,960
Speaker 1: these neutrons are neutral electromagnetically, but they still have the

699
00:35:25,000 --> 00:35:27,640
Speaker 1: strong force. And when you get at the core, even

700
00:35:27,640 --> 00:35:30,880
Speaker 1: the neutrons themselves start to merge, and you don't just

701
00:35:30,880 --> 00:35:33,840
Speaker 1: get individual neutrons to get pushed into something called like

702
00:35:33,880 --> 00:35:38,479
Speaker 1: a cork gluon plasma or these other hypothetical states of matter,

703
00:35:38,520 --> 00:35:40,200
Speaker 1: for example nuclear pasta.

704
00:35:40,400 --> 00:35:43,200
Speaker 3: Oh, I've been waiting all episode for us to get

705
00:35:43,239 --> 00:35:47,640
Speaker 3: to the nuclear pasta. Okay, tell me about the Noki phase.

706
00:35:48,320 --> 00:35:49,680
Speaker 3: How do you pronounce that?

707
00:35:51,480 --> 00:35:53,560
Speaker 1: So if you have a few protons left over and

708
00:35:53,600 --> 00:35:55,800
Speaker 1: you do the calculations of what happens when you compress

709
00:35:55,920 --> 00:35:59,600
Speaker 1: neutrons really really far. You get these weird blobs. So

710
00:35:59,680 --> 00:36:03,720
Speaker 1: this called the Niolki phase. We have these semi spherical blobs,

711
00:36:03,760 --> 00:36:06,319
Speaker 1: and this is just what emerges from the calculations. You like,

712
00:36:06,480 --> 00:36:10,600
Speaker 1: run your simulations and you get these blobs. But sometimes

713
00:36:10,760 --> 00:36:13,120
Speaker 1: instead you get the spaghetti phase where you get like

714
00:36:13,239 --> 00:36:16,320
Speaker 1: long rods of neutrons form, or they have a phase

715
00:36:16,400 --> 00:36:19,440
Speaker 1: with the like sheets of neutrons they call the Lasagna

716
00:36:19,480 --> 00:36:23,480
Speaker 1: phase because of course, or another phase they call the

717
00:36:23,520 --> 00:36:26,880
Speaker 1: anti spaghetti phase where you roll those sheets up back

718
00:36:26,960 --> 00:36:27,720
Speaker 1: into rods.

719
00:36:27,719 --> 00:36:29,480
Speaker 3: I feel like they're losing the plot there.

720
00:36:32,000 --> 00:36:33,840
Speaker 1: So we don't know if this is what's actually happening

721
00:36:33,840 --> 00:36:37,640
Speaker 1: inside the neutron star. But here remember neutrons are also fermions,

722
00:36:38,000 --> 00:36:41,080
Speaker 1: so the polyexclusion principle applies to them as well. So

723
00:36:41,239 --> 00:36:44,359
Speaker 1: even though they're neutral, they resist collapse because they don't

724
00:36:44,400 --> 00:36:46,560
Speaker 1: want to be in the same state either. And so

725
00:36:46,600 --> 00:36:50,200
Speaker 1: that's quantum mechanics, like last ditch effort to avoid being

726
00:36:50,200 --> 00:36:52,319
Speaker 1: turned into a black hole. But if you take a

727
00:36:52,320 --> 00:36:55,000
Speaker 1: neutron star and you add more mass to it or

728
00:36:55,000 --> 00:36:58,799
Speaker 1: equivalently if you started with a much bigger star, more

729
00:36:58,840 --> 00:37:01,120
Speaker 1: than forty times the mass of our Sun. Then when

730
00:37:01,160 --> 00:37:03,200
Speaker 1: you have that super nova and then the collapse, you

731
00:37:03,239 --> 00:37:05,600
Speaker 1: don't get a neutron star. You get a black hole.

732
00:37:06,200 --> 00:37:08,960
Speaker 3: And I'm just trying to imagine, like add more mass

733
00:37:08,960 --> 00:37:12,600
Speaker 3: to it. Might mean that like dust from nearby gets

734
00:37:12,600 --> 00:37:15,640
Speaker 3: sucked in, or like a comet that's passing by gets

735
00:37:15,640 --> 00:37:17,640
Speaker 3: sucked in, and that adds a lot more mass. Is

736
00:37:17,680 --> 00:37:18,720
Speaker 3: that how you get the mass?

737
00:37:18,880 --> 00:37:20,719
Speaker 1: Maybe, but that's probably not going to be enough. I

738
00:37:20,719 --> 00:37:23,840
Speaker 1: think more typically you'll have a binary star system and

739
00:37:23,920 --> 00:37:26,319
Speaker 1: it'll absorb one of its neighbors. And so you see

740
00:37:26,320 --> 00:37:27,960
Speaker 1: these systems where like one of them is a white

741
00:37:28,000 --> 00:37:29,799
Speaker 1: dwarf for a neutron star, and the other one is

742
00:37:29,800 --> 00:37:32,920
Speaker 1: a still burning, puffy star and its partner is like

743
00:37:33,040 --> 00:37:35,960
Speaker 1: slurping on it. You see there's like tendrils of gas

744
00:37:36,280 --> 00:37:38,520
Speaker 1: space exactly.

745
00:37:38,680 --> 00:37:39,840
Speaker 2: Yea, we get.

746
00:37:41,960 --> 00:37:45,719
Speaker 1: Job. But the question of this episode is can you

747
00:37:45,800 --> 00:37:48,440
Speaker 1: go beyond a neutron star? Is there something denser than

748
00:37:48,440 --> 00:37:51,640
Speaker 1: a neutron star which can still resist the force of gravity?

749
00:37:51,800 --> 00:37:53,040
Speaker 3: And what's the answer, Daniel.

750
00:37:54,600 --> 00:37:57,359
Speaker 1: So we're trapped between a neutron star and a black hole,

751
00:37:57,400 --> 00:37:58,920
Speaker 1: So let's put some numbers on it to make a

752
00:37:58,960 --> 00:38:03,640
Speaker 1: concrete and counterintuitively, also the density of black holes is confusing.

753
00:38:04,000 --> 00:38:07,160
Speaker 1: As black holes get more massive, their radius goes up,

754
00:38:07,440 --> 00:38:10,160
Speaker 1: and so they're also not super dense. For example, a

755
00:38:10,200 --> 00:38:12,440
Speaker 1: black hole the size of our solar system has the

756
00:38:12,480 --> 00:38:15,719
Speaker 1: density of about water, but smaller black holes have a

757
00:38:15,719 --> 00:38:20,240
Speaker 1: smaller radius, they're incredibly dense. So let's imagine our neutron

758
00:38:20,320 --> 00:38:22,879
Speaker 1: star scenario. We have a mass of like two times

759
00:38:22,960 --> 00:38:25,400
Speaker 1: the mass of the Sun, a radius of ten kilometers.

760
00:38:25,680 --> 00:38:28,719
Speaker 1: That's a density of like ten to the eighteen kilograms

761
00:38:28,760 --> 00:38:31,960
Speaker 1: per meter's cube. If you collapse it to a black hole,

762
00:38:31,960 --> 00:38:35,000
Speaker 1: would require squishing that ten kilometer radius star down to

763
00:38:35,040 --> 00:38:38,120
Speaker 1: about six kilometers, and that would make a density of

764
00:38:38,200 --> 00:38:41,399
Speaker 1: five times the neutron star. So we're wondering if there's

765
00:38:41,400 --> 00:38:44,040
Speaker 1: a place between the density of that neutron star and

766
00:38:44,160 --> 00:38:47,120
Speaker 1: the five times density of a black hole where something

767
00:38:47,200 --> 00:38:49,680
Speaker 1: can survive and not collapse gravitationally.

768
00:38:49,760 --> 00:38:51,359
Speaker 3: So, just to make sure that I'm understanding, so you

769
00:38:51,400 --> 00:38:54,400
Speaker 3: said that some black holes could have the density of water,

770
00:38:54,480 --> 00:38:57,080
Speaker 3: and we talked earlier about how our sun has the

771
00:38:57,120 --> 00:39:00,839
Speaker 3: density of water. So does that mean that there are

772
00:39:00,880 --> 00:39:04,440
Speaker 3: blue giants out there that are denser than some black holes.

773
00:39:04,719 --> 00:39:06,640
Speaker 1: There are blue giants out there that are denser than

774
00:39:06,680 --> 00:39:09,840
Speaker 1: some black holes. Absolutely, because a black hole that's super

775
00:39:09,840 --> 00:39:12,920
Speaker 1: big is not very dense. And here we're defining density

776
00:39:13,000 --> 00:39:15,960
Speaker 1: as the massive thing divided by the event horizon. We

777
00:39:16,000 --> 00:39:18,640
Speaker 1: don't know inside the black hole how that mass is distributed,

778
00:39:18,640 --> 00:39:21,640
Speaker 1: if there's a singularity of infinite density, if it's smoothly distributed,

779
00:39:21,640 --> 00:39:24,120
Speaker 1: if there's weird quantum stuff happening, if there's a black

780
00:39:24,160 --> 00:39:27,120
Speaker 1: hole squid pasta. We have no idea, but we're just

781
00:39:27,200 --> 00:39:29,759
Speaker 1: sort of assigning the average density of the black hole.

782
00:39:29,880 --> 00:39:32,319
Speaker 3: Okay, all right, So we've got a range of densities,

783
00:39:32,880 --> 00:39:35,160
Speaker 3: and we're trying to figure out if there's anything between

784
00:39:35,880 --> 00:39:39,360
Speaker 3: a neutron star and the least dense black.

785
00:39:39,120 --> 00:39:41,479
Speaker 1: Hole, well, between a neutron star and the black hole

786
00:39:41,520 --> 00:39:44,399
Speaker 1: it would eventually collapse into, which would be quite dense. Okay,

787
00:39:44,440 --> 00:39:46,719
Speaker 1: And I chose a neutron star because the black hole

788
00:39:46,760 --> 00:39:49,600
Speaker 1: it would collapse into would be quite small six kilometers

789
00:39:49,600 --> 00:39:52,839
Speaker 1: and very very dense. And so we're wondering if there's

790
00:39:52,880 --> 00:39:56,360
Speaker 1: a possibility in between. And so there's an Australian physicist

791
00:39:56,440 --> 00:39:59,320
Speaker 1: Hans Bookdall, who thought about this stuff several decades ago.

792
00:40:00,000 --> 00:40:02,560
Speaker 1: He came up with this really clever calculation and he

793
00:40:02,640 --> 00:40:06,200
Speaker 1: proved this limit that said that nothing can be smaller

794
00:40:06,239 --> 00:40:09,640
Speaker 1: than twelve percent larger than the radius of a black hole.

795
00:40:10,040 --> 00:40:12,360
Speaker 1: So if you have a certain mass, you can calculate

796
00:40:12,440 --> 00:40:14,600
Speaker 1: what the black hole radius would be. For our case,

797
00:40:14,640 --> 00:40:16,720
Speaker 1: for two times the mass of the Sun, our neutron

798
00:40:16,760 --> 00:40:19,680
Speaker 1: star with a radius ten kilometers, the black hole radius

799
00:40:19,719 --> 00:40:23,200
Speaker 1: is six kilometers, and he says that nothing can survive

800
00:40:23,719 --> 00:40:27,480
Speaker 1: less than seven kilometers without collapsing into a black hole.

801
00:40:27,680 --> 00:40:30,320
Speaker 1: But then in principle it is possible. So he was

802
00:40:30,360 --> 00:40:32,720
Speaker 1: thinking about in terms of the radius of a black hole,

803
00:40:32,920 --> 00:40:35,920
Speaker 1: which is a short siled radius, and for that given mass,

804
00:40:36,160 --> 00:40:39,080
Speaker 1: he said that nothing can be smaller than a radius

805
00:40:39,120 --> 00:40:42,120
Speaker 1: of nine eighths of the sort chiled radius, so like

806
00:40:42,400 --> 00:40:45,200
Speaker 1: twelve percent bigger than the short siled radius. If you

807
00:40:45,239 --> 00:40:47,480
Speaker 1: get smaller than that, then you have to collapse into

808
00:40:47,480 --> 00:40:50,200
Speaker 1: a black hole. But theoretically it's possible to have an

809
00:40:50,239 --> 00:40:53,640
Speaker 1: object that's like nine eighths the radius of the short

810
00:40:53,680 --> 00:40:56,359
Speaker 1: filed radius, which would not yet be a black hole.

811
00:40:56,760 --> 00:41:00,359
Speaker 3: Okay, but like, my hat is smaller than that, and

812
00:41:00,440 --> 00:41:05,000
Speaker 3: so by like, by nothing do you mean know celestial bodies?

813
00:41:05,640 --> 00:41:07,799
Speaker 1: Well, your hat has a tiny mass, and so the

814
00:41:07,800 --> 00:41:10,520
Speaker 1: swart Child radius for your hat is very, very small.

815
00:41:10,560 --> 00:41:13,480
Speaker 1: And book Doll is saying that your hat, in principle

816
00:41:13,800 --> 00:41:17,240
Speaker 1: could resist becoming a black hole by staying at nine

817
00:41:17,400 --> 00:41:20,240
Speaker 1: eighths of the swart Child radius of your hat.

818
00:41:20,480 --> 00:41:21,600
Speaker 3: Oh, okay, all right.

819
00:41:21,680 --> 00:41:24,239
Speaker 1: And so in the case of our neutron star, it's

820
00:41:24,400 --> 00:41:27,359
Speaker 1: short Chiled radius is six kilometers and its book Doll

821
00:41:27,520 --> 00:41:31,120
Speaker 1: radius is about seven kilometers. So book Doll did this

822
00:41:31,160 --> 00:41:33,840
Speaker 1: cool calculation. And the way he got this number is

823
00:41:33,840 --> 00:41:36,040
Speaker 1: he said, well, let me make some assumptions. Let me

824
00:41:36,080 --> 00:41:39,680
Speaker 1: assume that pressure in the object is finite, and that

825
00:41:39,719 --> 00:41:43,880
Speaker 1: density increases monotonically from the inside to the outside. So

826
00:41:43,920 --> 00:41:46,520
Speaker 1: you have this sort of simplified object. It's a perfect

827
00:41:46,520 --> 00:41:50,040
Speaker 1: fluid with isotopic pressure. And in a Newtonian world, where

828
00:41:50,080 --> 00:41:52,920
Speaker 1: gravity is just like a force between two objects, there

829
00:41:53,000 --> 00:41:55,520
Speaker 1: is no limit here on the density of an object.

830
00:41:55,719 --> 00:42:01,000
Speaker 1: But in general relativity pressure contributes to gravity, so as

831
00:42:01,120 --> 00:42:04,520
Speaker 1: something gets denser, it has more pressure pushing out. Actually,

832
00:42:04,560 --> 00:42:09,480
Speaker 1: gravitates also increases the gravitational pull on the object, and

833
00:42:09,560 --> 00:42:13,720
Speaker 1: so Oakdahl discovered this limit where the pressure essentially becomes infinite.

834
00:42:14,040 --> 00:42:17,520
Speaker 1: So you can't have an object smaller than nine eighths

835
00:42:17,560 --> 00:42:20,640
Speaker 1: of their short stiled radius without that pressure blowing up

836
00:42:20,800 --> 00:42:23,640
Speaker 1: and becoming infinite. And therefore that thing would have to

837
00:42:23,680 --> 00:42:27,360
Speaker 1: collapse into a black hole. It couldn't survive under those conditions.

838
00:42:27,520 --> 00:42:33,279
Speaker 3: Okay, So Bechdahl did these calculations, and I'm guessing the

839
00:42:33,360 --> 00:42:37,399
Speaker 3: implication here is that he found that there is an

840
00:42:37,440 --> 00:42:41,440
Speaker 3: intermediate density that could exist between a black hole and

841
00:42:41,520 --> 00:42:45,319
Speaker 3: a neutron star exactly. But have we ever seen that.

842
00:42:45,840 --> 00:42:48,440
Speaker 1: We have not ever seen that, and this remains theoretical.

843
00:42:48,719 --> 00:42:51,560
Speaker 1: It's fascinating to understand that there is a limit to

844
00:42:51,600 --> 00:42:54,640
Speaker 1: the density. There is a maximum possible density you can

845
00:42:54,680 --> 00:42:57,520
Speaker 1: achieve before you get to a black hole. Neutron stars

846
00:42:57,560 --> 00:43:00,320
Speaker 1: do not achieve that density, And in order to achieve

847
00:43:00,360 --> 00:43:03,440
Speaker 1: that density, you'd need some kind of force which is

848
00:43:03,480 --> 00:43:08,200
Speaker 1: capable of resisting gravity more powerfully than neutron degenerousy pressure.

849
00:43:08,200 --> 00:43:10,480
Speaker 1: We don't know what that is, but in theory, if

850
00:43:10,520 --> 00:43:13,239
Speaker 1: it did exist in the universe, it could create what

851
00:43:13,280 --> 00:43:16,440
Speaker 1: they call a book doll star. This object with a

852
00:43:16,600 --> 00:43:19,560
Speaker 1: radius of nine eighths the short Child radius, not yet

853
00:43:19,600 --> 00:43:22,120
Speaker 1: a black hole, but something with a surface that you

854
00:43:22,160 --> 00:43:25,560
Speaker 1: could actually like land on that Kelly could swim in,

855
00:43:25,920 --> 00:43:27,759
Speaker 1: or you stand on the surface of and try to

856
00:43:27,760 --> 00:43:31,080
Speaker 1: lift her weights. But you know, we've seen black holes

857
00:43:31,120 --> 00:43:33,839
Speaker 1: in the universe, but we're not one hundred percent sure

858
00:43:34,040 --> 00:43:37,680
Speaker 1: they actually are black holes. Like we see objects out

859
00:43:37,719 --> 00:43:42,000
Speaker 1: there in the universe that are smaller and denser than

860
00:43:42,040 --> 00:43:44,919
Speaker 1: neutron stars can be, and so people say, oh, well,

861
00:43:44,960 --> 00:43:47,839
Speaker 1: therefore they must be black holes. And we see them

862
00:43:47,880 --> 00:43:50,520
Speaker 1: gravitating and we see things getting close to them, so

863
00:43:50,560 --> 00:43:52,920
Speaker 1: we can measure their radius. But our measurements are not

864
00:43:53,040 --> 00:43:56,000
Speaker 1: precise enough to actually tell us whether these things are

865
00:43:56,200 --> 00:44:00,640
Speaker 1: black holes or book doll stars because we can't see

866
00:44:00,640 --> 00:44:03,640
Speaker 1: the event horizon directly. We've observed the accretion disk, we've

867
00:44:03,640 --> 00:44:06,720
Speaker 1: seen the indirect effects, but that's a very small difference

868
00:44:06,719 --> 00:44:08,960
Speaker 1: between a book doll star and a black hole. So

869
00:44:09,000 --> 00:44:11,080
Speaker 1: in principle, some of the black holes we've seen could

870
00:44:11,120 --> 00:44:12,880
Speaker 1: actually be book do all stars.

871
00:44:13,120 --> 00:44:15,560
Speaker 3: Okay, so what do we need to know to differentiate

872
00:44:15,600 --> 00:44:16,160
Speaker 3: between those?

873
00:44:16,400 --> 00:44:19,040
Speaker 1: We need a more precise measurement of the radius of

874
00:44:19,080 --> 00:44:21,239
Speaker 1: these things. So, for example, the black hole of the

875
00:44:21,280 --> 00:44:23,440
Speaker 1: center of our galaxy, we don't know precisely what its

876
00:44:23,440 --> 00:44:26,560
Speaker 1: event horizon radius is. We've seen stuff go near it

877
00:44:26,600 --> 00:44:28,400
Speaker 1: and get sucked in, we've seen stuff go near it

878
00:44:28,440 --> 00:44:30,680
Speaker 1: and not get sucked in. That lets us measure it,

879
00:44:30,719 --> 00:44:33,680
Speaker 1: but it's not precise enough to distinguish between a black

880
00:44:33,719 --> 00:44:36,399
Speaker 1: hole or a book doll star. What we really need

881
00:44:36,480 --> 00:44:40,239
Speaker 1: is direct evidence of an event horizon. See something fall

882
00:44:40,280 --> 00:44:42,359
Speaker 1: in and red shift and act the way you would

883
00:44:42,360 --> 00:44:45,600
Speaker 1: expect something falling into a black hole to behave.

884
00:44:45,960 --> 00:44:49,640
Speaker 3: I volunteer, Zach, that's so nice.

885
00:44:49,440 --> 00:44:52,359
Speaker 1: Of you, really just for the sake of science. Or

886
00:44:52,520 --> 00:44:55,120
Speaker 1: the other direction you could go is you could think

887
00:44:55,200 --> 00:44:58,680
Speaker 1: hypothetically about what these objects might be. What is capable

888
00:44:58,719 --> 00:45:02,480
Speaker 1: of creating on our at that density or maintaining that

889
00:45:02,520 --> 00:45:05,880
Speaker 1: density and resisting the black holes collapse. And there's some

890
00:45:06,080 --> 00:45:11,719
Speaker 1: ideas out there fuzzballs or quark stars or weird hypothetical objects.

891
00:45:12,080 --> 00:45:13,759
Speaker 1: We have earlier episodes about them if you want to

892
00:45:13,800 --> 00:45:16,360
Speaker 1: learn more about them, and some of those have specific

893
00:45:16,400 --> 00:45:19,839
Speaker 1: predictions that you could look for that differ from just like, hey,

894
00:45:19,880 --> 00:45:22,560
Speaker 1: this is a very dense object that like short lifetimes

895
00:45:22,640 --> 00:45:25,839
Speaker 1: or other weird predictions. So you could try to make

896
00:45:25,880 --> 00:45:28,359
Speaker 1: predictions for what a theoretical object like this would look

897
00:45:28,400 --> 00:45:30,560
Speaker 1: like that's different from a black hole, and then look

898
00:45:30,600 --> 00:45:31,759
Speaker 1: for those signatures.

899
00:45:32,040 --> 00:45:34,640
Speaker 3: Wow. Okay, So where we are is we've definitely seen

900
00:45:34,719 --> 00:45:38,920
Speaker 3: neutron stars. We suspect there's this intermediate thing, and maybe

901
00:45:38,960 --> 00:45:41,719
Speaker 3: we've even been looking at the intermediate thing. He's being

902
00:45:41,719 --> 00:45:44,279
Speaker 3: the Bechdal stars. Every time I say it, I say

903
00:45:44,280 --> 00:45:45,600
Speaker 3: it a little different. That's fine.

904
00:45:46,360 --> 00:45:48,040
Speaker 1: He passed away ten years ago, so you don't have

905
00:45:48,040 --> 00:45:48,799
Speaker 1: to worry about it, all right.

906
00:45:48,800 --> 00:45:50,120
Speaker 3: He's not going to call me on it. That's good.

907
00:45:50,160 --> 00:45:53,200
Speaker 3: But so we might have already seen that kind of

908
00:45:53,239 --> 00:45:55,840
Speaker 3: star and black holes, and maybe one day we'll be

909
00:45:55,880 --> 00:45:58,160
Speaker 3: able to tell which is which, but at the moment

910
00:45:58,200 --> 00:45:58,560
Speaker 3: we can't.

911
00:45:58,920 --> 00:46:01,520
Speaker 1: Yeah, that's right. We don't have direct evidence for the

912
00:46:01,520 --> 00:46:04,360
Speaker 1: existence of black holes, which leaves the door open to

913
00:46:04,400 --> 00:46:07,719
Speaker 1: wondering exactly what are these objects because the argument for

914
00:46:07,760 --> 00:46:10,120
Speaker 1: black holes is essentially there's something else we can think

915
00:46:10,160 --> 00:46:12,480
Speaker 1: of that's this massive and this small, But that doesn't

916
00:46:12,520 --> 00:46:14,759
Speaker 1: mean it's not out there amazing.

917
00:46:15,400 --> 00:46:17,560
Speaker 3: All right, So time to get into science, kids, because

918
00:46:17,680 --> 00:46:19,480
Speaker 3: there's a lot of problems left to solve.

919
00:46:20,360 --> 00:46:23,000
Speaker 1: So the listeners were mostly right that the densest thing

920
00:46:23,000 --> 00:46:24,759
Speaker 1: that's not a black hole that we have observed and

921
00:46:24,800 --> 00:46:27,960
Speaker 1: have confirmation of is a neutron star. But in principle,

922
00:46:27,960 --> 00:46:30,880
Speaker 1: there could be something denser in our universe.

923
00:46:31,200 --> 00:46:41,400
Speaker 3: Way to Go Extraordinaries, Daniel and Kelly's Extraordinary Universe is

924
00:46:41,440 --> 00:46:44,640
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925
00:46:44,719 --> 00:46:47,640
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926
00:46:47,840 --> 00:46:50,480
Speaker 1: have about this Extraordinary Universe.

927
00:46:50,600 --> 00:46:53,520
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928
00:46:53,520 --> 00:46:56,520
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929
00:46:56,560 --> 00:46:56,960
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930
00:46:57,239 --> 00:47:00,759
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931
00:47:00,800 --> 00:47:04,000
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932
00:47:03,080 --> 00:47:05,120
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933
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935
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936
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