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Speaker 1: Hey, Daniel, how old are you? While I'm turning forty

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Speaker 1: seven pretty soon? Does that feel old? Too? Well? Whenever

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Speaker 1: I'm feeling old, I just decided to count my age differently.

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Speaker 1: Oh yeah, like a different base number, you know, Like

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Speaker 1: how old would I be if I lived in a

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Speaker 1: different place, For example, because Mars is years longer, I'd

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Speaker 1: be in my early twenties if I was a Martian.

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Speaker 1: But you would die in like a few hours, would

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Speaker 1: any or a few minutes if you lift the Mars

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Speaker 1: right now, depending if Elon Musk has money left from

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Speaker 1: his Twitter purchased to fund our oxygen on Mars. But

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Speaker 1: I guess even if you're a Martian, you would still

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Speaker 1: live the same amount of time, so you'd be just

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Speaker 1: as old. It'd just be a different year unit, that's right.

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Speaker 1: But it's all about how the number feels. Man. Yeah,

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Speaker 1: but also you have to take it to account your

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Speaker 1: life expectancy. That also gets changed on Mars, right yep.

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Speaker 1: On my cars we all die young anyway, or maybe not.

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Speaker 1: Maybe the air there is so much better that people

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Speaker 1: would live longer, long enough to tweet forever. Hi, I'm

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Speaker 1: Horrhand made cartoonists and the co author of frequently asked

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Speaker 1: questions about the universe. Hi, I'm Daniel. I'm a particle

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Speaker 1: physicist and a professor at U C Irvine, and I

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Speaker 1: plan to teach until my old old age. Do you

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Speaker 1: think you'll still have something to teach when you're that old?

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Speaker 1: I often teach freshman physics, which hasn't changed since Newton,

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Speaker 1: so I'm planning to teach it until I grade away.

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Speaker 1: What if you start forgetting things, even Newtonian physics? I'm

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Speaker 1: sorry would you ask? I forgot the first part of

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Speaker 1: your question, but anyways, Welcome to our podcast, Daniel and

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Speaker 1: Jorge Explain the Universe, a production of I Heart Radio,

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Speaker 1: in which we explore this incre rereadibly old and incredibly

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Speaker 1: young universe, which has lived for billions of years and

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Speaker 1: may survive for trillions and trillions more. We explore all

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Speaker 1: of the fast moving and slow paced processes that grow

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Speaker 1: and shape and define our universe and make it the

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Speaker 1: one that we love. Our goal is not to be

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Speaker 1: intimidated by the age of the universe or the billions

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Speaker 1: and trillions of years that are to come, but to

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Speaker 1: try to understand the processes that shape it, and to

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Speaker 1: explain all of them. To you, that's right, because we

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Speaker 1: live in an amazing universe that's been around for fourteen

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Speaker 1: billion years or maybe more, which sounds like a long time,

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Speaker 1: but who knows. We could be maybe in the universe's

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Speaker 1: infancy right now, and the universe might live on for

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Speaker 1: a long time, maybe even forever. Imagine if you had

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Speaker 1: lived in the universe in the first few hundred thousand years,

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Speaker 1: you might think, oh, this is what the universe is like,

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Speaker 1: not realizing that it was but the first flash of

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Speaker 1: the universe and that it would live for billions of

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Speaker 1: years with glowing stars. And now we live in the

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Speaker 1: starfield era of the universe. But it might just be

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Speaker 1: the first flash of a universe that lasts for trillions

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Speaker 1: of years and is mostly filled with black holes. So

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Speaker 1: this era of the universe could be very short lived

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Speaker 1: and very weird, weird, but also pretty cool. I think

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Speaker 1: you know right, Technically we are living in the cool

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Speaker 1: years of the universe, not the hot, crazy, insane years,

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Speaker 1: and also not the you know, super freezing years. Well,

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Speaker 1: because the universe is expanding, it's cooling, and so technically

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Speaker 1: it gets cooler every year, and not just because they

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Speaker 1: keep releasing more Marvel movies about more multiverses. Yeah, but

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Speaker 1: at some point you get it. I think it is

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Speaker 1: possible to be too cool, you know, like if the

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Speaker 1: entropy of the universe is set a maximum and the

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Speaker 1: temperature is like zero out there, Kelvin, that's not cool,

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Speaker 1: Doctor Strange, and the heat death of the universe coming soon.

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Speaker 1: I hear the last one is pretty dark, right, Everything

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Speaker 1: is getting darker. Everything in the Marvel universe is getting darker.

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Speaker 1: But in our universe, things continue to glow and brighten

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Speaker 1: and to fill the universe with photons that allow us

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Speaker 1: to see the incredible view was across billions and billions

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Speaker 1: of miles and allow our tiny human brains to grapple

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Speaker 1: with questions about how everything came to look the way

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Speaker 1: that it does and how long it will continue to shine. Yeah,

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Speaker 1: because unless you're Elon Musk, I guess the universe will

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Speaker 1: be bright and shiny and beautiful and amazing and an

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Speaker 1: open mystery pretty much until your old age. Right, is

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Speaker 1: Elon Musk going to figure it out? Is that what

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Speaker 1: you're saying. I think he's going to figure out how

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Speaker 1: to beat old age. He's going to download himself into

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Speaker 1: a Tesla and launch himself into space and live there forever.

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Speaker 1: That's right. With that, you know, special module for twittering,

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Speaker 1: Maybe he should combine all of his companies, you know, twistler,

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Speaker 1: put Twitter onto a Tesla in a boring tube and

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Speaker 1: launch that whole thing into space. That's right, Yeah, be

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Speaker 1: a Twistla X would be the company name, the Boring

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Speaker 1: twistle X. But we are not funded by Elon Musk,

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Speaker 1: although you know you know what to send your donations

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Speaker 1: Elon if you're a listener. But we are motor vated

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Speaker 1: by the desire to understand everything that's around us and

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Speaker 1: figure out exactly how long this flash in the pan

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Speaker 1: will last. Yeah, because as much as we know about

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Speaker 1: how the universe works right now, there are still open

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Speaker 1: questions about how the universe will keep on working and

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Speaker 1: how it's gonna work up until the end of the universe.

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Speaker 1: Remember that when you look up at the sky, it

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Speaker 1: seems sort of static and frozen. You don't notice from

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Speaker 1: day to day stars appearing or disappearing, or changing their location.

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Speaker 1: But that's just because we live in a tiny little

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Speaker 1: slice in the universe operates on much longer time scales.

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Speaker 1: If you could see a movie of the universe sped

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Speaker 1: up to see all fourteen billion years in just a minute,

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Speaker 1: it would seem like a crazy, chaotic, dynamic place. Even

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Speaker 1: our Solar System has had planets shift around in orbit.

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Speaker 1: Our galaxy is spinning and swirling and colliding. All sorts

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Speaker 1: of stuff is happening, and as we look out into

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Speaker 1: the universe on those cosmic scales, we ask questions about

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Speaker 1: how everything came to be and how long it will

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Speaker 1: continue to swirl and glow. Yeah, so your planet to

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Speaker 1: be a professor to you grow old or even die.

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Speaker 1: Apparently they're going to have to drag me out of

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Speaker 1: this office. I'm gonna be here until the Milky Way

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Speaker 1: stops spinning. I have a similar plan and plans to

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Speaker 1: be a cartoonis until rich I see, so another hundred

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Speaker 1: billion years. Yeah, so basically the same thing as growing

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Speaker 1: old till I die. Yeah. But anyways, it is an

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Speaker 1: interesting and growing universe, which makes me sort of wondering

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Speaker 1: how it's all going to end, If not the universe,

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Speaker 1: at least maybe our galaxy. That's right. On the podcast,

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Speaker 1: we have talked about the future of the Earth and

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Speaker 1: our Solar System, how the Earth will get subsumed eventually,

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Speaker 1: into the outer layers of the Sun. We've even talked

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Speaker 1: about the lifetime of stars, how long they will burn,

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Speaker 1: and how long our universe will keep making stars. But

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Speaker 1: the universe is not made just of planets or solar

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Speaker 1: systems or stars. One way to look at the universe

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Speaker 1: is that the basic unit are galaxies, these big swirling

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Speaker 1: swarms of billions of stars that flow through the universe.

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Speaker 1: How do galaxies form and how long do they live?

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Speaker 1: Do they just keep spinning until they become rich cartoonists?

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Speaker 1: So today we have an amazing and galactic question. Today

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Speaker 1: will be tackling how do galaxies die or how do

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Speaker 1: they fade away? I guess maybe maybe that's a nicer

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Speaker 1: way to say. How do they become emeritus galaxies? How

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Speaker 1: do they move on? How do they join the farm?

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Speaker 1: How do we make room for new galaxies because they're

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Speaker 1: just taken up space these old folks, Oh right, well,

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Speaker 1: well there's plenty of space and space right, that's true,

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Speaker 1: there is plenty of room for galaxies. But you know,

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Speaker 1: they are using the raw materials. They're occupying a whole

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Speaker 1: lot of carbon and iron, all sorts of other stuff

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Speaker 1: that could go to seed new stars and new galaxies

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Speaker 1: and new forms of life and intelligence. Well, the first

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Speaker 1: thing I thought when I saw this title was like,

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Speaker 1: what galaxies can die? I didn't know that they do.

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Speaker 1: They have like a beating heart. It depends a little

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Speaker 1: bit how you define death, right. Galaxies don't live, of course,

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Speaker 1: in the same sense that we're getic entities do the

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Speaker 1: way you and I do. But they do have a

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Speaker 1: really interesting life cycle, and at some point they stop

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Speaker 1: making stars, and eventually those stars will burn out, and

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Speaker 1: so the fate of galaxies is in fact to fade

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Speaker 1: away into darkness, which some could describe as the death

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Speaker 1: of a galaxy. I see you're defining the death of

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Speaker 1: a galaxy as when it I guess when it goes dark?

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Speaker 1: Is that what you're saying, Like when it stops shining

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Speaker 1: or we can't see it, or do you define it

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Speaker 1: there's like no activity, or when it breaks apart, or

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Speaker 1: when it turns into a black hole. There are many

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Speaker 1: possible ways to kill a galaxy. I guess there are

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Speaker 1: lots of milestones in galaxy retirement. But scientists call this

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Speaker 1: galaxy quenching. When it stops making stars, those stars burn

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Speaker 1: for a while and then eventually they will all fade out,

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Speaker 1: and you will indeed get just black holes with lumps

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Speaker 1: of stuff swirling around it. I see, So you're really

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Speaker 1: talking more about asking how do galaxies retire, like when

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Speaker 1: they start producing light? Kind of. Yah, it's not a

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Speaker 1: funeral home we're pushing these galaxies into. It's a nice

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Speaker 1: senior living facility with all sorts of other active galaxies

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Speaker 1: to hang out with. Interesting, there are cost bank retardant homes,

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Speaker 1: so you have early bird specials too. Well. Once you

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Speaker 1: no longer making stars, you're not really part of the

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Speaker 1: game anymore. Uh yeah, yeah, I guess you're you're off

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Speaker 1: the rat race kind of to see who's the Shinese galaxy.

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Speaker 1: You're definitely onto a new era in your life because

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Speaker 1: if you don't have stars, then you can't make new elements.

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Speaker 1: You're stuck with the composition that you have. Remember that

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Speaker 1: new elements are only born in the heart of stars

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Speaker 1: and supernovas and then the collisions of neutron stars. But

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Speaker 1: once you've stopped making stars, you're no longer initiating that

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Speaker 1: process that ends up with new elements, and so eventually

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Speaker 1: you're going to get stuck with whatever you have. You'd

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Speaker 1: be sort of frozen with your mixture of stuff. All right, Well,

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Speaker 1: we'll get into the details of galaxies retirement, both from

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Speaker 1: its job and mainly from its life. But as usually,

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Speaker 1: we were wondering how many people had had these dark

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Speaker 1: thoughts about galaxies and what happens to them in the future.

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Speaker 1: So it's usual Daniel went out there and ask people

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Speaker 1: a question, how do galaxies die? So thanks everybody who

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Speaker 1: participates in these one questions. If you'd like to hear

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Speaker 1: your speculations here on the podcast for everybody else to enjoy,

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Speaker 1: please don't be shy right to us two questions at

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Speaker 1: Daniel and Jorge dot com. Think about it for a second,

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Speaker 1: how do you think galaxies retired? Here's what people had

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Speaker 1: to say. I think I have a decent guest for this.

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Speaker 1: There are supermassive the black holes at the center of

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Speaker 1: every galaxy, and at some point black holes do die

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Speaker 1: or evaporate. Rather, it is possible. So maybe when that happens,

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Speaker 1: when the black hole kind of doesn't exist anymore than

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Speaker 1: the galaxies just disindigates. As far as I know, galaxies

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Speaker 1: die when their stares start dying and stop making more

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Speaker 1: stories and and it just becomes a cold cloud of

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Speaker 1: sadness and you can't see it. So I guess that's

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Speaker 1: a dead galaxy. I don't know how galaxies die. I

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Speaker 1: would guess that either the if it's a black hole

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Speaker 1: in the middle of the galaxy, that it as opposed

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Speaker 1: to swallows large parts of the of the galaxy, or

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Speaker 1: that stars either you should have died by not admitting

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Speaker 1: as much light as they previously would have been, and

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Speaker 1: so the galaxy becomes sort of darker and darker. So

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Speaker 1: I think galaxies are so large and have so much

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Speaker 1: angular momentum that all the stars within the galaxy will

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Speaker 1: reach the end stages of their life and we will

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Speaker 1: no longer have the starting conditions necessary to get new

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Speaker 1: stars created before the entire galaxy will be eaten up

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Speaker 1: by the supermassive black hole. Galaxies die in three ways,

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Speaker 1: first when they crash in and merge with a larger galaxy,

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Speaker 1: second when the stars fall in to the black hole

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Speaker 1: at the center of the galaxy, and third when the

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Speaker 1: galaxy creates no news stars and the stars and the

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Speaker 1: galaxy die from old age. The galaxies die if eventually

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Speaker 1: they lose the ability to make new stars. So this

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Speaker 1: can come from a different reasons, but one of them

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Speaker 1: that I know it might be that the black hole

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Speaker 1: from the center of the galaxy starts this process by

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Speaker 1: emitting probably powerful cluss or mm hmm, the supermassive black

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Speaker 1: holes in the center suck them up or something. All right,

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Speaker 1: dark answers for a dark question. I guess a lot

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Speaker 1: of people went for the black hole scenario. Yeah, that's

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Speaker 1: really interesting. People are aware that eventually everything will fall

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Speaker 1: into the black hole and imagine that that's what's going

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Speaker 1: to kill all the galaxy. But little do they know

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Speaker 1: there's something worth around the corner or what. Yeah, there's

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Speaker 1: sort of two competing timelines. They're like, will the stars

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Speaker 1: burn out, will it stop making stars before it falls

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Speaker 1: into the black hole? Or will the black hole like

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Speaker 1: eat up a bunch of otherwise lively elements of the

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Speaker 1: galaxy which could have made new stars if only they

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Speaker 1: hadn't fallen into that gravitational Well, all right, Well, before

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Speaker 1: we start to consider a galaxy's death, let's um, you know,

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Speaker 1: let's do a little retrospective here, and let's consider the

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Speaker 1: whole life of the galaxy. So let's start at getting Daniel,

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Speaker 1: how did galaxies even get born? Yeah, I like that

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Speaker 1: we begin with the nostalgic so like montage, musical mona,

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Speaker 1: all the good moments, remember those with an old timey

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Speaker 1: like film field, something soft focus, you know, fuzzy pictures

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Speaker 1: of the galaxy playing in the kiddie pool, like the

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Speaker 1: projector sounds quit, the galaxy being mean to the cat,

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Speaker 1: you know, that kind of stuff, but looking so cute.

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Speaker 1: No pictures of the galaxy crying or I think of

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Speaker 1: galaxies is one of the most fundamental units of the

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Speaker 1: universe because even though the stars are within them, it's

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Speaker 1: the galaxies that are formed by like the initial fluctuations.

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Speaker 1: So you know, you begin at the very very early

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Speaker 1: stages of the universe, everything is smooth and filled with matter.

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Speaker 1: There's no wiggles, there's no extra lumpy bits. And then

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Speaker 1: you get quantum mechanics that fluctuates and gives you like

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Speaker 1: a little bit more stuff here, maybe fewer particles over here.

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Speaker 1: That's really tiny, that's super microscopic. That kind of quantum

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Speaker 1: fluctuation is happening all the time, even today. But the

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Speaker 1: very early universe, those fluctuations were blown up to a

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Speaker 1: huge scale by early universe inflation. The way space itself

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Speaker 1: was stretched by like a factor of ten to the

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Speaker 1: thirty blew up these little tiny lumps, these little bits

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Speaker 1: where something was heavier and something was lighter into actual

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Speaker 1: macroscopic sizes. And then gravity took over and it said,

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Speaker 1: all right, this spot is a little bit denser than

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Speaker 1: that spot, so all the particles are going to get

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Speaker 1: attracted over there. So you begin with these very shallow

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Speaker 1: gravitational wells that slowly roll more particles into them, and

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Speaker 1: then they get stronger and stronger and stronger. We're talking

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Speaker 1: about it's mostly dark matter. It builds these gravitational wells

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Speaker 1: that then normal matter falls into, and where you have

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Speaker 1: these wells, you have big blobs of matter and that's

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Speaker 1: what forms galaxies. Yeah, I think we start talk about

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Speaker 1: it as the seeds of the galaxies, right, Like the seeds,

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Speaker 1: like where the galaxies came from, was all sort of

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Speaker 1: laid out in those first moments of the Big Bang,

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Speaker 1: so kind of in a way like galaxies were maybe

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Speaker 1: the first things that were defined in the universe, the

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Speaker 1: first kind of organization, right, Yeah, you can think about

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Speaker 1: it like that. We think that probably stars formed and

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Speaker 1: then they formed into galaxies, but they all formed out

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Speaker 1: of these big clouds of gas that were themselves formed

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Speaker 1: by these dark matter halos, which were themselves formed by

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Speaker 1: those initial seeds that we talked about. Something I think

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Speaker 1: is really cool is that the pattern of dark matter,

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Speaker 1: which controls the whole structure of the universe, is like

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Speaker 1: these filaments, you know, these like lines of through a

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Speaker 1: cosmic web, and where those filaments overlap with each other

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Speaker 1: are the dark matter halos. You can think of it

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Speaker 1: sort of like these filaments are funneling matter into these

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Speaker 1: lakes which are where they intersect, and so gas is

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Speaker 1: falling from these filaments into these halos and then swirling

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Speaker 1: together to form stars which form galaxies. Interesting. I guess

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Speaker 1: what I mean is like if you had been around

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Speaker 1: at that time, that early in the universe, you could

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Speaker 1: have been predicted maybe like, oh, there's gonna be a galaxy,

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Speaker 1: and there's gonna be a galaxy, you know what I mean,

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Speaker 1: Like the definition of a galaxy was sort of right

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Speaker 1: there at the beginning of the universe. Yeah, you definitely

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Speaker 1: would know that this is where complex structure is going

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Speaker 1: to form. I think it's super fascinating what you end

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Speaker 1: up getting. I mean, you start with just clouds of hydrogen,

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Speaker 1: and then like you get stars and you get galaxies.

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Speaker 1: It's really fascinating sort of the size and the scale

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Speaker 1: and the shape of what forms out of that. It's

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Speaker 1: one of the I think the deepest questions in modern physics.

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Speaker 1: Why these objects emerge at these scales? You know, why

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Speaker 1: do we get stars there about this size? Why do

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Speaker 1: we galaxies about this size? Why don't we get just

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Speaker 1: one humongous galaxy in the whole universe? Or why do

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Speaker 1: galaxies form at all? Why don't we just have stars

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Speaker 1: spread out everywhere? So I think it would have been

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Speaker 1: pretty hard to predict computationally. I think it's really interesting

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Speaker 1: to sort of see what emerges from structure in the universe.

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Speaker 1: And that's just what we're doing now. We're still seeing

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Speaker 1: structure emerged. Now we have clusters of galaxies and superclusters

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Speaker 1: of galaxies, and that process is still happening because we're

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Speaker 1: still fairly young in the universe. Yeah we are. Are

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Speaker 1: we still in there like the teenage years? You think,

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Speaker 1: the awkward teenage years full of pimples. Well, gravity is

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Speaker 1: really slow, so it takes a long time to form structure,

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Speaker 1: and so it's formed galaxies and galaxy clusters. But those

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Speaker 1: galaxy clusters themselves are like very loosely grouped into superclusters.

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Speaker 1: Gravity hasn't had time really to gather that together into

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Speaker 1: something greater. In the meantime, dark energy is doing the

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Speaker 1: opposite job. It's pushing everything apart, preventing gravity from making superstructures.

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Speaker 1: So we might be living in the moment when the

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Speaker 1: universe is the most organized. So I don't know if

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Speaker 1: those are really the teenage years or that's like it's

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Speaker 1: mid thirties. You know, it's really sort of on top

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Speaker 1: of its stuff before it starts to get old, before

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Speaker 1: it has its midlife crisis. We all do exactly all right, Well,

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Speaker 1: I guess that's the birth of a galaxy and so

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Speaker 1: and a surprising idea is that galaxies change and they

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Speaker 1: might even die one day. So let's dive right into that.

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Speaker 1: But first, let's take a quick break. All right, we're

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Speaker 1: talking about the death of galaxies, Daniel, Does that mean

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Speaker 1: our galaxy is gonna die? Scientists think that the Milky

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Speaker 1: Way itself is beginning to quench. We're entering a period

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Speaker 1: we're making fewer and fewer stars, and that's going to

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Speaker 1: happen faster and faster, so sort of the milky ways

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Speaker 1: peak might be behind us. Oh boy, well, for a second,

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Speaker 1: I thought you were going to give it a super

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Speaker 1: plot twist and say like, oh, our galaxy is already dead.

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Speaker 1: It's been dead the whole time, where it's just ghosts.

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Speaker 1: That's right, This whole galaxy is nothing but an m

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Speaker 1: Night shun Land film. Yeah, spoiler alert. I talked to

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Speaker 1: dead galaxies. I see that galaxies with my telescopes. Do

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Speaker 1: you kind of do maybe? Right, Like if you look

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Speaker 1: at into the far universe, you might be seeing galaxies

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Speaker 1: that have died already. Right, We do see a lot

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Speaker 1: of galaxies that aren't dead. And one of the surprising

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Speaker 1: things with something we struggle to understand is what's killing

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Speaker 1: all these galaxies? Why are there so many galaxies out

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Speaker 1: there that are already quenched and have stopped making new stars.

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Speaker 1: It just went from a thriller to a mystery. We

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Speaker 1: just switched genres here. It's a combination because somebody is

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Speaker 1: still out there killing galaxies. It's not over yet. We

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Speaker 1: still have a chance to catch the killer and maybe

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Speaker 1: save future galaxies and maybe do nothing about it because

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Speaker 1: because just physics, physics, are you saying we can't learn

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Speaker 1: things about the universe and intervene in its faith that

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Speaker 1: we have no control, no power to change the future

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Speaker 1: of humanity. That doesn't sound like an engineer, you tell me.

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Speaker 1: I guess you know, the physicist has to tell us

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Speaker 1: if it's possible. Well, the first thing to do is

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Speaker 1: to understand what it is that's clean these galaxies, and

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Speaker 1: then we can figure out if it's possible to intervene.

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Speaker 1: Then we have to start training some galaxy engineers. That

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Speaker 1: might be the sequel. I guess all right, Well, I

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Speaker 1: think one interesting bit of news is that, you know,

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Speaker 1: galaxies seem to change, and I guess they quention they

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Speaker 1: maybe eventually die. And so is that something that we've

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Speaker 1: always believed in, that galaxies can change or did we

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Speaker 1: think that we just you know, swirl around forever. We've

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Speaker 1: always thought that eventually galaxies would use up their raw

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Speaker 1: materials in terms of making stars. You know, you have

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Speaker 1: a certain amount of hydrogen in the universe, for example,

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Speaker 1: that's primarily what's burned to make stars. Eventually you will

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Speaker 1: run out of them. We have a podcast episode about

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Speaker 1: how many generations of stars will there be? Because you know,

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Speaker 1: stars don't live forever, and eventually they explode and spew

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Speaker 1: their materials back out in the universe, which gets gathered

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Speaker 1: back together. But we don't think that can happen forever.

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Speaker 1: So we've always known that eventually waves of star formation

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Speaker 1: will end. But we were surprised when we looked at

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Speaker 1: the galaxies and discovered how many are already dead, how

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Speaker 1: many have stopped making stars well before we expected them

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Speaker 1: too interesting. Yeah, I guess you know, there's a limited

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Speaker 1: supply of fuel in the universe, right, and at some

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Speaker 1: point we run out, like we have a gas tank

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Speaker 1: kind of and you know, hydrogen gets you stop, gets

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Speaker 1: turned into heavier element, and then to break it apart,

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Speaker 1: you need extra energy. Yeah, there's two things that drive this.

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Speaker 1: One is you need to have the fuel, and the

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Speaker 1: other is that the fuel has to have the right conditions.

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Speaker 1: Like it's not just enough to have hydrogen. You have

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Speaker 1: to have hydrogen in the right situation in order to

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Speaker 1: get a star to form. And the key thing to

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Speaker 1: making stars form is that you need huge blobs of

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Speaker 1: cold hydrogen. If you have hydrogen but it's really hot,

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Speaker 1: it's not going to form a star because remember that

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Speaker 1: gravity is super duper weak in order to tug things

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Speaker 1: together to make a star, the particles have to be

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Speaker 1: very slow moving. If your gas is heated up too much,

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Speaker 1: then gravity is not going to be able to pull

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Speaker 1: it together to make a star. All right, Well that's

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Speaker 1: the birth of a galaxy that I guess that's how

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Speaker 1: they start, right, They start for influctuations and the universe

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Speaker 1: and the dark matter sees which pull in stuff, and

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Speaker 1: then galaxies form. That's just kind of the beginning of

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Speaker 1: the story. Right. Eventually galaxies also merged, and our thinking

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Speaker 1: there has changed also. Originally, we looked out at the

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Speaker 1: universe and we saw really big galaxies, mostly because that's

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Speaker 1: all we could see because they were brighter, and we thought,

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Speaker 1: oh wow, maybe these really big galaxies sort of form

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Speaker 1: all at once, like monolithic collapse of a huge cloud

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Speaker 1: of gas into a swirling disc. But then as we

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Speaker 1: developed the technology look further and further into the universe

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Speaker 1: and earlier and earlier back in time, we discovered a

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Speaker 1: lot more galaxies that were much smaller, and we realized

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Speaker 1: that the story of galaxy formation is more complicated. Instead

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Speaker 1: of having really big galaxies form at once, it turns

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Speaker 1: out it's much more likely to form a bunch of

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Speaker 1: small galaxy then have those merged together. The galaxies are

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Speaker 1: doing a lot of merging. Most of the galaxies we

430
00:23:05,640 --> 00:23:07,760
Speaker 1: see how there are actually the products of lots of

431
00:23:07,800 --> 00:23:11,200
Speaker 1: little baby galaxies that came together to make a bigger galaxy.

432
00:23:11,720 --> 00:23:13,440
Speaker 1: I say, it's like we looked at into the universe

433
00:23:13,440 --> 00:23:17,520
Speaker 1: and saw more babies baby galaxies than we expect. It

434
00:23:17,560 --> 00:23:19,960
Speaker 1: is that kind of the idea, which I guess would

435
00:23:20,000 --> 00:23:23,760
Speaker 1: then logically mean the bigger galaxies don't inform. They they're

436
00:23:23,800 --> 00:23:27,400
Speaker 1: the result of two baby galaxies merging exactly where multiple

437
00:23:27,400 --> 00:23:30,840
Speaker 1: baby galaxies merging. It also helps explain the shape of

438
00:23:30,840 --> 00:23:34,520
Speaker 1: these galaxies, like when an individual galaxy forms, it tends

439
00:23:34,520 --> 00:23:36,840
Speaker 1: to form as a disk to give a big cloud

440
00:23:36,840 --> 00:23:39,240
Speaker 1: of gas, and it's spinning a certain way, and that

441
00:23:39,359 --> 00:23:42,920
Speaker 1: spin prevented from collapsing in one direction, but gravity can

442
00:23:42,960 --> 00:23:45,119
Speaker 1: collapse it in the other direction, which is why you

443
00:23:45,160 --> 00:23:48,080
Speaker 1: get a disc. So disc galaxies tend to have formed

444
00:23:48,080 --> 00:23:51,080
Speaker 1: from a single cloud of gas and dust with some spin.

445
00:23:51,280 --> 00:23:53,680
Speaker 1: But then when two of these things merge, they come

446
00:23:53,720 --> 00:23:56,520
Speaker 1: in with different shapes and different sizes and different disks,

447
00:23:56,720 --> 00:23:59,680
Speaker 1: and that's how you get like elliptical galaxies and things

448
00:23:59,680 --> 00:24:02,359
Speaker 1: that are are rounded because you're combining like the spin

449
00:24:02,440 --> 00:24:05,840
Speaker 1: of two disc galaxies together. So the idea is that

450
00:24:05,880 --> 00:24:09,040
Speaker 1: the bigger elliptical galaxies are formed from a bunch of

451
00:24:09,080 --> 00:24:12,399
Speaker 1: smaller disc galaxies that came together. For example, the Milky

452
00:24:12,440 --> 00:24:14,959
Speaker 1: Way and Andromeda are going to collide, but they're not

453
00:24:15,040 --> 00:24:17,320
Speaker 1: spinning in the same direction, So you're not going to

454
00:24:17,480 --> 00:24:19,840
Speaker 1: end up with one big disc galaxy. You're gonna endup

455
00:24:19,840 --> 00:24:23,879
Speaker 1: with something more elliptical that has like two spin axes. Interesting,

456
00:24:23,960 --> 00:24:26,600
Speaker 1: so a lot more of the galaxies foreign from merging

457
00:24:26,680 --> 00:24:29,720
Speaker 1: than we thought before. I guess why do we have

458
00:24:29,840 --> 00:24:32,280
Speaker 1: that wrong impression? But we had the wrong impression just

459
00:24:32,320 --> 00:24:34,440
Speaker 1: because we didn't see a lot of these baby galaxies

460
00:24:34,480 --> 00:24:36,840
Speaker 1: early on. You know, we didn't have the technology before

461
00:24:36,920 --> 00:24:39,760
Speaker 1: Hubble and those kinds of telescopes. We just couldn't see them.

462
00:24:39,760 --> 00:24:42,440
Speaker 1: But when Hubble looked really deep into the universe and

463
00:24:42,480 --> 00:24:45,720
Speaker 1: discovered how many galaxies are out there, that's when we

464
00:24:45,760 --> 00:24:48,919
Speaker 1: got the clue. Is from seeing these baby galaxies in

465
00:24:48,960 --> 00:24:51,800
Speaker 1: the early universe. You know, the number of galaxies out

466
00:24:51,800 --> 00:24:54,040
Speaker 1: there is sort of amazing. If you hold up your

467
00:24:54,080 --> 00:24:57,000
Speaker 1: pinky at arms length, then the part of your sky

468
00:24:57,359 --> 00:25:01,000
Speaker 1: blocked by your fingernail, and your pinky contains about a

469
00:25:01,200 --> 00:25:05,240
Speaker 1: million galaxies in the observable universe, you know, layered further

470
00:25:05,320 --> 00:25:07,359
Speaker 1: and further and back in space and time. And so

471
00:25:07,440 --> 00:25:10,240
Speaker 1: now like scan your pinky around the whole sky. Each

472
00:25:10,280 --> 00:25:13,520
Speaker 1: of those is a million galaxies. So there's an incredible

473
00:25:13,600 --> 00:25:15,920
Speaker 1: number out there, and now we have a huge population

474
00:25:15,960 --> 00:25:18,280
Speaker 1: to study, so we get a better sense of how

475
00:25:18,320 --> 00:25:20,919
Speaker 1: these things have evolved. Well, that's wild. What if I

476
00:25:20,960 --> 00:25:25,280
Speaker 1: let my pinky fingernailk and grow, then you're containing more

477
00:25:25,320 --> 00:25:28,119
Speaker 1: and more galaxies. You're becoming master of even more of

478
00:25:28,119 --> 00:25:31,800
Speaker 1: space and time, a pinky master. I guess, all right,

479
00:25:31,840 --> 00:25:34,320
Speaker 1: So that's uh, I guess that's the basic of the

480
00:25:34,400 --> 00:25:37,320
Speaker 1: life of a galaxy right there. Born as little baby galaxies,

481
00:25:37,400 --> 00:25:39,480
Speaker 1: they grow up to be a teenager as they start

482
00:25:39,560 --> 00:25:42,160
Speaker 1: hooking up doing inappropriate things, and then they merge into

483
00:25:42,200 --> 00:25:45,480
Speaker 1: bigger galaxies and then they keep burning for a while.

484
00:25:45,600 --> 00:25:48,320
Speaker 1: I guess, like, what's the average age of a galaxy?

485
00:25:48,400 --> 00:25:51,400
Speaker 1: Galaxies are really old, like the Milky Way is almost

486
00:25:51,440 --> 00:25:54,159
Speaker 1: as old as the universe. Galaxies formed very early on

487
00:25:54,200 --> 00:25:55,879
Speaker 1: a lot of them in the first billion years of

488
00:25:55,960 --> 00:25:58,440
Speaker 1: the universe. Many of them are more than ten billion

489
00:25:58,520 --> 00:26:02,000
Speaker 1: years old. But at some point, as you say, they die,

490
00:26:02,240 --> 00:26:05,520
Speaker 1: they stop shining, they stop making stars, they quench. So

491
00:26:05,920 --> 00:26:09,280
Speaker 1: I guess, Daniel, what's the process for a galaxy to die?

492
00:26:09,359 --> 00:26:11,440
Speaker 1: So for a galaxy to die, for to stop being

493
00:26:11,480 --> 00:26:15,080
Speaker 1: able to make stars, something has to heat up its gas,

494
00:26:15,119 --> 00:26:18,560
Speaker 1: something has to prevent its gas from staying cold, because

495
00:26:18,560 --> 00:26:21,280
Speaker 1: in order to form stars, you need that cold gas,

496
00:26:21,640 --> 00:26:24,160
Speaker 1: and some of the star formation comes from the original

497
00:26:24,200 --> 00:26:26,879
Speaker 1: gas that the galaxy started with, whatever was in that

498
00:26:26,960 --> 00:26:30,199
Speaker 1: dark matter halo. Remember, the galaxies are not really alone

499
00:26:30,200 --> 00:26:32,920
Speaker 1: in the universe. They're sort of like at the intersections

500
00:26:32,960 --> 00:26:36,680
Speaker 1: of these dark matter filaments. So there's also sometimes new

501
00:26:36,760 --> 00:26:40,960
Speaker 1: gas falling into these galaxies along those filaments, like tributaries

502
00:26:41,000 --> 00:26:43,560
Speaker 1: to a lake, and so galaxies can also continue to

503
00:26:43,600 --> 00:26:47,480
Speaker 1: form stars as they suck in more gas from these filaments.

504
00:26:47,960 --> 00:26:51,080
Speaker 1: So the way a galaxy dies is somehow losing access

505
00:26:51,119 --> 00:26:53,600
Speaker 1: to that new gas or blowing out the cold gas,

506
00:26:53,720 --> 00:26:56,400
Speaker 1: or heating up the cold gas that's inside it, because

507
00:26:56,440 --> 00:26:59,720
Speaker 1: remember you need cold gas to make star I see,

508
00:26:59,720 --> 00:27:01,840
Speaker 1: all right, So you're defining the death of a galaxy

509
00:27:01,920 --> 00:27:05,480
Speaker 1: is when it stops forming new stars. Is that, I

510
00:27:05,520 --> 00:27:08,880
Speaker 1: guess the definition. But even if it stops forming stars,

511
00:27:08,960 --> 00:27:12,320
Speaker 1: it's still shining though, right. Astronomers don't talk about galaxies dying.

512
00:27:12,400 --> 00:27:15,320
Speaker 1: They use the technical term quenching, which means it stopped

513
00:27:15,359 --> 00:27:17,879
Speaker 1: forming new stars. But you're right, even if it stopped

514
00:27:17,920 --> 00:27:20,760
Speaker 1: forming any stars at all, those stars themselves can burn

515
00:27:20,880 --> 00:27:24,320
Speaker 1: for billions and billions, for sometimes even trillions of years.

516
00:27:24,720 --> 00:27:28,399
Speaker 1: Remember that stars their lifetime depends on their size, so

517
00:27:28,520 --> 00:27:31,760
Speaker 1: really big stars don't burn very long, and really small

518
00:27:31,840 --> 00:27:35,040
Speaker 1: stars will burn for a very very long time. So

519
00:27:35,080 --> 00:27:38,400
Speaker 1: even a galaxy that's totally quenched won't make any new stars,

520
00:27:38,440 --> 00:27:40,640
Speaker 1: but those stars will continue to burn for a very

521
00:27:40,680 --> 00:27:42,919
Speaker 1: long time. Oh, I see, I see what's going on.

522
00:27:42,960 --> 00:27:44,719
Speaker 1: I think really, what you mean to ask is how

523
00:27:44,760 --> 00:27:50,880
Speaker 1: do galaxies peak? Or like, how do galaxies stop getting brighter? Maybe? Right? Yeah,

524
00:27:50,960 --> 00:27:54,359
Speaker 1: exactly how do they stop having any babies? I see,

525
00:27:54,160 --> 00:27:55,840
Speaker 1: I think I see what's going on here, Daniel. I

526
00:27:55,880 --> 00:28:00,280
Speaker 1: think you associate not working with dying. That's why never

527
00:28:00,280 --> 00:28:07,480
Speaker 1: gonna entire. Yeah, you're never gonna retire, like if you

528
00:28:07,560 --> 00:28:10,760
Speaker 1: retire or die, like if a professor stops making papers,

529
00:28:10,760 --> 00:28:13,600
Speaker 1: that's that's like that for them, who even are you

530
00:28:13,720 --> 00:28:17,600
Speaker 1: anymore in that situation? But yeah, just to becular, that's

531
00:28:17,640 --> 00:28:20,320
Speaker 1: kind of what we're saying, right, Like, the galaxies don't

532
00:28:20,359 --> 00:28:23,080
Speaker 1: maybe I guess they will at some point grow dark,

533
00:28:23,119 --> 00:28:25,240
Speaker 1: But here today, what we're talking about is like how

534
00:28:25,240 --> 00:28:28,320
Speaker 1: do galaxies peak or how when did they stop being

535
00:28:28,359 --> 00:28:31,680
Speaker 1: active exactly? And as we look out into the universe,

536
00:28:31,960 --> 00:28:35,840
Speaker 1: we can tell whether galaxies are still making stars or not.

537
00:28:36,359 --> 00:28:38,760
Speaker 1: And we do that, we see some pretty surprising things

538
00:28:38,800 --> 00:28:42,440
Speaker 1: about what's going on with all the galaxies in the universe. Wait,

539
00:28:42,520 --> 00:28:46,160
Speaker 1: that's kind of weird because I guess you were defining

540
00:28:46,200 --> 00:28:48,800
Speaker 1: death as stopping production of stars. You need to like

541
00:28:48,920 --> 00:28:51,400
Speaker 1: know how many news stars are being made and right,

542
00:28:52,000 --> 00:28:54,600
Speaker 1: but how do you tell that on a short human life.

543
00:28:55,640 --> 00:28:57,520
Speaker 1: So it's not that we look at the galaxies and

544
00:28:57,560 --> 00:28:59,400
Speaker 1: we count the stars and we say, oh, look, it's

545
00:28:59,440 --> 00:29:02,040
Speaker 1: still making more because these galaxies, a lot of them

546
00:29:02,080 --> 00:29:04,560
Speaker 1: are really far away. All we can see them is

547
00:29:04,600 --> 00:29:07,200
Speaker 1: like a pixel or two on the hubble. But what

548
00:29:07,280 --> 00:29:09,440
Speaker 1: we can do is look at the color of the

549
00:29:09,560 --> 00:29:13,240
Speaker 1: light that comes from these galaxies, and that tells us

550
00:29:13,600 --> 00:29:16,440
Speaker 1: about whether or not there are new young stars in

551
00:29:16,520 --> 00:29:19,600
Speaker 1: the galaxy. And the reason is that new young stars

552
00:29:19,920 --> 00:29:22,960
Speaker 1: means hot stars. When stars are formed, you get big

553
00:29:23,000 --> 00:29:25,360
Speaker 1: ones and you get small ones. But the big ones,

554
00:29:25,440 --> 00:29:27,960
Speaker 1: the ones that burn hot, that burn blue, they don't

555
00:29:28,040 --> 00:29:30,000
Speaker 1: last for very long. So if you're looking at a

556
00:29:30,000 --> 00:29:33,080
Speaker 1: galaxy and you're seeing blue light from it, that means

557
00:29:33,280 --> 00:29:36,440
Speaker 1: recently formed stars. You're looking at a galaxy and you

558
00:29:36,600 --> 00:29:41,280
Speaker 1: only see red light, that means cooler stars, only older stars,

559
00:29:41,320 --> 00:29:44,600
Speaker 1: no recently formed stars. So by looking at the color

560
00:29:44,640 --> 00:29:46,800
Speaker 1: of the light from the galaxy, you can tell if

561
00:29:46,800 --> 00:29:49,720
Speaker 1: there are recently formed stars in it, because they recently

562
00:29:49,720 --> 00:29:54,080
Speaker 1: formed ones burn hotter and burn bluer. Interesting, you're saying

563
00:29:54,120 --> 00:29:58,680
Speaker 1: that galaxies kind of peak they start producing new stars

564
00:29:58,720 --> 00:30:01,320
Speaker 1: when they turn from to it a red exactly blue

565
00:30:01,320 --> 00:30:04,959
Speaker 1: means you've recently produced some stars, because only young stars

566
00:30:05,000 --> 00:30:07,720
Speaker 1: are ever blue, because blue stars don't last very long,

567
00:30:07,840 --> 00:30:10,320
Speaker 1: and eventually all your blue stars burn out and all

568
00:30:10,360 --> 00:30:13,040
Speaker 1: you're left with our red stars. So if you're an

569
00:30:13,040 --> 00:30:15,840
Speaker 1: all red galaxy, it means you haven't made anything recently.

570
00:30:16,520 --> 00:30:18,760
Speaker 1: I feel like that's like people these days. You know,

571
00:30:18,920 --> 00:30:21,800
Speaker 1: everyone starts out as a democrat and liberal, but then

572
00:30:21,840 --> 00:30:24,280
Speaker 1: they get more conservative and red and the old age,

573
00:30:24,880 --> 00:30:27,240
Speaker 1: you know, maybe we should avoid the political analogy and

574
00:30:27,280 --> 00:30:29,600
Speaker 1: think about like musicians. You know, are you a musician

575
00:30:29,640 --> 00:30:32,280
Speaker 1: that keeps putting out new albums or you just like

576
00:30:32,320 --> 00:30:37,200
Speaker 1: the Beatles, you're just making money on your old catalog. Well,

577
00:30:37,200 --> 00:30:39,480
Speaker 1: the Beatles came out with the white album, so I

578
00:30:39,480 --> 00:30:41,719
Speaker 1: don't know you fit them into the color spectrum. Well,

579
00:30:41,760 --> 00:30:43,840
Speaker 1: the fascinating thing is when you look at this color spectrum,

580
00:30:44,080 --> 00:30:46,560
Speaker 1: you see some that are still making new stars. You

581
00:30:46,600 --> 00:30:50,160
Speaker 1: see a whole huge number that are already quenched, many

582
00:30:50,240 --> 00:30:53,520
Speaker 1: more than we expect, and you see very very few

583
00:30:53,720 --> 00:30:56,400
Speaker 1: in between, very few in this region they called the

584
00:30:56,480 --> 00:30:59,760
Speaker 1: green valley, between the blue and the red, the ones

585
00:30:59,760 --> 00:31:02,520
Speaker 1: that are like quenching. So there's a bunch that are

586
00:31:02,560 --> 00:31:05,440
Speaker 1: not quenched. Is a huge number that have been quenched,

587
00:31:05,440 --> 00:31:09,640
Speaker 1: and very few in the process of quenching. Interesting. Yeah,

588
00:31:09,880 --> 00:31:12,040
Speaker 1: as you said, it's a big mystery. And so let's

589
00:31:12,080 --> 00:31:15,720
Speaker 1: dive into that mystery of what is killing or I guess,

590
00:31:15,720 --> 00:31:19,520
Speaker 1: retiring all the stars in the universe. But first let's

591
00:31:19,560 --> 00:31:34,880
Speaker 1: take another quick break. Alright, we're talking about um, I

592
00:31:34,920 --> 00:31:39,200
Speaker 1: guess when Galaxy has changed their political views? Right, when

593
00:31:39,240 --> 00:31:43,320
Speaker 1: galaxies stopped recording albums when they stopped polishing papers, which

594
00:31:43,320 --> 00:31:46,520
Speaker 1: according to professors, is the same as death. Like give

595
00:31:46,520 --> 00:31:49,640
Speaker 1: me research or give me death. What if galaxies get

596
00:31:49,640 --> 00:31:52,560
Speaker 1: a hobby, then they won't see retirement as death anymore.

597
00:31:52,680 --> 00:31:55,000
Speaker 1: I do see a lot of Americans professors still around

598
00:31:55,000 --> 00:31:56,960
Speaker 1: the department, and I wonder, like, why do you still

599
00:31:56,960 --> 00:31:59,400
Speaker 1: come in every day? And I think, you know, maybe

600
00:31:59,400 --> 00:32:01,520
Speaker 1: their partners at home and don't really want them hanging

601
00:32:01,520 --> 00:32:04,520
Speaker 1: out doing their hobbies at home. You know, they're probably

602
00:32:04,520 --> 00:32:06,560
Speaker 1: thought the same thing you youth are thinking right now,

603
00:32:06,560 --> 00:32:08,200
Speaker 1: and you're like, they're gonna have to drag me out,

604
00:32:08,760 --> 00:32:11,200
Speaker 1: drag me out, or call the grim Reaper. I guess.

605
00:32:11,600 --> 00:32:14,400
Speaker 1: But apparently galaxies do retire. At some point, they peaked,

606
00:32:14,440 --> 00:32:17,880
Speaker 1: they stopped making news stars, and I guess it shows

607
00:32:17,920 --> 00:32:20,440
Speaker 1: on a galaxy, you know, like it's pretty. It sounds

608
00:32:20,440 --> 00:32:23,160
Speaker 1: like it's pretty obvious, Like if a galaxy is pretty blue,

609
00:32:23,200 --> 00:32:26,040
Speaker 1: then if it's pretty red, it's old exactly. And there

610
00:32:26,040 --> 00:32:29,280
Speaker 1: are very few galaxies in between, which suggests that this

611
00:32:29,360 --> 00:32:33,400
Speaker 1: process of quenchya galaxy happens rapidly. You're not in the

612
00:32:33,440 --> 00:32:35,880
Speaker 1: Green Valley for very long on your trip from blue

613
00:32:35,880 --> 00:32:38,200
Speaker 1: to red. Well, it's sort of like when you run

614
00:32:38,240 --> 00:32:40,920
Speaker 1: out of gas in your car. It's not a gradual process,

615
00:32:41,040 --> 00:32:44,640
Speaker 1: like once you run out of gas, your car stops. Yeah,

616
00:32:44,680 --> 00:32:46,680
Speaker 1: Like the galaxies are huge, right, you might imagine that

617
00:32:46,720 --> 00:32:48,640
Speaker 1: one part of it might quench, another part of it

618
00:32:48,720 --> 00:32:51,080
Speaker 1: might still be active. But it seems to happen on

619
00:32:51,200 --> 00:32:54,600
Speaker 1: sort of a galaxy wide scale, all at once. Well,

620
00:32:54,680 --> 00:32:57,840
Speaker 1: let's recap a little bit here. You said the galaxies peak,

621
00:32:57,960 --> 00:33:00,719
Speaker 1: they start producing new stars when they run out of gas.

622
00:33:01,200 --> 00:33:03,120
Speaker 1: And you said that it's not because you run out

623
00:33:03,160 --> 00:33:05,720
Speaker 1: of hydrogen gas, but because you run out of cold

624
00:33:05,840 --> 00:33:09,000
Speaker 1: hydrogen gas. In order to form stars, you need clouds

625
00:33:09,040 --> 00:33:11,680
Speaker 1: of cold gas that gravity can work on to pull

626
00:33:11,760 --> 00:33:14,760
Speaker 1: together to make those stars. And so it might be

627
00:33:14,800 --> 00:33:17,280
Speaker 1: that there's plenty of hydrogen left in those galaxies. We

628
00:33:17,320 --> 00:33:19,440
Speaker 1: suspect that there might be. It might just be that

629
00:33:19,520 --> 00:33:22,280
Speaker 1: it's too hot, So either you lose the gas or

630
00:33:22,360 --> 00:33:25,080
Speaker 1: the gas gets too hot. Those are the ideas for

631
00:33:25,120 --> 00:33:27,680
Speaker 1: how to quench a galaxy. Wait, what happens if it

632
00:33:27,680 --> 00:33:29,280
Speaker 1: gets too hot? Like why is it hard to make

633
00:33:29,280 --> 00:33:31,840
Speaker 1: a star from hot gas? Well, hot gas, the particles

634
00:33:31,840 --> 00:33:34,160
Speaker 1: are just flying around too much. You know, gravity is

635
00:33:34,200 --> 00:33:37,000
Speaker 1: not very strong and So if you have a gas

636
00:33:37,120 --> 00:33:39,080
Speaker 1: that's really hot, where the particles are flying around with

637
00:33:39,160 --> 00:33:42,120
Speaker 1: high speed, gravity just doesn't have the power to gather

638
00:33:42,200 --> 00:33:46,280
Speaker 1: them together into a star. Counterintuitive because gravity makes them hot, right,

639
00:33:46,320 --> 00:33:49,080
Speaker 1: but once it's already trapped them in a gravitational well,

640
00:33:49,240 --> 00:33:51,120
Speaker 1: think of it like a scape phlocity. The Earth is

641
00:33:51,160 --> 00:33:53,479
Speaker 1: boiling off molecules right now at the edge of our

642
00:33:53,520 --> 00:33:56,960
Speaker 1: atmosphere because they're too hot for the Earth's gravity to

643
00:33:57,120 --> 00:33:59,440
Speaker 1: contain them. And so it's certainly possible to have a

644
00:33:59,440 --> 00:34:02,560
Speaker 1: whole gas us where there's not enough gravity to contain it,

645
00:34:02,560 --> 00:34:05,680
Speaker 1: where it just disperses, it just keeps flying around instead

646
00:34:05,720 --> 00:34:08,319
Speaker 1: of clumping together to make a dense well at the

647
00:34:08,360 --> 00:34:10,960
Speaker 1: heart of it. But I guess you know, the temperature

648
00:34:11,000 --> 00:34:12,759
Speaker 1: is just one part of it. What if it do

649
00:34:12,760 --> 00:34:15,920
Speaker 1: you have hot gas but really dense or like a

650
00:34:15,960 --> 00:34:17,760
Speaker 1: lot enough of it or a lot of it, wouldn't

651
00:34:17,800 --> 00:34:20,680
Speaker 1: that also sort of create the intensity you need for

652
00:34:21,120 --> 00:34:23,239
Speaker 1: a start to form. Yeah, if you have a seed,

653
00:34:23,280 --> 00:34:25,600
Speaker 1: if you have a dense seed, but how does that form? Right?

654
00:34:25,800 --> 00:34:27,920
Speaker 1: So you need gravity to do that work. The only

655
00:34:27,960 --> 00:34:31,360
Speaker 1: way to get density is to have gravity pull things together.

656
00:34:31,960 --> 00:34:35,160
Speaker 1: So primarily is from having cold clouds of gas. There

657
00:34:35,200 --> 00:34:37,840
Speaker 1: are other rarer waves for it happen. You can have

658
00:34:37,880 --> 00:34:41,359
Speaker 1: supernova shock waves, for example, that compress things and then

659
00:34:41,400 --> 00:34:44,560
Speaker 1: make over densities, but primarily it's just from having clouds

660
00:34:44,560 --> 00:34:48,360
Speaker 1: of cold gas. Interesting, it's like a chill process star formation,

661
00:34:48,880 --> 00:34:51,880
Speaker 1: you know, like a NISA start amount of calm and

662
00:34:52,160 --> 00:34:56,399
Speaker 1: then for things to kind of build up to a start. Right. Yeah,

663
00:34:56,440 --> 00:34:58,560
Speaker 1: you can't rush it, man, It's like the slow food movement.

664
00:34:58,719 --> 00:35:01,319
Speaker 1: You want a hot start, it takes time. Yeah, yeah,

665
00:35:01,600 --> 00:35:05,320
Speaker 1: no fast food galaxies in this universe. It's all organic.

666
00:35:05,719 --> 00:35:11,320
Speaker 1: You can't microwave a star. It's all natural and organic.

667
00:35:11,560 --> 00:35:13,640
Speaker 1: All right. Well, um, you said there's a bit of

668
00:35:13,680 --> 00:35:16,480
Speaker 1: a mystery, right, let in the sense that there are

669
00:35:16,600 --> 00:35:20,640
Speaker 1: more stars sort of quenching or dying or retiring than

670
00:35:20,719 --> 00:35:23,839
Speaker 1: maybe we thought was possible or think is likely. Yeah,

671
00:35:23,840 --> 00:35:26,720
Speaker 1: we sort of can't explain all the quenching that's happening,

672
00:35:26,880 --> 00:35:28,880
Speaker 1: or at least, you know, twenty years ago, when we

673
00:35:28,920 --> 00:35:31,560
Speaker 1: discovered that this was happening, we were very surprised. We

674
00:35:31,640 --> 00:35:35,360
Speaker 1: thought that very gradually galaxies would start to lose the

675
00:35:35,360 --> 00:35:38,320
Speaker 1: ability to form stars, and we've seen this slow drop

676
00:35:38,360 --> 00:35:40,520
Speaker 1: off with a lot of galaxies in the Green Valley

677
00:35:40,560 --> 00:35:43,400
Speaker 1: and a few that are totally quenched. But it happens

678
00:35:43,440 --> 00:35:45,560
Speaker 1: faster than we thought. And so there's been a lot

679
00:35:45,600 --> 00:35:48,120
Speaker 1: of research in the last ten, fifteen, twenty years into

680
00:35:48,400 --> 00:35:50,960
Speaker 1: why galaxies quench, and now we have a few ideas.

681
00:35:50,960 --> 00:35:53,960
Speaker 1: All of course, stimulated by this observation, we dug deep

682
00:35:54,000 --> 00:35:56,759
Speaker 1: into the physics of and thought, how would you quench galaxies?

683
00:35:57,080 --> 00:35:59,560
Speaker 1: What are the processes we might have overlooked that could

684
00:35:59,560 --> 00:36:02,120
Speaker 1: be doing? Is I see? So what do you mean?

685
00:36:02,160 --> 00:36:05,480
Speaker 1: I guess it happens faster than you thought or earlier

686
00:36:05,520 --> 00:36:06,840
Speaker 1: than you thought. Do you know what I mean? Like,

687
00:36:06,840 --> 00:36:09,080
Speaker 1: are you saying that you know the process of retirement

688
00:36:09,200 --> 00:36:11,720
Speaker 1: is faster than you thought, or that it's happening earlier

689
00:36:11,719 --> 00:36:15,640
Speaker 1: than you thought, or that it happens you know, more

690
00:36:15,680 --> 00:36:18,000
Speaker 1: than you thought. All of that right. It definitely happens

691
00:36:18,040 --> 00:36:21,120
Speaker 1: earlier than we thought, because there are more galaxies that

692
00:36:21,160 --> 00:36:24,000
Speaker 1: are quenched that are in that red category than we expected.

693
00:36:24,400 --> 00:36:27,200
Speaker 1: And it also happens faster than we thought because there

694
00:36:27,200 --> 00:36:29,880
Speaker 1: are very few in the Green Valley. There's like two peaks.

695
00:36:29,880 --> 00:36:32,160
Speaker 1: If you look at a distribution of the color of galaxies.

696
00:36:32,360 --> 00:36:34,280
Speaker 1: You don't have a broad spectrum from red to blue.

697
00:36:34,440 --> 00:36:36,480
Speaker 1: If a peak in the blue and a peak in

698
00:36:36,520 --> 00:36:39,239
Speaker 1: the red and almost nothing in between, was suggest that

699
00:36:39,239 --> 00:36:41,960
Speaker 1: galaxies don't live in the green valley very long. When

700
00:36:41,960 --> 00:36:44,640
Speaker 1: they start to quench, they quench quickly and then it's over.

701
00:36:44,840 --> 00:36:47,000
Speaker 1: It's a fast process. You know. There's you can't go

702
00:36:47,080 --> 00:36:49,160
Speaker 1: it for like an independent third party. It's like you're

703
00:36:49,160 --> 00:36:51,000
Speaker 1: either blue or your red. I mean, I guess that's

704
00:36:51,000 --> 00:36:52,960
Speaker 1: good news if you like a quick death. You know,

705
00:36:52,960 --> 00:36:58,799
Speaker 1: it's not a long tortuous struggle against the eventual demise. Man.

706
00:36:58,960 --> 00:37:00,880
Speaker 1: I feel like a lot of the few need today

707
00:37:01,000 --> 00:37:06,239
Speaker 1: is that that to a professor, retirement is dead. They're like,

708
00:37:06,280 --> 00:37:09,799
Speaker 1: wait a minute, wire so many galaxies retiring, Why would

709
00:37:09,800 --> 00:37:12,239
Speaker 1: anyone retire? That's crazy. Yeah, Well, maybe they like it,

710
00:37:12,280 --> 00:37:14,160
Speaker 1: you know, maybe they're tired of making new stars and

711
00:37:14,200 --> 00:37:15,959
Speaker 1: they just want to enjoy the stars that they have

712
00:37:16,400 --> 00:37:18,879
Speaker 1: and hang out for a long time, trillions of years

713
00:37:18,920 --> 00:37:22,439
Speaker 1: until they eventually all fade. Maybe it's a happy retirement. Yeah,

714
00:37:22,480 --> 00:37:24,000
Speaker 1: there you go. You don't have to call it death.

715
00:37:25,080 --> 00:37:29,720
Speaker 1: It could be their their new life, their second life.

716
00:37:29,880 --> 00:37:31,600
Speaker 1: So that was the mystery. I guess and you said

717
00:37:31,640 --> 00:37:34,279
Speaker 1: that physicists have looked into this, and so they have

718
00:37:34,400 --> 00:37:37,320
Speaker 1: theories I guess about what's making all of these galaxies

719
00:37:37,320 --> 00:37:39,680
Speaker 1: retire so quickly. They have theories. None of them are

720
00:37:39,719 --> 00:37:42,800
Speaker 1: really perfect or comprehensive, but they have a few cool ideas.

721
00:37:42,960 --> 00:37:45,440
Speaker 1: One is related actually to the black hole at the

722
00:37:45,440 --> 00:37:48,040
Speaker 1: heart of the galaxies. And it's not the black hole

723
00:37:48,120 --> 00:37:50,759
Speaker 1: is gobbling up stars all that stars are falling into it,

724
00:37:51,000 --> 00:37:53,960
Speaker 1: but black holes actually admit a lot of radiation. The

725
00:37:54,000 --> 00:37:56,959
Speaker 1: black hole itself is not hot. Gas in the dust

726
00:37:56,960 --> 00:37:59,640
Speaker 1: that's swirling around the black hole before it falls in

727
00:38:00,040 --> 00:38:03,040
Speaker 1: gets really hot and emits a lot of radiation, and

728
00:38:03,080 --> 00:38:05,480
Speaker 1: so that blows out a lot of the gas and dust.

729
00:38:05,760 --> 00:38:08,560
Speaker 1: Once we talked about like how supermassive black holes form,

730
00:38:08,880 --> 00:38:11,240
Speaker 1: and there's a maximum rate at which they can grow

731
00:38:11,560 --> 00:38:13,800
Speaker 1: because the bigger they get, the more they push away

732
00:38:13,880 --> 00:38:16,800
Speaker 1: the gas that's feeding them. And so this could also

733
00:38:16,840 --> 00:38:20,240
Speaker 1: be spewing out radiation into the galaxy, which heats up

734
00:38:20,280 --> 00:38:22,600
Speaker 1: a lot of the gas in the galaxy or also

735
00:38:22,640 --> 00:38:25,239
Speaker 1: helps blow it out of the galaxy, and so that

736
00:38:25,280 --> 00:38:28,600
Speaker 1: can stifle star formation. I see you're saying, like you know,

737
00:38:28,680 --> 00:38:32,640
Speaker 1: because star formation depends on very chill, calm conditions. Anything

738
00:38:32,680 --> 00:38:35,400
Speaker 1: that kind of excites the galaxy is not good for

739
00:38:35,480 --> 00:38:38,160
Speaker 1: star formation. So one idea is that maybe it's the

740
00:38:38,320 --> 00:38:40,600
Speaker 1: black hole in the middle of galaxies that's I guess

741
00:38:40,600 --> 00:38:43,520
Speaker 1: agitating everything. Yeah, and we see that these black holes

742
00:38:43,760 --> 00:38:46,160
Speaker 1: grow at the same rate of galaxies is like a

743
00:38:46,560 --> 00:38:49,160
Speaker 1: ratio of the black hole mass to the galaxy mass,

744
00:38:49,200 --> 00:38:52,320
Speaker 1: which seems roughly constant. And so that might help explain

745
00:38:52,360 --> 00:38:54,879
Speaker 1: it because as these galaxies get big and get old,

746
00:38:55,239 --> 00:38:57,880
Speaker 1: the black hole gets big and powerful and not just

747
00:38:57,960 --> 00:39:00,680
Speaker 1: heats up the gas, but also helps prevent more gas

748
00:39:00,719 --> 00:39:04,000
Speaker 1: from falling into the galaxy from these filaments from the

749
00:39:04,000 --> 00:39:08,080
Speaker 1: intergalactic medium or the circum galactic medium. All right, but

750
00:39:08,320 --> 00:39:10,360
Speaker 1: so that's one idea, but it's not perfect. It's not

751
00:39:10,400 --> 00:39:12,120
Speaker 1: perfect because you know, the black hole is at the

752
00:39:12,160 --> 00:39:14,560
Speaker 1: center and they don't really understand how it could like

753
00:39:14,640 --> 00:39:17,439
Speaker 1: heat up the entire galaxy. You should still see star

754
00:39:17,520 --> 00:39:20,120
Speaker 1: formation sort of at the edges in that case. So

755
00:39:20,160 --> 00:39:23,560
Speaker 1: we can't explain everything. Okay, So then what's another possible

756
00:39:23,719 --> 00:39:27,560
Speaker 1: star retirer or another possibility is that stars themselves are

757
00:39:27,640 --> 00:39:31,640
Speaker 1: killing the galaxy. Remember that stars also generate radiation. Our

758
00:39:31,719 --> 00:39:34,719
Speaker 1: Sun doesn't just send out light. It sends out protons

759
00:39:34,760 --> 00:39:37,360
Speaker 1: and electrons and all sorts of stuff the solar wind.

760
00:39:37,880 --> 00:39:40,360
Speaker 1: And so if you have a lot of these stellar winds,

761
00:39:40,760 --> 00:39:43,399
Speaker 1: these particles, they can be blowing the gas out as

762
00:39:43,400 --> 00:39:46,440
Speaker 1: well or heating it up. It's sort of the same process.

763
00:39:46,520 --> 00:39:49,560
Speaker 1: This happens at the galactic center from the black hole,

764
00:39:49,840 --> 00:39:52,640
Speaker 1: but instead it's happening everywhere all at once. So in

765
00:39:52,680 --> 00:39:55,080
Speaker 1: some senses, it's a better candidate for what might be

766
00:39:55,080 --> 00:39:58,680
Speaker 1: stopping star formation because it's spread out across the whole galaxy.

767
00:39:59,000 --> 00:40:01,480
Speaker 1: N See, it's sort of like stars form, but then

768
00:40:01,520 --> 00:40:05,399
Speaker 1: they kind of spoil star formation for the area around them, right,

769
00:40:05,640 --> 00:40:07,640
Speaker 1: because it like it forms a star, and but then

770
00:40:07,640 --> 00:40:09,839
Speaker 1: it starts to heat up this gas around and so

771
00:40:10,160 --> 00:40:13,120
Speaker 1: nobody can make new stars. It's really nimbism, you know.

772
00:40:13,120 --> 00:40:15,400
Speaker 1: It's all these old professors. They've got these nice houses

773
00:40:15,400 --> 00:40:17,120
Speaker 1: they bought in the sixties, and they don't want anybody

774
00:40:17,120 --> 00:40:22,920
Speaker 1: building apartments in their backyard. Yeah, or like you know,

775
00:40:23,080 --> 00:40:28,799
Speaker 1: like you know, the old professors taken up office face exactly,

776
00:40:28,960 --> 00:40:31,440
Speaker 1: I got to make room for those young bloods, alright.

777
00:40:31,480 --> 00:40:33,520
Speaker 1: So and but that this one is also maybe not

778
00:40:33,600 --> 00:40:36,360
Speaker 1: a perfect idea or cost Yeah, because remember that the

779
00:40:36,360 --> 00:40:39,360
Speaker 1: galaxy is surrounded by gas, and that gas should be

780
00:40:39,360 --> 00:40:41,880
Speaker 1: falling in the dark matter halo should be pulling that

781
00:40:42,040 --> 00:40:45,600
Speaker 1: gas in and supplying us with fresh cold gas that's

782
00:40:45,640 --> 00:40:48,640
Speaker 1: been out there between galaxies that hasn't been heated up

783
00:40:48,920 --> 00:40:51,759
Speaker 1: from the stellar winds. So another area of research is

784
00:40:51,840 --> 00:40:56,040
Speaker 1: understanding why that might stop happening. And one suggestion there

785
00:40:56,239 --> 00:40:58,360
Speaker 1: is that the dark matter halo, the thing that forms

786
00:40:58,360 --> 00:41:02,279
Speaker 1: our galaxy and shapes it and provides the gravitational well

787
00:41:02,400 --> 00:41:04,680
Speaker 1: to suck in this new gas that might get a

788
00:41:04,719 --> 00:41:08,239
Speaker 1: little too big. If that gets really big, then it's

789
00:41:08,239 --> 00:41:11,279
Speaker 1: gravitational power is really strong. And then what happens when

790
00:41:11,280 --> 00:41:14,279
Speaker 1: the gas falls in from outside the galaxy into the

791
00:41:14,280 --> 00:41:16,839
Speaker 1: galaxy is that it gets heated up. This is called

792
00:41:16,920 --> 00:41:19,239
Speaker 1: shock heating. If this is like a gradient in the

793
00:41:19,320 --> 00:41:22,480
Speaker 1: density outside the galaxy, then when this gas falls in,

794
00:41:22,520 --> 00:41:24,840
Speaker 1: it basically collides with the other gas and then it

795
00:41:24,840 --> 00:41:27,480
Speaker 1: gets too hot, and so you get hot gas falling

796
00:41:27,520 --> 00:41:30,000
Speaker 1: in instead of cold gas, and then you can't use

797
00:41:30,080 --> 00:41:32,960
Speaker 1: that to make new stars interesting. But but what do

798
00:41:33,000 --> 00:41:35,160
Speaker 1: you mean the dark matter halo gets too big, like

799
00:41:36,000 --> 00:41:39,319
Speaker 1: dark matter is growing in galaxies. The dark matter halo

800
00:41:39,440 --> 00:41:42,200
Speaker 1: is definitely growing because you know, we have these filaments

801
00:41:42,200 --> 00:41:44,879
Speaker 1: and it's sucking in not just gas but also dark

802
00:41:44,920 --> 00:41:47,239
Speaker 1: matter gravity in the universe. Remember, its goal is to

803
00:41:47,280 --> 00:41:50,400
Speaker 1: gather everything together. So the reason you have these halos

804
00:41:50,760 --> 00:41:53,160
Speaker 1: and then these filaments is that the filaments are feeding

805
00:41:53,239 --> 00:41:56,120
Speaker 1: the halos, and not just baryonic matter, not just normal

806
00:41:56,160 --> 00:41:58,920
Speaker 1: matter like gas and dust, but also dark matter is

807
00:41:58,960 --> 00:42:02,560
Speaker 1: flowing along these filaments into our halo. So our halo

808
00:42:02,640 --> 00:42:04,759
Speaker 1: is getting bigger and bigger. Oh I see. So as

809
00:42:04,800 --> 00:42:07,400
Speaker 1: the galaxies get older, they pull in more of the

810
00:42:07,480 --> 00:42:10,759
Speaker 1: stuff around them, They get bigger and heavier, which makes

811
00:42:10,760 --> 00:42:15,600
Speaker 1: them more gravitationally powerful, which sucks in the gas maybe

812
00:42:15,600 --> 00:42:18,040
Speaker 1: too fast, and so when it sucks it in, it's

813
00:42:18,080 --> 00:42:20,600
Speaker 1: too hot and it can form anymore stars. And all

814
00:42:20,680 --> 00:42:22,480
Speaker 1: this just comes together to give you a picture of

815
00:42:22,560 --> 00:42:26,200
Speaker 1: star formation and galaxies as sort of fragile and special,

816
00:42:26,520 --> 00:42:28,759
Speaker 1: like you need these special conditions. Things have to be

817
00:42:28,880 --> 00:42:31,640
Speaker 1: just right, and it's not that hard to perturb it

818
00:42:31,680 --> 00:42:33,879
Speaker 1: and to make it to the galaxies while they're still

819
00:42:33,880 --> 00:42:36,840
Speaker 1: big swirling blobs of stuff, they're no longer have the

820
00:42:36,880 --> 00:42:40,279
Speaker 1: conditions to make these stars and you know, without stars, Wow,

821
00:42:40,280 --> 00:42:43,080
Speaker 1: the universe just wouldn't be the same place. Makes you

822
00:42:43,120 --> 00:42:44,959
Speaker 1: wonder if, like, if the universe has been a little

823
00:42:44,960 --> 00:42:47,319
Speaker 1: bit different, would we have not gotten stars at all,

824
00:42:47,680 --> 00:42:51,719
Speaker 1: just like big swirls of hot gas that never formed stars. Yeah,

825
00:42:51,719 --> 00:42:54,360
Speaker 1: it would be a much darker universe, right without stars,

826
00:42:54,560 --> 00:42:57,920
Speaker 1: but you couldn't see anything exactly. We certainly wouldn't be here, right,

827
00:42:58,000 --> 00:43:00,920
Speaker 1: You could have a literally dead universe that the capacity

828
00:43:00,960 --> 00:43:03,520
Speaker 1: to form life if it had been a little hotter,

829
00:43:03,760 --> 00:43:05,600
Speaker 1: if all the gas in the universe have been too

830
00:43:05,600 --> 00:43:08,040
Speaker 1: hot to form stars in the very beginning, well you

831
00:43:08,040 --> 00:43:11,320
Speaker 1: would still have I guess quasars, right, like black holes

832
00:43:11,560 --> 00:43:14,239
Speaker 1: maybe shining because of the gas swirling around them. You

833
00:43:14,360 --> 00:43:17,000
Speaker 1: still have some bright spots in the universe, right, Oh yeah,

834
00:43:17,000 --> 00:43:19,160
Speaker 1: absolutely quasars, You're right, and there were some of the

835
00:43:19,200 --> 00:43:21,960
Speaker 1: brightest things in the universe. I wonder if life could

836
00:43:21,960 --> 00:43:24,480
Speaker 1: form in the vicinity of a quaisar. Yeah, that would

837
00:43:24,480 --> 00:43:26,320
Speaker 1: be pretty cool, right, I mean to to that, to

838
00:43:26,440 --> 00:43:30,040
Speaker 1: that civilization, it would be indistinguishable, right, that would be

839
00:43:30,040 --> 00:43:32,320
Speaker 1: their son, that would be their son. Yeah, And in

840
00:43:32,480 --> 00:43:35,120
Speaker 1: podcasts around that quasar, they would wonder, you know, our

841
00:43:35,200 --> 00:43:38,000
Speaker 1: quays are still growing. They would wonder why quasars are

842
00:43:38,040 --> 00:43:41,080
Speaker 1: no longer forming, because you know, also quasars formed in

843
00:43:41,120 --> 00:43:43,480
Speaker 1: the early universe, and we're not really making quasars at

844
00:43:43,480 --> 00:43:46,640
Speaker 1: the same rate as we used to. That's the next episode.

845
00:43:46,640 --> 00:43:50,040
Speaker 1: I guess how to quasars retire? Who's killing off the quasar?

846
00:43:51,120 --> 00:43:55,000
Speaker 1: I'm just trying to tap into the paranormal true crime podcasts,

847
00:43:55,040 --> 00:43:57,479
Speaker 1: which seemed to be so popular. I see, I see,

848
00:43:57,480 --> 00:44:03,520
Speaker 1: I see, you're going for um murder. Is Bigfoot killing galaxies?

849
00:44:04,480 --> 00:44:06,759
Speaker 1: Next time? On Daniel and Jorge? That's right, although we

850
00:44:06,800 --> 00:44:09,960
Speaker 1: still want the science category. Amazically Bigfoot podcasts are in

851
00:44:09,960 --> 00:44:13,400
Speaker 1: the science category. Don't get me started on that. Oh really? Wow?

852
00:44:13,600 --> 00:44:16,600
Speaker 1: Well not maybe not the natural sciences category. Oh yes,

853
00:44:16,719 --> 00:44:19,440
Speaker 1: in the natural sciences. Well, I guess who killed Bigfoot

854
00:44:19,480 --> 00:44:23,640
Speaker 1: would be another topic. Why is Bigfoot retiring that his

855
00:44:23,760 --> 00:44:27,360
Speaker 1: foot or her foot stop growing? Maybe he stepped on

856
00:44:27,360 --> 00:44:30,160
Speaker 1: a galaxy and got quenched. All right, Well, so those

857
00:44:30,200 --> 00:44:33,839
Speaker 1: are three reasons why a galaxy might stop making new stars?

858
00:44:33,920 --> 00:44:35,799
Speaker 1: Is there are there any other reasons? There are lots

859
00:44:35,800 --> 00:44:38,120
Speaker 1: of other theories out there. Some of them involve like

860
00:44:38,160 --> 00:44:41,520
Speaker 1: how galaxies tug on each other. Like, we've noticed that

861
00:44:41,680 --> 00:44:44,759
Speaker 1: sometimes galaxies that are more by themselves that aren't part

862
00:44:44,760 --> 00:44:47,960
Speaker 1: of a cluster tend to get quenched less often. One

863
00:44:48,040 --> 00:44:51,520
Speaker 1: hypothesis is that galaxies are like harassing each other, that

864
00:44:51,719 --> 00:44:55,759
Speaker 1: gravity from other nearby galaxies might be preventing gas from

865
00:44:55,840 --> 00:45:00,000
Speaker 1: falling into those galaxies to help spurn new star formation.

866
00:45:00,200 --> 00:45:01,719
Speaker 1: So if you're in the middle of a cluster rather

867
00:45:01,719 --> 00:45:04,080
Speaker 1: than by yourselves, might be that your friends and the

868
00:45:04,080 --> 00:45:07,600
Speaker 1: cluster are interfering with a gas infall you need to

869
00:45:07,640 --> 00:45:11,600
Speaker 1: make those new stars. M wouldn't other galaxies will help

870
00:45:11,680 --> 00:45:14,359
Speaker 1: you in a way slow down or cool off your

871
00:45:14,400 --> 00:45:16,920
Speaker 1: own gas, makeing it better to make stars. Yeah, they

872
00:45:16,920 --> 00:45:19,160
Speaker 1: do slow it down, but they might slow down to

873
00:45:19,200 --> 00:45:21,640
Speaker 1: the point where it doesn't fall into your galaxy anymore.

874
00:45:22,000 --> 00:45:24,720
Speaker 1: So you still need that gas. It's a really fine

875
00:45:24,719 --> 00:45:26,759
Speaker 1: balance that you need the gas to fall in but

876
00:45:26,840 --> 00:45:30,160
Speaker 1: not too fast. You need it to be um like

877
00:45:30,200 --> 00:45:32,840
Speaker 1: in the Goldilocks zone kind of. Yeah, you need a

878
00:45:32,960 --> 00:45:36,719
Speaker 1: very slow delivery of frozen gas. All right, Well, I

879
00:45:36,719 --> 00:45:39,279
Speaker 1: guess that's the mystery. Although I wouldn't you just think

880
00:45:39,320 --> 00:45:41,719
Speaker 1: that you know a galaxy is born, it has owned

881
00:45:41,719 --> 00:45:43,840
Speaker 1: amount of a cold gas and at some point it

882
00:45:43,920 --> 00:45:46,319
Speaker 1: runs out, and so the whole thing just kind of

883
00:45:46,560 --> 00:45:49,320
Speaker 1: and all at the same time. Like, wouldn't that also

884
00:45:49,360 --> 00:45:52,640
Speaker 1: be an explanation why it seems to be so binary,

885
00:45:52,760 --> 00:45:55,759
Speaker 1: so red or blue, like it just runs all out

886
00:45:55,760 --> 00:45:58,080
Speaker 1: of gas at the same time, because all of it

887
00:45:58,120 --> 00:46:00,640
Speaker 1: was formed at the same time. Yeah, it's an question

888
00:46:00,840 --> 00:46:04,320
Speaker 1: why it's a surprise that galaxies quench all at once.

889
00:46:04,760 --> 00:46:08,120
Speaker 1: You're imagining that they start with some supply of gas,

890
00:46:08,520 --> 00:46:11,040
Speaker 1: and then the star forming that uses that gas is

891
00:46:11,080 --> 00:46:14,160
Speaker 1: like used up all at once, all over the galaxy.

892
00:46:14,640 --> 00:46:17,279
Speaker 1: But remember that it's not really about having the raw

893
00:46:17,360 --> 00:46:20,640
Speaker 1: materials the gas to make stars. You could keep making

894
00:46:20,719 --> 00:46:23,520
Speaker 1: stars for zillions of years with the gas supply that

895
00:46:23,560 --> 00:46:26,000
Speaker 1: we have. Stars burn and die, and you could just

896
00:46:26,080 --> 00:46:29,000
Speaker 1: keep making new stars for a long time. The issue

897
00:46:29,480 --> 00:46:33,960
Speaker 1: isn't the supply, it's the conditions to make new stars. Remember,

898
00:46:34,000 --> 00:46:37,960
Speaker 1: you need cold conditions. So it's a surprise if something

899
00:46:38,480 --> 00:46:42,040
Speaker 1: is spoiling those conditions and doing it quickly and in

900
00:46:42,080 --> 00:46:46,320
Speaker 1: a sort of coordinated banner across the galaxy all at once.

901
00:46:46,760 --> 00:46:48,719
Speaker 1: That's not what you expect to have from just the

902
00:46:48,800 --> 00:46:53,440
Speaker 1: sort of random distribution of conditions that you expect in galaxies.

903
00:46:54,680 --> 00:46:57,359
Speaker 1: You see, it doesn't match a random distribution, is It's

904
00:46:57,400 --> 00:46:59,879
Speaker 1: kind of the mystery. All right? Well, um, I hope

905
00:47:00,080 --> 00:47:03,279
Speaker 1: find a culprit, Daniel, you know, maybe before it kills

906
00:47:03,280 --> 00:47:05,880
Speaker 1: our galaxy or no, wait, our galaxes already dead. Well

907
00:47:05,920 --> 00:47:08,319
Speaker 1: I thought you were pro galaxy retirement anyway, so I

908
00:47:08,320 --> 00:47:10,799
Speaker 1: thought you'd want to find the culprit and then encourage it, like,

909
00:47:10,840 --> 00:47:13,359
Speaker 1: hey man, you let all these galaxies off the hook.

910
00:47:13,440 --> 00:47:16,520
Speaker 1: They've done enough. I have pro retirement in any situation.

911
00:47:18,000 --> 00:47:20,279
Speaker 1: All Right, you teenagers out there, Jorge suggesting that you

912
00:47:20,360 --> 00:47:26,239
Speaker 1: retire tonight, Yeah, if you can, you know, go for it.

913
00:47:26,480 --> 00:47:28,960
Speaker 1: You know, I feel like I retired in my early twenties,

914
00:47:29,080 --> 00:47:32,160
Speaker 1: so I definitely recommend you retired and then started three

915
00:47:32,239 --> 00:47:36,560
Speaker 1: or four new careers. Yeah. I've retired about three times.

916
00:47:37,000 --> 00:47:39,560
Speaker 1: That's how pro retirement I am, Daniel, exactly. So I

917
00:47:39,560 --> 00:47:41,640
Speaker 1: guess we shouldn't think of these galaxies is quenched. We

918
00:47:41,719 --> 00:47:44,439
Speaker 1: should think of them as beginning their next adventure. Yeah,

919
00:47:44,480 --> 00:47:46,440
Speaker 1: there you go, and we hope you also find your

920
00:47:46,480 --> 00:47:49,400
Speaker 1: next adventure pretty soon in the near future, hopefully in

921
00:47:49,480 --> 00:47:52,399
Speaker 1: this galaxy before it retires. And remember that we are

922
00:47:52,440 --> 00:47:55,640
Speaker 1: still learning about the process of galaxy formation and galaxy

923
00:47:55,719 --> 00:47:59,120
Speaker 1: quenching and galaxy retirement, and hopefully we will live long

924
00:47:59,200 --> 00:48:01,799
Speaker 1: enough to learn much much more. Yeah, and I guess

925
00:48:01,800 --> 00:48:03,960
Speaker 1: the main lesson is that the universe is still a

926
00:48:04,040 --> 00:48:08,000
Speaker 1: work in progress. It's changing, it's growing, it's changing its

927
00:48:08,040 --> 00:48:11,560
Speaker 1: color and showing its age. It's getting redder and redder. Well,

928
00:48:11,600 --> 00:48:13,799
Speaker 1: we hope you enjoyed that. Thanks for joining us, See

929
00:48:13,800 --> 00:48:24,120
Speaker 1: you next time. Thanks for listening, and remember that Daniel

930
00:48:24,160 --> 00:48:26,680
Speaker 1: and Jorge Explain the Universe is a production of I

931
00:48:26,880 --> 00:48:30,319
Speaker 1: Heart Radio. For More podcast. For my heart Radio, visit

932
00:48:30,360 --> 00:48:33,840
Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you

933
00:48:33,960 --> 00:48:41,160
Speaker 1: listen to your favorite shows. Yea