What are globular clusters?

Published Mar 2, 2021, 6:00 AM

Daniel and guest host Katie Goldin explore the mysteries of these weird, ancient blobs of stars.

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Hey, Katie, do you have science words that you especially like?

Yeah?

I really like apoptosis. It makes me think of popcorn.

That does make me want to have a snack. Well, I like the word fundamental. It sounds so.

Important, it's got fun in.

It, it does. So what science words don't you like?

Coagulate?

I was afraid you're gonna say moist. Coagulate's pretty gross. Also, I'm not such a fan of the word hadron.

Oh really, No.

The problem is a lot of people end up with a little typo that swaps a couple letters, and you end up with something very not safe for work.

Yeah, that gives the lard hadron collider a whole different connotation.

Hi, I'm Daniel, I'm a particle. Physicist and I definitely am Colliding Hadrons at the LHC.

And I am Katie Golden. I'm stepping in for Jorge this week, and I am the host of Creature Feature. I'm a science pod cast interested in evolutionary biology, human psychology, and hate also physics.

And welcome to the podcast. Daniel and Jorge explain the Universe, in which we take you on a mental journey to understand everything about the universe, from the tiniest things between your toes to the things you see in the night sky to the vast weird, crazy bonker stuff going out in the depths of space. We take all of it, roll it up and try to make sure that you understand it.

Like a cosmic burrito.

How much hot sauce you want is up to you. And we love to talk about stuff that we see in the night sky, but we also love to talk about stuff you might not have even heard of. When you look up in the sky, you see stars, and if you have a nice telescope, you can even see further and maybe see those smudges that are galaxies. But there's a lot of other stuff out there in the universe that we are not familiar with that most people don't even know exists.

Okay, So if I'm looking at the night sky, I see a bunch of stars. Sometimes I see like, like you said, it looks like someone spilled a bunch of sugar up there, and it's a galaxy. But what can I possibly be missing? I mean other than yeah, I guess I can't see them in detail with a telescope. But what's up there? Like you mean giant alien eyeballs?

Well, there's a lot of stuff out there, and basically, every time we turn on a new telescope or a new kind of device for listening to the cosmos, we find something new. And every time we peer deeper and deeper into the sky, we see stuff that we didn't expect. On the podcast today, we'll be talking about a weird thing that's in the sky that astronomers have known about for hundreds of years but most people aren't aware of.

All Right, well, what's this big secret? What have astronomers been keeping from us?

Well, unfortunately, it's got a really strange and kind of an ugly name.

Uh.

Oh, it's not coagulate, is it?

Stars don't coagulate? I guess if a galaxy cuts itself, right, a bunch of like stars could rush in to fill in the gap planetary platelets.

No.

Today on the program, we'll be asking the question, what are globular clusters? Eww doesn't sound like something you want to order on the menu, does it.

No? No, it sounds like the worst kids cereal ever, Like, be sure to get globios for your globular clusters.

I know, I imagine some like scoop of some very viscous kind of stuff. It's like jello mixed with gravy or something.

Oh man, I don't I have a texture thing when it comes to food, Like I don't like cottage cheese or other like things little chunks suspended within gow. So I don't know about this globular clusters thing. This does not sound good.

Well, fortunately it was not designed as a menu item. It's an astrophysical object. It's something out there in our universe that might teach you something about how the galaxy was formed and how old the universe is and weird new kinds of stars and so it's an opportunity to learn something. And fortunately we don't actually have to taste it.

That's good, that's good, all right, I'm still with you then, But if you try to give me a spoon on one of these globular clusters, I am check please. So we ask what people think globular clusters are, and this is what people had to say.

I don't know what a globular cluster is. I think it might be something fond and out of space, but I don't actually know.

I'm not sure entirely, but I think it's just some type of grouping of stars. Assuming it's a term from cosmology. A cluster is a collection enough stars, and globular means that it's round, like a globe, and the eule as in molecule or module, suggests that it's small, so it's a small round a bunch of stars.

This one is like a gathering of stars, spherical. It's not a galaxy.

It can be within a galaxy, but it may look like a galaxy, like a spherical galaxy. I've heard the phrase globular cluster, not one hundred percent sure what it means. I thought that it had something to do with a group of stars maybe that are clustered together in like a spherical shape.

This is a gigantic group of stars that sit outside and I think maybe even orbit the galaxies.

This has something to do with a group of stars, maybe that they all for from the same nebula or.

Other event.

Thanks to everybody who volunteered to speculate baselessly without getting to do any research or googling. If you'd like to participate for a future episode, please write to me two questions at Danielanjorge dot com.

I think it's interesting, so most of the answers more along the same lines, like this is probably a big cluster of stars or some kind of space junk.

Some kind of space junk. But there's no clue in there that it's a cluster of stars, right, it could have been a cluster of anything, you know, jello or gravy or breakfast cereal or whatever.

I think when people think about space, you think of it mostly stars. Right, you look out into space. What do you see? You see stars? All the other stuff that is out there is either hard to see or is it really perceivable.

Yeah, but you hear some people speculating like maybe a cluster of galaxies or a cluster of galaxy clusters or something like that, because there's this fascinating sort of hierarchy of structure out there. In space, right, It's not like there are just stars everywhere. Things are sort of grouped together into galaxies, and those galaxies are grouped together into clusters of galaxies, and so this really fascinating sort of hierarchy of structures getting bigger and bigger and bigger. And so I guess the question then is, you know, like, what are globular clusters a cluster of.

Yes, what kind of pyramid scheme is a globular cluster? Who's the downstream and who's the upstream?

Who's really making money off globular clusters? Right? Who's behind big globular.

Taking globular clusters to the moon.

So the answer is that globular clusters are clusters of stars, And to me, the fascinating thing is that there's something in between, sort of like our solar system and the galaxy. You think about like our cosmic address. We're here on Earth where zooming around our star, and then we think that our star is just like one of many stars of hundreds of billions of stars in the galaxy. Right, But it turns out that there's an intermediate step there. It's not just solar system and then galaxy. You could have organizations of solar systems.

So when you zoom out, like when you see these videos of here, you are on planet Earth. You're a tiny, insignificant flea like creature on this huge planet. Then you zoom out to Solar system and usually goes right from Solar system to galaxy. But no, there's an extra step.

You're saying, there's an extra step. Yeah, some stars, some special stars, group together into these big clusters of stars called globular clusters. Now, not every star is in one of these things. It's not like you know, another layer in this hierarchy. It's sort of like a special clumping. Like most stars are just sort of like out they're on their own, sort of like out in the middle of the countryside by themselves. But it turns out that there are these like urban areas where stars clump together really densely and make these things called globular clusters, and they're like a fascinating relic of the ancient formation of the galaxy and can tell us a lot about how things work out there.

So it's like you've got a bowl of granola and yet you have your little oatmeal pieces in there. But then you have the big clusters of oatmeal too.

Those are the best ones.

Those are the best ones. Those are nice. Yeah, I always fish those out first, and then I'm left with just sort of a bowl of sugary oatmeal, and that's not great. But so that whole bowl is like the galaxy. But within that bowl you have the globular clusters of the nice, crunchy granolas.

Yeah, exactly. The stars are not evenly distributed through the galaxy. I mean, the overall pattern is that there's more stars in the center of the galaxy where the gravity stronger, and then it sort of peters out along the galactic disc. But inside there it's not smooth. There are these clumps where you get these big collections of stars. And we're not talking like, you know, five ten stars. We're talking like a few hundreds of thousands of stars. It's a big deal.

Sounds like when they were making the galaxy, they just didn't stir enough. That's what I learned about. Like when I'm trying to make polenta, you know, it gets clumpy. You just didn't stir enough.

Katie's globular Polinda. That's not the foundation for your next food truck run. And so these things have like a few hundred thousand stars in them. But they're not actually that big, right, They're only like ten to sometimes like three hundred light years wide.

Okay, you say that's not that big. However, how long would it take me to drive from one end to the other of three hundred light years?

Yeah, it would take you a while. I mean, even in your light speed polenta powered vehicle, it would take you three hundred years to go across three hundred light years obviously, and in a much slower, more reasonable ship it would take much much longer. But the reason I say that it's not that big is that there are so many stars in there, So what you end up with is stars in a very unusually dense collection, Like in our part of the galaxy, in our neighborhood, there aren't that many stars, like the nearest stars more than four light years away, right.

I mean, it seems like there would be conflict with stars being that close together, right, because I know every body in the universe has some kind of gravitational pull, and stars are so big they seem like they would be acting on each other, So it's odd that you would have them so close together.

Yeah, and that's exactly what makes them fascinating because in these clusters we get to see stars doing something they don't normally do, which is like dance around each other and tug on each other and form new, weird kinds of stars. And we're going to dig into all that crazy stuff that's happening inside the globular clusters in a minute. But here's some numbers for you, Like the density of stars in our neighborhood, like around where we live in the Galley, is like one star per three hundred cubic light years, So that's a pretty big area just to get one star. But inside one of these globular clusters, there's like two stars per cubic light year, so it's like six hundred times denser than it is in our neighborhood. It's like going from the middle of nowhere to Manhattan.

You're really packed in there, like stardines.

Yeah, they really are. Imagine what it would be like to live around a star in a globular cluster. You would have so many other like bright stars in the sky at night, the night itself might be a lot brighter than it is here.

Yeah, it seems like it'd be as bright as daylight. You just have too many suns going on.

Yeah, if you're near the center one of these things, I mean, the globular cluster itself is like twenty five thousand times brighter than the sun. These things are really bright. Some of them are up to like fifty times brighter than even that. You'd be in the middle of like a lot of light bulbs all the time. It would be a pretty crazy experience.

Well, I need to get get some more high tech sunglasses. It seems like to be able to live here. It's some of that those polarized shades. But before I do that, why don't we take a quick break and I will return with all new sunglasses.

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All Right, I've got my super polarized super extra tiglare globular cluster sunglasses on it. I can't see a thing indoors, but I think it'll help me see within the globular clusters. So what's going on around me?

Yes, So these globular clusters, you have this big collection of stars all packed into one spot. And one of the amazing things is that there aren't actually that many of these, Like the galaxy has hundreds of billions of stars, but they're only about one hundred and fifty, maybe up to two hundred of these globular clusters.

Why are they so rare?

We don't really understand, and we can talk in a minute about how they form, but one clue is that they're also not always contained within the galactic disk. Like if you just look at the galaxy sort of from outside, which we can't do but we can look at other galaxies, of course, you see that it's mostly a flat swirl, and that's because of how the galaxy formed.

Right.

The galaxy form from a huge collection of gas and dust which collapsed into stars, and then gravity took over and tried to pull all those stars together, and that's why you have a galaxy, but it's much harder for gravity to pull along the galactic plane because that's how the galaxy is spinning. That's spinning keeps things from falling in only along that plane. Perpendicular to that plane, it can squish it flat like a pancake.

Is it sort of like when you have a bicycle wheel, You have some torque there, so you have that kind of like inward energy of the galaxy spinning, so it's easier for it to be flat and spinning inward than it is to spin another direction.

Yeah, exactly, if you spin a bicycle wheel, then it's harder for things to sort of fall in towards the center. Or if you think, for example, about like a merry go round with ping pong balls on it, right, you spin that thing, the ping pong balls are all going to fly out, but they're going to fly out along that plane. So that's what we call rotation supported the rotation of the galaxies keeping things from falling inwards, but again only along that plane. It's nothing that prevents the collapse perpendicular to that plane, which is what makes it flat like.

Disc Next time I go on a merry go round, I'm bringing a bunch of ping pong balls with me. This is probably why I'm banned for Most Merry Go Round.

Maybe also because you try to eat polenta and then you end up throwing up globular chunks of polenta from the America.

Oh man, When I was a kid, I was a throw upper kid, and I had some moments. I had my moments, especially on the teacups.

All right, well, we don't want to revisit that with too much to tail. But the interesting thing about these globular clusters is that they don't tend to be along this galactic disc. Like if you looked at a diagram of where they are, there's some of them that are in the disc, but they're also sort of just spherically distributed around the galaxy. It's almost like they come from a time when the galaxy was a big puffy spear before it collapsed.

Right, And I'm looking at this image, and what it looks like to me is like a side view of like a fried egg, and then above it, like scattered around it our little little yell dots like you just spilled a bunch of salt around. I man, I keep coming back to food on this globular cluster episode, don't I we gotta stop recording these at lunch.

Who ever thought globular clusters would make you hungry?

I gotta bring a positive spin to it. So they're falling outside of that disc. You're saying that maybe these had formed back when the galaxy was sort of this big puppy cloud, and even as it flattened down to the disk, they didn't come with the rest of the game.

Yeah, precisely. And there's a bigger topic here of the galaxies halo. Remember that galaxies are not mostly stars. Most of what's in the galaxies actually dark matter. And if you look at where the dark matter is in a galaxy, it doesn't collapse the same way that normal matter does. It tends to spin. And so there's this big spherical halo of dark matter around the galaxy and that's the original thing that's sort of like clustered together the gas and the dust that made our galaxy. And so these globular clusters, they're sort of in this larger galactic halo, but they haven't collapsed down into this disc. And we don't know exactly why it could be that they didn't form with the original galaxy, but are like their own little mini galaxies that were then captured later and that's why they're orbiting around. Or it could be that they formed with the rest of the galaxy but then didn't collapse as well as the gas and dust because they don't collide with each other as much as the gas clouds do, so they avoided like losing all that angular momentum and they can keep spinning around out there in crazy orbits. Or maybe they just prefer to hang out out in the dark matter Halo.

Dark matter Halo is a really good metal band name. I've got to say. Yeah, so that's interesting. We can't see dark matter, but it is there, and so it's like this halo around the glac disk. And suspended in that halo are these little dots and those are each a globular cluster.

Yeah, exactly, And some of them happen to fall within the galactic disk, but most of them do not. You know, the closest one to us is about sixteen thousand light years away. It's called the Omega cluster. But there's a bunch of these things, and what's really interesting is how they form, and as you said earlier, they might tell us something about the age of the Milky Way, because we think that they formed very very early on as the galaxy was forming. You know, the way these things happen is that you get, you know, a big clump of gas and dust, and it may have been that you just got sort of like an over dense pocket of gas and dust something which was like, you know, got more of a serving of globs than the rest of the stuff around it, and it collapsed all at once and made a big bunch of stars. And so these globular clusters, when we look at them, we see a bunch of stars and no gas and dust in between, which means like they're not forming any new stars. So they're sort of like a little time capsule from the very very early formation of the galaxy.

So when you say it happens at the same time, what are we talking about, Like it all happens within sort of one of our human years or is it literally like within a few moments?

Oh wow, No, we're talking like in within millions of years.

Right, Okay, so star times the star time. Yeah, we humans are sort of like dogs. We live in dog years and they live in star years.

Yeah, they live in star years. We think that these globular clusters are about eleven to thirteen billion years old.

Wow.

Now, remember the whole universe is only just under fourteen billion years old, which makes these things some of the oldest things in the galaxy, which is how we can sort of use them to help understand the age of the galaxy, and also when we see them in other galaxies like Andromeda, we can use them to help understand the age of Andromeda. And one way we can do that is because we think that all the stars in there were formed at the same same time, which means they all sort of like start their own clock at the same time. And you remember that the life cycle of a star is that it burns for a while and then one's just done with all of its fuel. It either goes nova or collapses or something. But the life span there depends on the original size of the star. The more mass it has, the faster it burns. The smaller it is, the longer it burns. So we can tell something about the age of these things just by looking at like the distribution of stars, which ones have burned out already, which ones have not. But the fact that they've all formed at the same time makes it very easy to sort of like reverse that back and understand how this thing started.

It's nice from a scientific perspective because you control for the factor of age. You've got like these little test tubes out there that you can look at as physicists.

Yeah, exactly. And they're also an interesting collection of stars because they're not stars like our sun. Our universe has gone through a few cycles of making stars. You know, in the very early universe, you had hydrogen helium that fell together to make the original first generation of stars, which weirdly astronomers called population three stars, and those were really big and didn't burn for very long, but they made some like helium and some heavier stuff, some things that astronomers called metals. And then when they blew up and they spread their stuff through the galaxy, there was a second generation of stars which formed, and those are called population two stars. Some of those burned up and collapsed then spread their stuff through the galaxy to make population three stars, which is like our sun is a population three stars, I see, But these stars in the globular clusters are only population two stars. There weren't any of the population one stars, the ones like our sun when these things formed.

So you may have explained this, So it counts down, it goes pop three, pop two, pop one is the newest.

Or yeah, exactly, which I guess makes the next generation of stars are gonna be what pop zero and then pop negative one, Like nobody really thought this.

Through pop zoomers.

And the other fun thing about these is that that very low metallicity, Like there's basically just helium and hydrogen, because that's what was around after the first generation of stars, the population three stars. You know, astronomers have this weird naming system for basically everything. Well, one thing that's especially weird is what they call a metal, Like everything that's not hydrogen or helium is a metal to them because it's like a big heavy element.

I see. I mean, like, you know, there's a lot of controversy in the metal community of what can be considered metal. There's prog metal, and some people say, no, it's too much of a ballad to be metal, but you know, I think it's nice to be inclusive.

And so these globular clusters that have basically only very low metal stars, and these stars are also not that big, which is why they've been burning for so long, and they might continue to burn for billions and billions of years. More. The smaller kinds of stars, like red dwarfs, they might even last for trillions of years.

So these are very I guess gasy stars would be fair to say.

These are gas these stars. But the interesting thing is that they've sort of cleared out all the gas and the dust inside of them. They're not making any new stars. Other parts of our galaxy still have these big blobs of gas and dusts, so there's still new stars being made all the time, like our Sun was made, you know, fairly recently on these timescales, only five billion years ago. But the globular clusters, they're sort of like you know old boys clubs. They made all their stars, they used up all their gas and dust, and then they're done. They're just like, we're just gonna hang out. We're happy with a number of stars. We have no new members.

Typical. Typical.

There are some places in the universe where globular clusters are still forming, like in the large magallinin cloud there's a big post of gas and people think that it's now forming into a new globular cluster. And by now we mean, you know, within the last twenty million years on.

Star time, star Time, not little human dog Time.

But there's still a lot of really interesting mysteries about these things. Most of them have sort of like a single population of stars that we think all formed at the same time, and you can tell based on like the star ages and sort of how they're like popping off and dying. But some of them have like two or three different populations. It looks like there was a clump all made at once, and then another clump all made at the same time that was different from the first clump. So there's a lot of interesting mysteries there.

So is it more rare for globular clusters to form in our current universe than you think that it was like near the beginning of the universe.

Yeah, absolutely, because a lot of the gas has already turned into stars or into globular clusters, and so it's very rare for globular clusters to still be made. Most of them were made in the early universe, and they're just sort of like hanging around. They're like, you know, the old folks still smoking in the back of a bar, you know, and they're just not really making them like they used to do anymore.

There's just not enough gas to go around, which I can't believe I'm saying.

And so we don't really understand like how these globular clusters have multiple different populations. Like people think maybe different globular clusters might have merged, like had two of them formed at different times and they sort of came together to make one that had two different populations in it. But it's, you know, it's an area of active research. It's not something we really understand.

So could I live in a globular clusters? What's going on in there? Is it? Is there anywhere for me to be?

Are you looking to move, Katie? You're happy with your current apartment.

I've got my cool shades that I currently can't say anything through, So I've gotta gotta find a place as bright as I am.

It's a really fun question because it's fun to imagine what it would be like to be on a planet inside a globular cluster, And so people are wondering, like, are there planets around these stars? Do these stars also have like planetary disks which collapse and give you rocky stuff that you could live on? Could there be alien life that evolved inside a globular cluster. We think, actually it's pretty unlikely for these things to have planets around them, which is a bit disappointing when it comes to like writing science fiction novel about it. But this really two reasons. One is that most of the material just sort of went to making stars, Like there's mostly gas there, so it's hard to form planets. Planets you tend to want to have like a rocky core with something heavy in it, But these things formed in the early universe when there was basically just hydrogen and helium and very small amounts of heavier stuff, so you didn't have sort of the raw ingredients to make planets. And the second is that it's pretty hard for a planet to stay orbiting a star if there are so many other stars nearby constantly tugging on it.

Right, it seems like even if you could have like a gas planet, it would just get ripped apart by these quarreling stars.

Yeah, exactly, and it would just get tugged out of orbit. You know, we think of our planet as mostly just orbiting the Sun, but there are gravitational forces from other nearby stars or things that pass nearby, and when the Sun comes nearby other stars, those things get stronger. So in a glibular cluster, remember it's much much denser. There are many more stars nearby, so these tugs are a lot stronger. So even if you did form a planet and it did survive being pulled apart as you said, it would probably just get like passed around from star to star, wouldn't have like a stable orbit like a volleyball exactly like a hot potato planet.

Well that doesn't sound ideal for me as a little person living on this volleyball planet, So I'm gonna have to rethink my travel plans. So we'll take a break while I look into real estate in a different part of the universe.

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All right, so we are back. I am looking at man Zillow just does not really go into like Beetlejuice area.

There aren't very many sales to track there, so who knows how much those houses cost.

So we're talking about globular clusters. We have found out that I cannot live there inside a globular cluster. Dream shattered. But maybe there's something else we can get out of these globular clusters.

Yeah, we think that there aren't planets around these things. And people actually went and looked and they studied a cluster and one of them had exactly zero planets in them. And then they looked at another cluster and they actually did find one planet. It's this huge Jupiter sized planet, but it's orbiting a pulsar in a binary star system. It's like a really rare and unusual kind of situation, and a pulsar is not the way you want for like your home sun.

Well, so what is a pulsar.

A pulsar is a star that's already collapsed, so it's burned it through its life and it doesn't have the energy to prevent gravitational collapse, and so it falls down into a neutron star and then it starts spinning crazily and emitting crazy radiation into the universe, which then sweeps across the sky and pulses, which is why we call it a pulsar. We have a whole fun podcast episode about pulsars people can dig into. But pulsars don't emit light the same way like our sun does because there's no fusion going on inside. So it would be a pretty chilly place to live.

Well, I'll pack a sweater, pack.

All the sweaters. But there are some really interesting things you can do with globular clusters, like experiments, you can do, questions, you can ask things, you can learn about the universe. To me, what's really interesting is that you get all these stars together, like really tightly packed, and so you get to see like what happens when stars get really dense, when they're like all tugging on each other gravitationally, because you know, normally stars are pretty far separated, they don't really pull on each other that much. So it's like getting to study what happens when they get all crammed together.

It's a star mosh pit.

Exactly, and you get really interesting dynamics. Like some of these things have had what they call core collapse, where the center of the globular cluster has a bunch of really really big stars and all the smaller stars are on the outside, and so they're trying to understand, like, are these because of gravitational interactions where like two stars come near each other and then sort of like throw each other in different directions, and the bigger star always gets sort of thrown a little bit more towards the center, so that after billions of years, you end up with the smaller ones like in the little halo around the bigger ones at the center.

It's like you have a bunch of dance partners and you've got a bunch of little guys and some big guys, and they're doing the dance from you know, the Titanic where you hold hands and you spin around in a circle and then you let the other person go and they go flying. But it's a bunch of stars, and so maybe the little ones, like when they go flying, they fly out out further, keep getting slingshotted out to the outside, whereas the bigger ones don't get tossed or yatd as the kids say as.

Far, Yeah, that's exactly what happens. That makes the core of these things even crazier because not only is it a place where there are a lot of stars, but now you have even bigger stars all clustered towards the center. So the heart of these globular clusters must be a really crazy place to live or even to visit.

It seems slightly deadly.

Potentially, you can also see really interesting new kinds of stars. There's a kind of star that seems to only exist inside a globular cluster. Oh really, Yeah, And these actually I got to give astronomers kudos because they have a cool name. These stars are called blue Stragglers.

Oh man, this sounds like I can just hear sort of like a guitar twying going on and a country song starting about the blue stragglers.

Yeah, they lost their dog and their truck. But the interesting thing about these stars is that usually what happens to a star is one hundred percent determined by how much gas it started with and then how old it is. So you start with a bunch of gas and it burns for a long time, and you know, it's color depends on its temperature, which depends on the gravitational pressure, which depends again on just how much stuff it is. So you get enough stuff, you're gonna have a red giant. You get a little more, you can have a blue giant, for example. And so it's a very like well known, well understood sequence, and stars should only appear like somewhere on this curve that tells you the mass and the age of the star. But inside these globular clusters is a weird kind of star called a blue straggler, and they're much bluer than you expect for a star of that size and that age.

Poor things.

They got the blues, yes, that country music at all.

It's the blues really all right, So why are they so down or are you talking about the color?

Yeah, well, we don't exactly know. It's a fascinating area of study, something people are trying to understand. And that's what's really interesting about these globular clusters. It's like a new experiment. You know. Astrophysicists they don't get to do experiments like particle physicists, where we like smash stuff together to see what happens. They don't just say I'm going to smash two stars together and see what happens.

We don't have a star cannon yet, we can't do it, yeah, exactly.

We asked for funding for the star cannon seventy two trillion dollars, but we haven't heard back yet. But what they can do is just sort of look out into the universe and see if these experiments are already happening, because the universe is chalk filled with weird stuff, and if you look long enough, you'll see something that might answer your science question. And so we think that might be what's happening inside globular clusters, that essentially star collisions happened. That the reason these stars are like two or three times bigger than you expect for a blue star is that they sort of like got captured and fell together and formed an extra big star.

So they just kind of like it's a collision and instead of all spreading out, it all kind of just starts to I hate to say it, but congealed.

Together, coagulated exactly. And you know, that tells us something about star formation, because most stars we see formed outside globular clusters, and that tells us about the distribution. You know, you get a certain amount of helium and hydrogen, you get this kind of star of that kind of star. This tells us that under special circumstances, if you make a bunch of big stars near each other, they can combine together to make a super kind of star, a blue straggler that doesn't appear anywhere else in the galaxy or the universe. It's like a special star laboratory.

And what's the straggler part of the name referring to.

If you look at the curve for where stars are, it's like color versus mass. Then there's this population of blue stragglers that are sort of off the curve. They're like to the left ic and so they're sort of like not hanging out with the rest of them that are like falling behind. You know, you don't want to judge these stars and make them feel bad. They're just sort of different. They're differently starred.

Yeah, they're differently starred exactly.

Globular clusters also give us a laboratory for trying to understand another mystery of the universe, and that has to do with black holes. Black holes form in our universe, but sort of only in two different groups. Like we either get black holes that form when stars collapse, and then they're about the mass of a star. And so we see black holes from stellar collapse and they're out there and they have masses of like ten to one hundred times the mass of our Sun, about what you would expect from the collapse of massive stars. Then there's another whole group of black holes that are like millions of solar masses, and these are the ones at the centers of galaxies. So you got like stellar black holes hanging out in the neighborhood, and then like the really big Papa black holes in the centers of galaxies. And one question in astrophysics for a long time is like where are the intermediate ones? Like why are there no black holes that are sort of like between one hundred and ten thousand solar.

Masses right the Goldilocks black holes?

Yeah, you know, why don't black holes emerge to form the bigger ones? Interesting question about like where they're made and how often it happens, and so this is something people have been trying to understand. And one possibility is that you might be able to make intermediate mass black holes in globular clusters because here you have like an unusual density of stars and if a bunch of them go black hole and then form together, you might be able to make one of these things.

So how are we going to do this? What do we need to make a black hole out of one of these globular clusters?

Well, we don't have to do much. We just sort of sit back like astronomers and look out in the universe that's putting on a show for us. And the idea is sort of wait for one of these things to turn into a black hole, and then if there are a bunch of other black holes nearby, they could sort of swirl into each other. And remember what happens when you toss a black hole into a black hole is you just get a bigger black hole. See, black holes don't like tear each other apart. Anything you tossed into a black hole just makes a black hole bigger. This is one of the favorite things people write in about, like what if I threw in you know, anti mat into a black hole? Or what if I shot a laser into a black hole? Right, you can't destroy a black hole by adding more energy to it. A black hole is just a big blob of dense energy. So the more you add to it, the more black hole it gets.

This is called the Kirby principle.

Is that a cartooning joke.

It's a Nintendo character Kirby. He just sucks stuff up and he gets bigger and bigger.

Awesome. Well, that's exactly what happens, and so black holes can eat other black holes and then become super black holes. Or if you start out with a bunch of smaller ones, you might get an intermediate mass black hole. And that'd be really interesting because maybe intermediate mass black holes do something different from the really big ones or the really little ones. You know, the really big ones are, for example, sometimes they're quasars. They make crazy radiation because of all the gas and dust swirling around them. So this would be like a cool opportunity to just see something new we'd never seen before. And so people are looking inside these globular clusters trying to see if there are these intermediate mass black holes inside of them.

So when you're looking in a globular cluster, is there a trick to being able to find a black hole inside one of these?

Yeah? Great question, because you can't obviously see them directly. The way you can see a black hole is either gravitational lensing of the stuff behind it. So for example, if a star passes behind the black hole, then most of the star would disappear or some of the light from the star would bend around the black hole, and you could see that sort of distortion and actually a globular cluster is a great place to do that because you have a lot of stars moving all around, so it's easier to see this gravitational lensing effect I see.

So the more activity you have, like, the easier it is to see the disruption of that activity as done by the black hole.

Yeah, because you can't see the black hole directly, you can only see its influence on stuff around it, So you can either see it bending the light that comes from behind it, or you can just see its gravitational effects on the nearby stars. Black hole that's at the center of our galaxy. We know it's there because we've seen its pull on the stars that are around it. We see those stars orbiting something that isn't there but obviously has a very strong gravitational pull. And so globular clusters are a great way to see black holes because there are so many of these gravitational probes. If there's a black hole somewhere, you should be able to see its effect on the nearby stars. You can calculate, like, how should these stars be moving if there wasn't a black hole, And then you can see if there's a deviation from what you expect and if that could be explained by putting an invisible heavy mass in one spot, and if so, then you think you've seen one.

So have we found any inside a globular cluster.

So no confirmed sightings of intermedia mass black holes and globular clusters. I know, stay tuned. There was one where people thought maybe they saw one with four thousand solar masses, but then follow up analysis didn't see the same results. And actually you could explain all the star paths without the black hole. And so it's a hard thing to do because these things are not that close by and looking at individual stars in a cluster, you know, thousands of light years away. But it's an exciting thing. It's a it's a cool new object for us to look into and to ask questions about the way stars form and new weird kinds of stars and strange conditions for black holes.

I mean, it seems like a real, just fun happening spot in the universe to really put your papers on. As an astronomer.

Yeah, I think it's really interesting and I love these bits of the universe that are sort of left over from an earlier time. Now, these things formed more than ten billion years ago and they're still around, which gives us an opportunity to learn, like what was going on back then, because what happened back then is what determined the shape and the nature and the content of these things. So they really are like a little time capsule of the early universe. And everything we're doing in physics about trying to understand the universe is about trying to rewind it and trying to understand how did everything happen. So to do that we have to find clues. We have to look for places in the universe where stuff is left over. You know, this is like the astrophysics analogy of a fossil. Yeah, you know, a little piece of evidence left over from an earlier time.

Or like a living fossil, like a sela.

Camp Yeah, exactly, like a living fossil. Unfortunately, there probably aren't any aliens living on planets swinging arounds from star to star inside a globular cluster, but maybe there are, and if so, maybe they could tell us something fascinating about what it's like to live inside such a bright environment.

I'm hoping to find a blobfish inside a globular cluster.

I think that's why globular cluster sounds gross to me because it resonates with the word blob. You know, every time on this podcast I wanted to say globular cluster. I've almost said blobular cluster.

Well, you know, it's interesting because globular clusters do not deserve that kind of nasty name. Likewise, the blobfish actually gets a bad reputation. It does not look like that. Have you ever seen the blobfish. It looks sort of like a sad exploded blob with a frown.

Yes, it's not very appetizing.

No, No, it looks like a slimy blobble. That's because it exploded when you brought it up from the deep sea. Oh, and it's natural environment. I wouldn't say it's a looker. It's not beautiful, but it looks a lot more solid. It just kind of looks like this gray, sort of solid, bony fish. But when you bring it to the surface, it looks like a blob. And so you know you can't trust a glob or a blob by the name.

Well, it must be very disappointed. You know. It looks at itself in the mirror before it leads the house, and it's like I'm looking good, and then it ends up looking like a big blob when it's brought.

Up to the surface, and they truly do look quite pathetic because it looks like they're frowning. But maybe the globular clusters and the blobfish can come together and get some better pr for themselves.

Maybe the aliens that live in globular clusters look like blobfish and they'll come here and they'll recognize the blobfish as you know, really the the people they want.

To talk to. It seems like you'd have to be sort of blobular to live in a globular cluster because of all those stars tugging on you all the time.

Like Taffy, your planet would be a bit of a blob as well. All right, well, thanks everyone for sharing your curiosity with us and taking this tour of a fascinating structure inside our galaxy, something that can tell us all about the universe and how stars formed and the age of our galaxy and maybe about the future of black holes.

Yep. So when someone says, hey, would you like a globular cluster, don't turn your nose up at it. You could teach you about the deepest secrets of.

The universe, but please don't use that for your next breakfast cereal. All right, everyone, thanks for tuning in, See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple podcast Us, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.

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Daniel and Jorge Explain the Universe

A fun-filled discussion of the big, mind-blowing, unanswered questions about the Universe. In each e 
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