Daniel and Kelly’s Extraordinary Universe - Could our galaxy have a dark matter center?

Episode Date: January 25, 2022

Daniel and Jorge explore the idea that the center of the galaxy might hold a huge blob of dark matter rather than a black hole. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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No such thing. Hey, Jorge, do you like a surprise candy center? Hmm, it depends. Does it depend on what the surprise is? Absolutely. You know, if it's duce de leche, yes, sign me up. If it's like marshmallow, I know thanks. Well, I guess that makes sense.

Yeah, also it depends on what is it surrounded by? Like, what is it the center of? Like, I don't want to surprise candy center in my taco or pizza. How about a surprise guacamole center in your taco? You mean, like, candy guacamole? Not too sure about that. How about candy, guacamole? in your dessert taco.

Ooh, dessert taco. Now you're talking. Can we put bananas in it? Banana and avocado-flavored ice cream. I'm not so sure this was a great idea. Yeah, we went too far. Hi, I'm Horhammy cartoonist and the creator of PhD comments. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine and I will always try a weird flavor of ice cream.

Really? Have you tried a garlic ice cream? I have. I've tried garlic ice cream. I even tried pasta fajoli flavored ice cream. I've tried licorice ice cream. I've tried all the ice cream. Man, there's a lot happening in your laboratory there. I'm married to a biochemist, you know. She can really cook up some crazy stuff. As long as she doesn't put a gut bacteria in your ice cream. That's what she researches, right? That's true. Well, there's that famous Nathan for you episode about poop-flavored ice cream. What? Somebody made that? Or somebody made that accidentally? No, there's a company apparently which will create any flavor for you. So they created artificial poo-flavored ice cream and just to see if people would try it. Oh, boy. Have you tried a durian flavored ice cream?

No, I haven't been able to find that yet. Well, there you go. That's not too far from some of these extreme flavors. But welcome to our podcast, Daniel and Jorge, explain the you. a production of iHeard radio in which we take a deep bite of the universe hoping to enjoy its flavor whether it tastes like black holes or neutron stars or swirling masses or tiny little particles we are here to savor it with you because we want to know what the truth is out there in the universe regardless of how it tastes and so we don't shy away from taking a bite of any of the biggest questions in the universe where does the universe come from what does it all mean what's really

going on on a tiny quantum scale. What's swirling around in the center of our galaxy? How does it all fit together? We talk about any end, all of those questions, and explain them to you. Yeah, because it is a wonderful and tasty universe. Now, Daniel, do you think we were taking bites out of the universe, or are we just licking it before it melt? What is the universe going to drip onto in this analogy?

That's my question. You know, a universe cone, obviously, hopefully a waffle cone. Maybe physics is like the napkin because we're trying to wipe up. up the messes. I see. You're not trying to create the messes. I thought physics was like the tongue doing the licking. I don't know.

This is getting very strange. We are definitely mixing our metaphors here. But, you know, the universe is delicious. The thing that I love about physics is that every time we do take a bite out of the universe, we find something amazing. It's pretty rare that you uncover some mystery and then go yawn. That was boring. The universe has lots of impressive surprises for us. Yeah, even I hear it has Higgs boson flavored ice cream.

And also some cork ice cream as well? Or is all ice cream, quark ice cream? Everything is cork flavor. That's right. In the end, the corks are the fundamental basis of flavor. And of course, we do have flavor physics, which talks about different kinds of corks, but totally ignores the question of what they taste like. Oh, boy.

We're getting inception here. We're like going down a few levels. It's like exploring the flavor of the particles, the makeup flavor? That's right. And, you know, it's not just stuff here on earth that you can taste. The astronauts report that space itself has a flavor. What? What do you mean?

It tastes like a vacuum? We talked about one time on the podcast here. When you come back in from a spacewalk, there are little volatile molecules from space that have stuck to your spacesuit. And when you enter the atmosphere, they boil off and smell like barbecue. And sometimes people say like a raspberry. Whoa, really? Like, I guess there's like little tiny particles floating in space of raspberry and possibly barbecue.

Yeah. And some of the gas clouds near the center of our galaxy are supposed to smell a little bit like cranberry, though nobody's ever been there. As long as it's not raisins. Now, are you sure when they came in from the spacewalk, the barbecue they're smelling is not themselves from being out in the sun too long? Gee, it smells like my hair is on fire. What's going on? It smells like cosmic ray fire. But anyway, it is a pretty interesting and amazing universe, and there's still a lot we don't know about it, even in our own neighborhood. There are big mysteries in our solar system and especially in our galaxy.

Our galaxy is called the Milky Way and it's big and it's amazing. It has millions of stars. But there is a big mystery at the center of it. Because remember that everything we know about the universe and our galaxy comes from observations we have just made from here on Earth. Yeah, we've sent a few probes maybe to the edge of our solar system. But mostly we have one eyeball trapped here in one spot in the galaxy. And we're trying to do something very difficult, which is make a map of the solar system. the whole galaxy, of the whole universe, having seen it from just one spot. Imagine standing on the

top of a mountain and then trying to make a map of the earth. Some things are obscured from your view. Other things you have to just sort of sketch because you can't quite make them out. That's the challenge we face in trying to map out the cosmos around us. Yeah, and it's pretty amazing how well we've done. You know, just from standing it in that mountain with a telescope, we've been able to basically figure out most of what the universe looks like and how it's structured together and how many stars there are out there, how many galaxies, but there are things that we can quite see from our point of view. Yes, sometimes we can be very direct and say, look, we see that thing, we know exactly what it is and where it is. Other times, we have to sort of infer what we think is going

on based on more indirect evidence. And that's how we've leveraged our powers of observation to tell us about how things look in places that we can't see. We have to make these indirect conclusions. But sometimes we might make mistakes because we might be folding in incorrect assumptions or guesses about what might be there. And people can come along with new ideas that give us new perspectives on what's going on. Yeah, you could be licking the wrong ice cream for all we know, right? There is no wrong ice cream, man. Well, wait till you taste during ice cream or that poop ice cream. That sounds like the wrong kind of ice cream. But yeah, it is a pretty mysterious galaxy that we live in. And so today we'll be tackling a question.

related to what's at the core of it. So on the podcast today, we'll be asking the question. Could our galaxy have a dark matter center? Hmm. Could our galaxy have a dark matter center? Now, isn't dark matter all over the galaxy? Like, isn't most of our galaxy made of dark matter? Yes, most of the mass in the galaxy is dark matter.

And there is definitely dark matter hanging out at the center of the galaxy. But conventional wisdom is that the center of the galaxy also has a super massive black hole as a like gravitational anchor, something that's really holding the whole galaxy together. This incredibly massive object four million times the mass of the sun. But we've never seen that black hole directly. And so some people wonder if it's really there or if instead it's dark matter doing the work. Interesting. Yeah, because I guess we can't sort of look directly into the center of our galaxy.

I mean, we can sort of look in the direction of the center of the galaxy, but it's so far away, maybe, and there are so many things in between that it's hard to kind of see in there. It is in fact completely obscured because the center of the galaxy is a busy place. There are a lot of stars between us and it, and there's also a lot of gas and dust. So it's not something that's very easy to look at directly in the visible light. And so we'll get into the details of what we know about what's going on in the center of the galaxy, why most astronomers think that there is a black hole there and some new evidence that's casting doubt. on that assumption. I see. So the prevailing thought is that there is a super massive black hole in the middle of our galaxy.

But now the question is maybe there's not. Maybe it's just a whole bunch of super compact dark matter maybe? Yeah, in line with our podcast about dark stars, we are casting doubt on the existence of black holes everywhere. We are throwing shade on black holes because in the end, they are very difficult to see directly. It's always an inference. You're always jumping to a conclusion saying there's a certain amount of mass and a certain amount of area. Therefore, it must be a black hole. But, you know, that's not like finding the body in a murder.

It's all circumstantial evidence. Yeah. And the problem with throwing shade at a black hole is that it never comes out. It just eats your shade and says, thank you. Can I have another? It's a pretty interesting question. What is at the center of our galaxy? Is it a supermassive black hole or is it dark matter?

And so as usual, we were wondering how many people out there had thought about this question and think that maybe it could be dark matter. So Daniel went out there into the internet to ask people, Could our galaxy have a dark matter center instead of a black hole? So thank you very much to our cadre of volunteers. If you'd like to join them, please don't be shy. Just email me to questions at danielanhorpe.com. You know you want to.

So think about it for a second. Do you think our galaxy has a dark matter center? Here's what people had to say. There is lots of evidence for a black hole from a high concentration of mass at the center of our galaxy because of the orbit of several stars. that have been whipping around something very, very small, very, very fast. So that implies a density of matter far in excess what we normally would predict for dark matter,

and if the dark matter were to concentrate to that extent, it would then just become a black hole, since it is only gravity that matters anyway. I don't know why our galaxy would have a dark matter center instead of a black hole? I know that most galaxies do have a black hole at their center. As do most spots where enough mass has just gotten together and hung out for long enough, maybe it could be both?

Could our galaxy have dark matter center instead of black hole? I know I think we have a supermassive black hole in the center of our galaxy, not dark matter. I don't really see how we could have a dark matter only center of our galaxy. our galaxy because that would mean that all the regular matter is being pulled into it which in my head would make it a black hole whether or not the dark matter falls into the black hole it's kind of irrelevant because you've got a black hole there anyway pulling in any barionic matter i do think that the galaxy can have the dark matter center because

dark matter experiences gravity it has it has mass and it definitely experiences gravity It accounts for, like, a very large amount of matter that we know of. So we only know that normal matter is very less. And, yeah, there is a possibility that there is a huge quantity of dark matter at the center of a galaxy instead of having a black hole. Ooh, tricky, tricky, tricky, tricky. I have no idea, but it reminds me of something in a video game I used to play. I'm just going to leave this one as a shrug.

All right. It seems that people are skeptical. Yeah, there's some great answers here. People thinking about what would happen to the dark matter, if it got concentrated at the center of the galaxy, really some great stuff. Yeah, I like the people who say it could be both. Like, yeah, why can it have both? Both a super massive black hole and dark matter in it.

Or how about a dark matter black hole? A dark matter black hole would be super awesome. Although, you know, once material falls into the black hole, it's not really clear what its nature is anymore. Or is it still dark matter? Has it gotten converted into energy? It's gotten turned into something else. So once you're inside the black hole, it's just stuff, man.

Whoa, yeah, because I guess dark matter could technically turn into regular stuff. Do you think it's made out of the same kind of like energy? We don't know, right? There might be some way for dark matter to turn into normal matter. We do know that there was a lot more dark matter in the early universe than there is today. And so we hypothesize that there's some mechanism by which dark matter can very slowly turn into normal matter. but it needs a lot of energy density for that to happen. So we think it might have happened in the early universe and then frozen out

and it might then again happen inside black holes, who knows? Maybe throw a lot of shade to the black holes and lost some of its energy. All right, well, let's tackle this question. Could it be dark matter at the center of our galaxy and not a super massive black hole? Now, first of all, I guess, why did we think or do we think that the center of our galaxy has a supermassive black hole? Well, let's not be too clickbaity. Definitely the mainstream astronomy community is convinced that there's a super massive black hole at the heart of our galaxy.

I mean, they gave the 2020 Nobel Prize to two folks, Reinhardt Gensel and Andrea Gess from UCLA, who've been observing the center of the galaxy for decades and trying to figure out what's going on there. But we've had a hint that there's something going on at the center of the galaxy for decades, since people sent up rockets into the upper atmosphere and heard this radio signal from the center of the galaxy. And then it was in the 60s and 70s that people figured out, oh, wow, maybe this could be a black hole. And it was one of the first things identified as a black hole at the center of our galaxy. That's interesting because I think we talked about this in another

episode where, you know, we talked about how do we know there's maybe a black hole at the center of our galaxy. And I remember one of the ways is that you can tell from like how the stars around the center of the galaxy are moving, like they're moving faster or they're in tighter orbits than you wouldn't have if you didn't have a black hole yeah you can never see a black hole directly right it's just black it's essentially invisible so what you need to do to identify a black hole is to see its gravitational effect on stuff around it and so the argument that something is a black hole is that you measure its mass by looking at how hard it pulls on things gravitationally nearby but then the second crucial element is that you need to measure its radius because not everything

with gravity has a black hole right the earth has gravity you can measure its pull on the moon, doesn't make the earth a black hole. But if you can measure something's mass and its radius and the radius is really, really small, that means that the object is really dense. It's very compact. And below a certain radius, an object of that mass has to be a black hole as far as we know. Oh, I see. You're saying that we know that there is something really heavy at the center of our galaxy, super duper heavy, but we don't know if it's actually a black hole. Like, it could just be a giant ball of ice cream, right? It could be all that during an ice cream that people have been rejecting for all of those years.

Yeah, nobody wants to lick, yeah. And so the tricky thing is the radius. And as you say, a great way to study this is to look at the effect on very close by stars because they're mostly affected by the gravitational pull of this thing. And also, as they pass close by, you can get a sense for how big the black hole is. Because if something passes within one AU, for example, and survives, then you know that whatever's there has to have a radius of less than one AU. where AU is an astronomical unit

the distance from the earth to the sun. And that's exactly what they do is they look at all the nearby stars. This is like a few stars that hang out really close to whatever this is at the center of the galaxy and they zip around it. So people look at the motion of those stars to try to measure the mass of this object.

And they also look at the distance of closest approach to try to get a sense for what the radius of this thing might be. So wait, you were saying that we can sort of look at the center of the galaxy. We can see these stars. orbiting around the very center of the Milky Way? Well, it's not easy, and you can't see them in visible light, but infrared light can pass through a lot of the gas and the dust. So if you use filters on your telescope to only look through the infrared, you can see

these stars, and in that way, you can see what's going on in the center of the galaxy. And if you Google, you can watch these cool movies of these stars, and the movies take like more than a decade to make because these stars have like an orbital period of like 16 years. but you can see them whooshing around this blank spot at the center of the galaxy. Oh, wow. So it's really obvious that there's something very massive there. Interesting. So we do have sort of pictures of the center of the galaxy.

You can sort of see through that gas and dust, and it does show something pretty dense in the middle of it. That's right. So we can measure the mass pretty accurately to be about 4 million times the mass of our sun. It's very, very heavy. It's an incredible gravitational source. But the tricky thing is that we don't have a great measurement for the radius. of this thing, because in order to measure the radius, something has to pass really, really close

and then survive, right? It has to, like, not fall into the black hole. There's a start that's called S2 that goes really close to it, but the closest approach we've ever seen to this object is about 12 a.U, 12 times the distance between the Earth and the sun. Wow, that seems really small to me, right? Kind of, right? Like, it's smaller than our solar system. Like, this thing, whatever it is, the super dense thing at the center of the galaxy is smaller than our solar system. It is smaller than our solar system, but... But it's four million times of the mass of our sun. Four million times the mass of the sun.

But if you calculate how big should a black hole be, if it's four million times the mass of the sun, then you can an answer of like 0.1A.U, like a tenth of an AU. So whatever this thing is, it's much smaller than sort of the radius we've been able to probe. Right. It might be a black hole that's really dense and at the heart of this. sphere we haven't been able to see inside of yet. But that's the uncertainty. We don't really know if whatever this stuff is that has mass of four million times the sun is actually compactified enough to make a black hole or if it's something else, something sort of larger and fluffier.

Right. Like you could take four million times the mass of our sun in ice cream and put it in a giant ball and probably would it be about that, you know, smaller than the size that we're observing? Like could it be like, you know, four AU? Yeah, 12 AU is a real. really large radius. And so it makes a huge volume. And so even though four million times the mass of the sun is a lot of mass, if you spread it out through a sphere that's like 12 AU and radius, it's not actually that dense. So yeah, you don't have to be nearly as dense as a black hole. It's still a little bit denser than durian ice cream. But, you know, it's pretty close. Dense in flavor, at least. All right. So that's kind of the mystery. We know there's something

super heavy, four million times the mass of the sun in the center of our galaxy. But we don't know how dense it is, whether it's dense enough to be a black hole, or maybe it's just dense enough to be a big ball of ice cream or dust or cloud, or who knows. So let's get into why would not be a black hole and what evidence we have for either answer. But first, let's take a quick break. kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass.

The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy?

That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers, the pilot is having an emergency and we need someone, anyone, to land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, until this. It's just, pull that, turn this. I'm Manny. I'm Noah. This is Devin. And on our new show, no such thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence.

Those who lack expertise lack the expertise they need to recognize that they lack expertise. and then as we try the whole thing out for real wait what oh that's the run right i'm looking at this thing listen to no such thing on the i heart radio app apple podcasts or wherever you get your podcasts your entire identity has been fabricated your beloved brother goes missing without a trace you discover the depths of your mother's illness the way it has echoed and reverberated throughout your life impacting your very legacy Hi, I'm Danny Shapiro, and these are just a few of the profound and powerful stories I'll be mining on our 12th season of Family Secrets. With over 37 million downloads, we continue to be moved and inspired by our guests and their courageously told stories.

I can't wait to share 10 powerful new episodes with you, stories of tangled up identities, concealed truths, and the way in which family secrets almost. always need to be told. I hope you'll join me and my extraordinary guests for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Right, Daniel, we're asking the question, what is at the center of our galaxy, and it could be a supermassive black hole, or it could be something else. All we know is that it's super heavy. It's four million times the mass of our sun.

And it's pretty small. It's smaller than our solar system, but maybe not small enough to be a black hole. So how could it not be a black hole? Like if you have that much mass, four million times the mass of our sun in that space, wouldn't it eventually collapse into a black hole anyways? Well, it depends a little bit on what it is, right? Things don't always collapse into a black hole because they have ways of resisting that collapse. Like, why doesn't this sun collapse into a black hole immediately?

Well, because it has fusion. That energy is pushing. out and keeping the sun fluffy. Why doesn't the earth collapse into a black hole? Because of the strength of the materials, right? They have this actual tensile strength to resist being crushed by gravity. And as things get denser and denser, there are all these thresholds to overcome. Like even neutron stars, which are crazy dense, are resisting collapse into a black hole because of the quantum degeneracy pressure. Like all these corks don't want to be on top of each other. And so in order to become a black hole, you have to have enough mass and already be compact enough.

to collapse, to overcome all of these sort of thresholds. So it's possible to arrange this much mass in that small space that doesn't collapse into a black hole. But I guess, you know, if you had four million times the mass of our sun in it, and if it was just gas or dust, wouldn't, you know, don't we have models that say what would happen to something like that? Like if it had fusion, keeping it from collapsing to a black hole, it would be shining and we would see it, right?

Yeah, so clearly it's not shining. But there's also questions about like velocity. If something is swirling really, really fast, then it's hard for it to collapse. That's why, for example, dark matter doesn't collapse into a black hole because dark matter has a lot of rotational energy. It's swirling around the center of the galaxy. And in order for it to collapse into a tiny point, it needs to lose some of that angular momentum. An angular momentum is conserved in our universe. So the only way to lose angular momentum is to like bump into something else and give your angular momentum away.

And that's really difficult for dark matters to do because, as we talked about before, it's not sticky. So it's possible that whatever's there is just swirling around for a while. But there are also other explanations. And people have a very specific theory for what could be at the center of the galaxy that's resisting this collapse and has the same mass. Well, I guess maybe let's take a step back. You said the prevailing theory is that it is a black hole. So what makes people think that it is a black hole if we don't really have direct evidence of it? I guess it's just the leading candidate, you know, of the things that could have that mass and that radius and not give off any direct light, a black hole is sort of the least exotic.

You can come up with other things, but usually they require inventing new particles, things that we haven't discovered yet. So there's no way to arrange like normal matter as far as we know into a configuration like that that's going to be stable and lasts a long time and not collapse into a black hole. Like even a big swirling cloud of gas that's spinning and resisting falling into a black hole eventually will collapse into a black hole because it'll bump against itself and lose its angular momentum. So you need some sort of like new kind of particle. I see. So as far as we know, if you did have a giant ball of ice cream that big, it would sort of collapse into a black hole eventually. Yes, exactly. It would be a durian flavored black hole.

Yeah. And that one you don't want to lick. I feel like we're going to get so much hate mail from durian lovers out there. Don't write as hate mail until you've actually tasted during an ice cream and can vouch for its deliciousness. All right. So then that's the leading candidate because any other explanation requires a new theory or a new particle or something super exotic. You know, as far as we know, the universe dictates that something that big would fall into a black hole. So that's kind of why we think there is a black hole.

It is. And it was very widely accepted until recently. What happened? Well, there's this really cool astronomical experiment. You know, astronomers don't get to do what particle. physicists do, which is like design collisions. I could like say, I'm going to smash a proton into an electron or let's try shooting muons at this thing and see what happens. Astronomers don't get to do that. They don't get to build colliders and smash two black holes together. They just have to wait for

stuff to happen in the universe in a place that they can observe it. So they have to get lucky. And about 10 years ago, people realized that there was this huge cloud of gas called G2, which was headed for the black hole. It was going to make a really close approach. In our galaxy or in another galaxy? In our galaxy. It was heading right for the center of our galaxy. It was going to make a near miss of the black hole. And they thought this would be really cool

because it allows them to really study the black hole in a new way. Let's throw something at it and see what happens. It let them test the details of this encounter between the gas cloud and the black hole. So you could see this gas cloud. Like you can see it through the cloud of gas in the center of the galaxy. can see it like that there was one nearby? Yeah, you can see x-rays coming out of this thing. And so you can watch this cloud of gas. And everybody got really excited because they were not sure what's going to happen. It sort of reminds me of when everybody saw that comet that was going to smash

into Jupiter. Like we saw a comet coming into the solar system and then people calculate its trajectory and they're like, oh, yay, it's going to hit Jupiter. How exciting. Yeah, it's exciting unless you live in Jupiter. If you just bought real estate in Jupiter, I'm sorry, your investment is a waste. But, you know, but astronomical collisions are a great way to learn about stuff. So people got really excited, and this is like seven years ago or so, and they had all these calculations for what they expected to happen when this gas cloud passed near the black hole. Interesting, like sprinkling dust into a swirling toilet bowl, right?

Kind of, like what's going to happen to it? Is it going to stay together or is it going to get shredded apart? Yeah, and the calculations suggested that this thing should be totally shredded. I mean, a gas cloud is not really held together very. tightly. It's just a big, loose cloud of gas. And what happens when you get near a black hole is that there are huge tidal forces, right? Remember, tidal forces are gravity trying to pull you apart because if part of you is closer to the black hole than another part, then the part that's closer is getting pulled on harder than the rest of you. And so the gravity essentially is trying to pull you apart because it's pulling on bits of you with different forces. So they expected that when this gas cloud came close to the black hole, it would be totally shredded by these tidal forces. But wait, how close did it get? I thought we could only see up to like 12 AU. That's the closest that anything has ever come to the black hole.

This gas cloud wasn't going to get that close. It was going to approach like a couple hundred AU. But close enough that you could get some information about the black hole. You know, you can get some like distant information about the black hole just by measuring the gravitational effect on nearby stuff. You could measure, for example, like the slope of the gravitational field. Right. But that far away, wouldn't a black hole act the same way as a giant ball of ice cream?

Yeah, absolutely. If you stay outside of the heavy object at the center of the galaxy, then you can't tell the difference gravitationally between a black hole or a ball of ice cream or a giant space taco, as long as it has four million solar masses. They would all have the same gravity from the outside. You're absolutely right. So you can't use a gas cloud at like hundreds of AU to help understand what's going on inside the 12 AU radius where we think there's a black hole. But what if it's not actually a black

hole? And what if it's not actually contained within the 12 AU? What if it's something else much larger and fluffier, bigger than the 12AU? If it's a big fluffy mass that's hundreds of AU wide with a very, very dense core, then it could still look like a black hole to the stars orbiting a 12 AU, but it would have a very different effect on the gas cloud. So I talked to Grant Weldon. He's an astrophysics grad student at UCLA who actually works in Professor Gess's group. She's the recent Nobel laureate who studies the center of the galaxy. He said, think of it like a fog that all the objects in the galactic center sit in. The idea is that if it's not a black hole concentrated within that 12AU, but instead some bigger, more extended mass larger than the 12AU,

then it wouldn't have the same tidal force effect on the cloud because the gas cloud G2 would be passing partially inside this new fluffy blob. So the tidal force calculations that assume a big mass within the 12AU would be wrong. But I guess the point is that this gas cloud survived. Like it didn't get shredded as if it would if there was a black hole in the middle of the galaxy. Yeah, everybody was expecting this thing to get totally torn apart by this black hole or whatever is there. But instead, it survived.

It passed right by and it mostly held its shape. You know, it got a little bit twisted up. But it was not totally pulled apart the way that you would expect. for a gas cloud passing by this massive gravitational object. So that was a real mystery. People were like, hold on a second, what's going on. This isn't described at all by our calculations. Wow.

Maybe the gas cloud was made out of Duran, and the black hole was like, I don't want any. I don't want to lick this thing. Totally explains it, right? When you're getting rejected by clouds of gas, wow, you must really be stinky. So then that threw some shade on the theory that maybe there's a black hole, at the center of the galaxy, like maybe it's not a black hole. Exactly.

People started to think maybe we should consider some alternatives. Are there other ways we can explain what happened to this gas cloud other than a black hole because that would be then consistent with all of our observations? And that's when people started drilling into this question of how well do we know the density of this object? Is it possible that there's something actually much larger there, not actually a black hole, but something really much more extended, fluffier and broader and not actually a black hole. Interesting. Right. Yeah. I guess everyone just assumed it was a black hole, but now you have

this evidence that maybe made people go away and how do we actually know that? Yeah. And so people have been creative and there's this really fun theory of a new kind of dark matter. It's called dark inos. So this would be little particles that make up dark matter. They call them darkenos. And these are fermions. And fermions are a kind of fundamental particle. They're sort of like electrons and quarks, they have this really important property that they don't like to be on top of each other. They don't like to share the same state. You know how electrons, for example, if you put one around an atom, it fills up a state and you put another one there, it can't go into the same energy level, has to go into the next one. And it's because they're fermions. They don't like to

ever occupy the same quantum state. So the idea is that these dark matter particles, these dark inos are fermions. So they can coalesce gravitationally, but they resist collapsing into a black hole because of this quantum degeneracy pressure, this poly exclusion principle that keeps them from getting too dense. Whoa, whoa, wait a minute. You're saying maybe it's not a black hole, and so therefore your go-to explanation

is to invent a totally new kind of matter. Another new kind of matter? Like, aren't there other explanations using regular matter that could explain this giant ball of stuff in the middle of our galaxy? Well, we talked about a few minutes ago, any kind of normal matter is going to eventually coalesce into a black hole.

And whatever's there has been there for a long, long time. And so it would have time to collapse into a black hole. So you need something which has a new property of not collapsing into a black hole. So you have to give it this like, you know, quantum degeneracy pressure or something in order for it to survive this crushing gravity. Didn't you mention like a neutron star maybe or some other kind of dense object? Neutron stars can only be up to like two times the mass of the sun.

If it gets any bigger than they collapse gravitationally. So this thing is four million times the mass of the sun. Neutron stars are a really very special case of avoiding a black hole. What if it's 2 million neutron stars kind of orbiting around each other? Like a beehive, you know, like I guess that would also eventually collapse too. It would also eventually collapse. And neutron stars are not black, right? They do emit.

They're super hot and they glow. They emit x-rays. And they spin also. And we can actually see hot spots on the surface of neutron stars because they emit x-rays. because they emit x-rays. There's a telescope on the International Space Station called the nicer telescope, which looks just at those kind of objects.

So in order to explain this, like, maybe new, fuzzy, fluffy stuff at the center of the galaxy, they had to use these new particles with this special property. Okay, so then you're saying this possible explanation for this heavy mass that's maybe not a black hole at the center of the galaxy. So it's dark matter, but now you're sort of positing what dark matter is. You're saying dark matter is maybe made out of,

a certain particle called the dark keynote. Yeah, and this would give dark matter the property that it needs to avoid collapsing into a black hole once it's already gotten into this little area of 12AU and having four million times the mass of the sun. Right, because I think we talked about this in another episode that dark matter can itself turn into a black hole. Like if you get enough dark matter in a small enough space, it will create a dark matter black hole.

Exactly, because anything can create a black hole that has mass. The cool thing about black holes and the cool thing about. about gravity is that they talk to anything that has mass, anything that has energy. So there are a really cool way to probe things in the universe that are otherwise totally invisible to us that we might otherwise have no way to interact with. So if dark matter falls into a black hole,

it just adds to the mass of the black hole. It is challenging, however, to create a dark matter black hole because it's hard to get dark matter that dense. Dark matter tends to be diffuse and it tends to be sort of fluffy. And it's hard to squeeze it down because there are no other interactions. it's not sticky like other kinds of matter. I see. So then you're saying the possible explanation is not really a new kind of matter.

It's just like maybe it's helping us pinpoint a specific property of dark matter that would allow it to become a dense black hole object without turning into a black hole. Sure. Yeah. I think people in the dark matter community would say that this is a new kind of matter. And it's definitely not like the number one candidate for dark matter otherwise. I see. And these particles are not like everybody's favorite dark matter theory.

But they do have the properties you need that if you put them together and create this object of darkenos at the center of the galaxy, it's fluffy enough that it can explain why this gas cloud survived. I see. And it doesn't collapse into a black hole. You're saying because of its quantum properties. Like it has this exclusion principle that lets it not collapse. Yeah, precisely. And you know, it's a little bit cooked up, right? They've created this idea. They've cooked up these darkenos just to solve this problem. So it's not like something we otherwise already thought existed. We have good evidence for, oh, look, it also explains this, right? It's a little bit more descriptive. So you've always got to be a little bit more skeptical when somebody is cooked up a new idea just to explain one particular observation.

Really, you've got to test it in other places. You've got to see like a symphony of results that are all telling you the same story. Yeah, I'm always skeptical when there's a physicist doing the cooking. So that's a possible explanation for what could be inside of the center of our galaxy. and let's get into what the answer is. What does the evidence say? Is there a black hole at the center of our galaxy? Or could it be a big ball of this dark kino dark matter?

But first, let's take another quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious.

Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week. on the OK Story Time podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy?

That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both the meat. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers. The pilot is having an emergency and we need someone, anyone, to land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, until this. Do this, pull that, turn this. It's just, I can do my eyes close. I'm Manny.

I'm Noah. This is Devin. And on our new show, no such thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then, as we try the whole thing out for real. Wait, what? Oh, that's the run right

I'm looking at this thing Listen to no such thing On the I Heart Radio app Apple Podcasts Or wherever you get your podcasts I had this like overwhelming sensation that I had to call it right then And I just hit call

I said you know Hey I'm Jacob Schick I'm the CEO of One Tribe Foundation And I just wanted to call on And let her know There's a lot of people battling some of the very same things You're battling

And there is help out there The Good Stuff Podcasts season two takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community. September is National Suicide Prevention Month, so join host Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. I was married to a combat army veteran,

and he actually took his own mark to suicide. One Tribe saved my life twice. There's a lot of love that flows through this place, and it's sincere. Now it's a personal mission. Don't have to go to any more funerals, you know. I got blown up on a React mission. I ended up having amputation below the knee of,

my right leg and the traumatic brain injury because I landed on my head. Welcome to Season 2 of the Good Stuff. Listen to the Good Stuff podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. All right. What's at the candy center of our galaxy? Is it marshmallows? Is it Dulcea lece? Is it guacamole? Or is it a new kind of dark matter called a dark kino? Which, um, ironically, it tastes kind of like Dulce de leche a year. How do you know what darkiness tastes like? I've been there, you know.

Really? They offer free samples. All right. I'm packing my bags. Let's go. So yeah, we thought for a long time it was a black hole at the center of our galaxy, but maybe it's not. And so the only other thing that could explain it is something called a darkina, which is a kind of dark matter that doesn't collapse when it gets that compacted. So what does the evidence say, Daniel? Where's it thinking in the physics community? I think the physics community reacts to this idea like,

hmm, that's cute, but probably not. It hasn't really persuaded a lot of astronomers. And one reason is that it's not so easy to understand how you would make such a big ball of dark matter. As we've talked about a few times, dark matter is big, it's fluffy, it's diffuse, it's swirling around the center of the galaxy. And so we don't know like how you would get it to collapse.

Like if I gave you a serving of dark matter that had the mass of four million suns, It wouldn't be easy for you to force it into that densen area. So we have no story for how this thing could have formed. Right, because as far as we know, dark matter is not very sticky or not sticky at all, right? Like if you have a bunch of dark matter in space, it's not going to come together and clump naturally. It's going to get attracted to itself, but it's going to keep flying past itself and keep flying past itself to the point where it would just be a fluffy cloud, maybe forever. Yeah, and people have done simulations to test this and say, well, what if,

dark matter are these kind of darkenop fermions and you have a big galaxy size blob of them, what happens? And you just don't get this kind of core. You don't get this like really dense ball in the center that would explain the data. Now, if you happen to have that dense ball in the center of the galaxy, it can't explain what happened to this gas cloud, but nobody understands how you would make such a dense blob of dark matter. It doesn't arise naturally in our simulations. I see. But these simulations are based on what we know about dark matter, but we don't really understand dark matter. So could dark matter have some sort of property we don't know about that would make it clump like that? It would need to have some sort of other self-interaction,

right? Some way to get sticky so that it tends to clump. Someone would to like bump into itself and lose its angular momentum so it doesn't just orbit forever and it falls into itself somehow. But nobody has a theory of dark matter like that that's also consistent with everything else. We're pretty sure that dark matter doesn't have a very strong interaction with itself. We've seen huge clouds of dark matter passed right through each other. Now, the bullet cluster, for example, it was a collision of two huge galaxy clusters, each of which had a lot of dark matter.

But the dark matter just passed right through itself to the other side. Even though there is some gravitational attraction between the two clouds of dark matter, that's really pretty weak. So we're pretty sure that dark matter does not have any very strong interactions with itself. And so it's really hard to explain how you would get a dense clump of dark matter

at the center of the galaxy. There's just like no way to get it there. Right. Even if you give it these interesting quantum properties, it doesn't work out. Like you said, simulate it, it still doesn't clump. But remember that also we have questions about how black holes form, right? We have a pretty good theory for why black holes can form at the center of galaxies, but we don't really understand how they got so big.

So it's sort of a similar question. You know, if you simulate black hole formation in galaxies, they get big, but they don't get as big as the supermassive black holes that we see. So that's also an open question. There's just a lot we don't understand about how the centers of galaxies form. So you can criticize this theory for like, well, yeah, maybe that's what it's there, but how can you explain how it got there? We can't explain how black holes form at the center of these galaxies either. Whoa. I see.

So just because you can't explain how it got there, it doesn't mean it's not there. Yeah. Because we don't know how the black hole, even if it is a black hole, we don't know how the black hole got there. That means it could still be dark matter? It could still be dark matter. I think prevailing wisdom is still that is probably a black hole. And people have been creative in trying to find other ways to explain why the gas cloud wasn't torn up, even if it is a black hole.

Like Andrea Ghez, the UCLA professor who won the Nobel Prize, she suggested that maybe it's not actually just a gas cloud. Maybe inside this gas cloud there's like a string of stars that have the gravitational like strength to hold the gas cloud together. And that's why when it passed near this object, it wasn't actually torn to It has, like, more gravitational self-consistency than people imagined. I see. Maybe that's why it didn't get shredded.

Like, it wasn't just a gas in that cloud. Yeah. And she has a very specific prediction for, like, a binary star system inside this gas cloud that could really hold it together. So when it passes by, like, keeps its consistency. It doesn't get pulled apart by the black hole. I see. Now, what about some of our listeners said that what if it's both?

Like, what if there's dark matter and the black hole in the center of our galaxy, Like, could it be a mixture of the two things, like some sort of super compact dark matter thing and maybe a black hole or not a black hole or a bunch of neutron stars or something like that? Yeah, it could basically be, you know, all of the above, right? And remember the current theory, the prevailing wisdom is not just that it's only a black hole. We do think that there's a lot of dark matter at the center of the galaxy. We think that's the densest place to find dark matter in our galaxy is at the center. But the current thinking about the density of dark matter is that it's not that great, right?

Dark matter. There's a lot of it in the galaxy, but it's also spread out through space a lot more evenly than normal matter, because again, it doesn't clump. And so for example, in the volume of the earth, we think there's like less than a kilogram of dark matter, like less than one squirrels worth of dark matter. So there is almost certainly some dark matter at the center of the galaxy and almost certainly some dark matter in that black hole if it exists, but it's not contributing significantly because it's not that dense. It's sort of spread out everywhere through the center of the galaxy. Yeah, dark matter is pretty squirrelly and like that.

Hard to catch. But we also see dark matter sort of clumping in our galaxy, right? Like dark matter is not a totally diffused cloud. It does sort of clump in the middle, but you were saying it doesn't clump enough to maybe explain what's going on. Yeah, what we're talking about here is like an enormous spike in density. Yes, dark matter is denser at the center of our galaxy, but this object, whatever it is, with four million times the mass of the sun in a very small area, is much denser than the

typical dark matter density at the center. Yeah, it's 4 million suns, basically, in the space of our solar system. Yeah. That's a lot of ice cream. It's a big scoop. In one place. Yeah, it's a big scoop of stuff. All right, well, it sounds like a black hole is what most people think is at the center

of our galaxy, but there's still a lot of questions about that. And there's even maybe a little bit of uncertainty whether it is a black hole. So what are we doing about it? How are we going to answer this question? Well, we have an awesome new telescope, this event horizon telescope, which is actually you know, like a collection of telescopes that all work together to make an effective telescope like the size of the Earth. And it recently took a picture of a black hole, right? M87, this black hole at the center of a distant galaxy. And that was really cool because you could see essentially

the size of the event horizon. You could see a black circle at the center surrounded by gas and dust that was emitting a lot of light. And that told you essentially the radius of the event horizon because you could see where the light stopped. That's what's really awesome about that picture. So if you could train this same telescope at the center of our galaxy, you'd get a much better measurement of the radius of the event horizon if there is, in fact, a black hole there. And then we could get a clear idea for what's really going on because that's the thing we don't understand very well is like, what is the radius of this thing, whatever it is. Is it big and fluffy like a blob of dark matter or ice cream? Or is it really compact less than a tenth of an AU like a black hole would be? I see.

Yeah, I guess having a picture of another black hole at the center of another galaxy basically says like, hey, this is normal. Like, look, there are black coals at the center of galaxy, so probably ours has one too. Probably. And this is challenging, though, because it's very difficult to take these pictures. And it's harder, in fact, to get the picture of the center of our galaxy than this other distant galaxy. M87, we could just sort of look at the center of it. We're not buried in the galaxy having to look through most of it. We could look at it sort of from the side.

the top, you know, whereas our galaxy, like, we're right in the middle of it. So we had to look through all of this gas and dust to see the center of the galaxy. Right. And M87 also was targeted because it's a huge monster black hole. It's like really enormous. Whereas the black hole of the center of our galaxy, it's big, but it's sort of smaller on the scale of super massive black holes. Right. Yeah. It is it, I guess, closer than this other galaxy, but it's still, you know, like 50,000 light years away, right? Yeah, we're about 26,000. thousand light years from the center of the galaxy, which seems like a lot, right? But astronomically speaking, it's really not that big a number.

Other galaxies are millions of light years away. Yeah. I guess it's closer, but it's smaller and it's dustier. And it's also a dimmer black hole, right? It's a dimmer black hole and there's a more variability. Like the fact that it's smaller means that there's much more like variation in the brightness of this black hole. So it's not as easy to look at it to stitch this picture together.

Now, they've taken the data, like they turned the telescope towards the black hole effectively in 2017. And since then, they've been crunching it through the computers to try to make this picture. So the only thing standing between us and a picture of the black hole at the center of our galaxy is, you know, enough computers. Right. Yeah. We need more computers. But I think even if we do get a picture, sometimes we're not sure if it's a black hole either, right? Like you were saying before, even the picture of the black hole we have in the other galaxy, it might not be a black hole, right? Yeah, there are other ideas for what could be that dense and that gravitationally powerful. You know, in the end, black hole observations are always a little bit indirect

because you can't actually tell if there's an event horizon there or if it's just something that's not emitting and is very, very dense. You know, it's sort of like we have a list of things that can do that and black holes are the only thing on the list. So we assume that whenever we see something that dense, that gravitationally powerful, it must be a black hole. But then people come up with other ideas like dark stars, these very time dilated collapsing stars that could also do that. We don't know if that's a thing in our universe or not.

But in the end, until we go and visit the black hole, we won't know for sure if there really is an event horizon there. Yeah. So back your bags, Daniel. We're sending you. All right. I'll bring my ice cream spoons. Yeah, make it a big scoop. All right.

Well, it's a big mystery at the center of our galaxy. And it sounds like scientists are, you know, leaking away at the data. to get to the juicy candy center. To find out the flavor of truth. Hopefully it tastes like butterscotch or Dulce. It tastes like hard work and a lot of GPUs. Now let's be honest, it just tastes like coffee. That's what physics tastes like.

Yeah, from all the coffee consumed to do it. Chalkboard dust and coffee. That's the flavor of physics right there. Hey, you should come up with a candy for that and sell it. Chalk and coffee. Chaffy. Yeah, it'll be good for your bones. All right, well, stay tuned.

We are slowly but surely looking closer at the center of our galaxy to find out what's at the center of it. And what's inside could tell us a lot about how the galaxy got formed and even how the universe got structured and got to the shape it is today. And we're doing everything we can to try to understand what's out there in the universe from this tiny little rock floating out in space. And every time we build a new kind of eyeball or figure out a new way to look out in the universe, we learn something new about what's out there. Yeah, I just hope we do it before it melts. Well, we hope you enjoyed that. Thanks for joining us. See you next night.

Thanks for listening. And remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. terrorism. Listen to the new season of law and order criminal justice system on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school

week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't Trust her. Now he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. That was diagnosed with cancer on Friday and cancer free the next Friday. No chemo, no radiation, none of that. On a recent episode of Culture Raises Us podcast, I sat down with Warren Campbell, Grammy-winning producer, pastor, and music executive to talk about the beats, the business, and the legacy behind. some of the biggest names in gospel, R&B, and hip-hop.

Professionally, I started at Deadwell Records. From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that drives it. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.