Daniel and Jorge Explain the UniverseDaniel and Jorge talk about the mystery of the missing mysterious black hole at the heart of M33
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All right, hey, Daniel, are you ready to record?
Oh? Wait just a minute, I lost something.
Well what are you looking for? Oh?
You know, nothing important?
This black hole a black hole? How can you use a black hole?
I don't know if it really sucks.
Yeah, you have a massive problem there to be. Your parents teach you to always take care of your black holes.
I seem to just be accreting problems.
Hi am jorham Mack, cartoonist and the author of Oliver's Great Big Universe.
Hi I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I really do want a personal black hole.
Like your own little black hole in your backyard or like in your pocket.
Preferably like in a lab at work, in a basement behind lots of shielding, et cetera. But yeah, I'd love to have a black hole to study.
Wouldn't the shielding fall into the black hole?
You know, if you build a small enough black hole, then it would actually be stable.
Wouldn't it evaporate eventually? Or do you have to keep feeding it?
Yeah? Exactly. You could keep feeding it at just the same rate it was evaporating, and you could keep it there safe and sustainable.
Hmmm, I wonder how stable that would be. It might turn it to runaway process by accident.
Oh yeah, I mean you might accidentally like consume the whole earth, etc. Dot dot dot. But uh, you might learn a lot along the way.
That would be a problem for the rest of us.
You wouldn't worry about it afterwards, I mean, you wouldn't be around.
I'm pretty sure we would learn not to give you a black hole.
Yeah, well, it's a one time mistake.
That's for sure, but anyways, welcome for a podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we tap into your desire to understand the whole universe, your absolutely desperate need to know how the universe actually works. What's out there, how does it function, what rules is it following, what are its fundamental basic bits, and what's controlling all of it? Is there reason and in order to the universe or is it all just a big chaotic swirl?
That's right. We like to talk about everything that's happening in the universe before you lose your mind or any giant gravitational objects out there in space.
I think I'm more likely to lose a black hole than lose my mind.
I think if you own a black hole, you might have already lost your mind. Guilty, or maybe the rest of us lost our minds for letting you have a black hole that might destroy the Earth.
Sometimes I do think people were crazy to give me this job.
But that is an interesting scenario to have, like a personal black hole in a lab to study. But what happens if you have to move labs? How can you move a black hole?
A black hole is just a thing, so you can move it the way you move everything else, you know, But how.
Do you push it? You can't push it, can you? You can't pick it up?
I mean, I wouldn't put your hand in it. But it has massed, so you could attract it with other gravity.
I suppose, I suppose maybe you think about this a little bit more before creating a black hole here on Earth.
I mean, if you have the capacity to create a black hole in a line, but then you could just stop feeding it, let it evaporate away, and then create a new one somewhere else.
But would it be sort of a potentially unstable or are black holes relatively stable, like if a p fill in or a speck of dust? Would it be too much and then suddenly we'll grow out of control.
They're definitely unstable. So you'd be writing the knife's edge between learning something about the universe and destroying all of humanity. It'd be a very delicate balance because, as you're saying, it grows too big, then it has more gravity. Then it can grow bigger faster, and then it'll have even more gravity. Dot dot dot, and there's no way to turn it off.
Yeaha YadA YadA, We all die horrible dead. I don't like this physicist, YadA YadA.
The problem is that there's no way to shrink a black hole except for letting it evaporate, and that's a very slow process. Especially as the black hole gets bigger, it evaporates less and less, so once it starts to run away, there's like no safety valve. There's no like black hole extinguisher you can spray on it.
Hmmm, I guess you can't shoot it with like antimatter.
That wouldn't help, right, antimatter wouldn't just make it stronger. Nuclear weapons just make it stronger. More black holes just make it stronger. Any kind of energy just makes it stronger.
So that's like it'd be a bad idea to try to create black holes here on Earth, right, Like, who would do that? That's insane?
Well, we are literally trying to create black holes at the Large Hadron Collider.
I know that's why I bring it up, But it sounds like a terrible idea.
Think of all we could learn, man.
Yeah, again, we could learn not to trust physicists too experiment with black holes here on.
Earth, maybe, But you know, black holes are such amazing mysteries. We don't know how they form, We don't know what's inside them. We don't know how gravity and relativity come together to make it all make sense, or if he does even make sense, or if behind that veil the universe is like broken and chaotic in some weird way. But the most frustrating thing is that they're all so far away. There are no black holes nearby for us to study.
And that's a bad thing.
That's a bad thing if you want to learn about that.
Yes, I get it. They're very mysterious and interesting. They might potentially unlock the mysteries of the universe. But maybe we should send you there instead of trying to bring them here.
Maybe I'll send the probe, haven't that?
Oh there you go, all right, we'll compromise. But yeah, black holes are super mysterious and as you said, maybe hold the key to the universe. And sometimes they can get lost.
Apparently, maybe some aliens out there are creating black holes and then accidentally losing them.
So today on the podcast, we'll be tagging the question what happened to M thirty three's central black hole? Now, there's a lot of numbers here. M thirty three central black hole? Is that someone's black holes.
I don't know who made that black hole or where they put it or why they lost it. But M thirty three is a galaxy fairly nearby one without a black hole seen at its center?
Is there evidence that it had a black hole before?
There is no evidence that it ever had a black hole, And so that's sort of the question is like, how do you form a galaxy without a black hole? Or did you form it and lose it? How is that even possible? What's going on? M?
So maybe the real question is like, why doesn't M thirty three have a black hole in the middle.
Yeah, that's another way to say it.
It seems like me it's the more great way to say it. Like if I never had a million dollars and I went around asking what happened to my million dollars?
Might get some weird looks with like everybody in your neighborhood wears pants, and then you walk around without pants, people might say, hey, what happened to his pants? And saying hey, I never wore pants isn't really an explanation, all right, Well.
To dig into this interesting mystery, and as usual, Daniel went out there asking people if they knew what happened to M thirty three's central black hole?
Didn't ask anybody if they wear pants. That's a piece of information they can keep to themselves. And you don't have to wear pants to participate in this part of the podcast. It all happens online via email, So if you would like to give answers to future physics questions, please write to me two questions at Danielandjorge dot com whether or not you have a black hole or pants.
So think about it for a second. What do you think happened to M three three's central black hole?
Did something happen to M thirty three central black hole? I don't know. I can only assume that it's either dissipated or it's getting bigger. I don't think you know, because over time, don't they give off hawking radiation? Right, so over galactic periods of time then it would disperse. But you make it sound like it's happened more suddenly than that, because I don't think we'd be able to observe that, because you know, that's over billions of years. So I can maybe assume that something spectacular has happened. Maybe it's like swallowed something huge and it's it's maybe I don't know. The accretion disk is glowing more than it would normally.
I don't know.
Does it get absorbed by another black hole and produce gravitational waves? I'm going to guess something epic happened to it. Did it collapse and disappear?
All right?
Well, now, Daniel, you've made me wonder whether these people that were telling us their answer if they had pants on or not.
That's the detail you're wondering, right, you have no idea what they look like, where they live, But now you're curious about whether they're wearing pants.
Well, I'm wondering if you gave him permission to do it pantless, and whether they followed your instruction.
I mean, I didn't tell them to take off their pants. That would have been kind of weird.
Yeah, what kind of business are you running here? The pantless Business club?
It's pants optional, not pantless. It's very different.
Everyone has to wear kilt.
Where whatever you're like, we don't care.
Wait, are you saying you can be naked? Is this like the clothing optional Physicist club?
Absolutely? Where would ever be like wear nothing? Where everything doesn't matter, it's all online. If it doesn't to get to wear your curiosity. I guess you go wear your curiosity on your sleeve whether or not you can have a sleep.
I feel like you have low standards for your online friends, Daniel.
I'm just focusing on most important.
Like can you tweet? Then you're my friend clothes. I need to know nothing else.
What was that about tweeting?
You just have to tweet. I don't care about anything else about you.
And you think I'm friends with everybody.
On Twitter, Well not everyone on Twitter.
I do like interacting with our listeners on Twitter. If you like being on Twitter, come and tweet us a question. We will answer it.
Well, nobody seemed to have an idea of what happened to this galaxies central black hole. In fact, people seem to be sort of alarm your question. You're like, what, what did something happen.
Exactly? And you're the number one suspect. Do you have an alibi for where you were when this black hole disappeared? I was out buying pants apparently where you were donating all your pants.
It sounds like, yes, I was having a grass cell for all my pants. I was helping you look for your black hole. That's what I was doing.
Story keeps changing pretty ciss.
Well, let's jump right into this, Daniel. So why are we talking about black holes? What are they? And how can we miss them or lose them?
So we talk about black holes a lot on the podcast, and people who listen regularly will know that black holes are this theoretical concept of prediction of general relativity that if you have enough mass or just energy in a localized spot, it will bend space so dramatically that no information will be able to leave past an event horizon. We don't actually know what's going on beyond the event horizon, but general relativity predicts that there's a singularity, a dot of infinitely dense matter curving space so intensely that even photons cannot escape. We've seen black holes out there in the wild, or things we identify with black holes. We can't actually verify that they have this event horizon. But there are some very dense, very massive objects that seem to give off no radiation, and black holes are the most popular suspects to explain those weird dense objects. M.
Yeah, we've talked about this a little bit before that you know, there are pictures online of what physicists think might be black holes, and they look like black holes, right, Like, if you look at these images, they're just black circles. But as you said, maybe these could not be black holes.
Yeah, they actually kind of look like Krispy Kreme donuts because what you're looking at in the image is this halo, this accretion disk, this blob of gas swirling around the black hole at the center of it. You're right, there's this black circle, and they say, oh, that's the black hole. But it's more like an absence of information that tells you something we don't actually know what is. There could be a black hole, it could be a dark star, it could be a fuzzball, it could be lots of other things that don't emit light and are super duper dense.
Now, how do you get a black hole or how would you get a black hole if they existed.
Black Holes out in the universe come in two different varieties, which is kind of weird. There's like the smaller black hole, which forms when a star finishes its life. A star when it's burning, the fusion the radiation puffs it out and keeps it from collapsing gravitationally into a black hole. But when it's done burning, when it's no longer producing that radiation, gravity eventually wins, and if the star had enough stuff to begin with, it collapses into a black hole. These are typically like ten times up to thirty, forty fifty eighty times the mass of our Sun. So we call those stellar black holes, and those sound pretty big, Like eighty times the mass of our Sun is a lot of stuff, but that's actually small compared to the other category of black holes we see out there in the universe.
Right, These are called super massive black holes.
Exactly, and these are only found at the hearts of galaxies, a place where there's a lot of matter already, very very dense. These super massive black holes can be tens of thousands of solar masses up to billions of solar masses, really just incredible concentrations of matter in the universe.
So you have these two kinds of black holes, and is there like small ones kind of and super duper big ones. Is there nothing in between them?
In between? There's this category called intermediate mass black holes, and it's a category with a name, but we don't have any observations there. It's kind of a mystery. We did a podcast a couple of years ago about where are all the intermediate mass black holes. It's part of the mystery of super massive black holes. We don't know how they formed, how they got so big. It'd be interesting to see intermediate mass black holes because they might just be like baby versions of super massive black holes. So it's part of the mystery of how these really really big ones formed, why we don't see them forming, why we don't see intermediate mass ones instead of a whole spectrum. We have these two populations.
Now, the ones we've actually sort of seen are the super massive black hole kind right, and the pictures they found a couple of years ago that they took were of super massive black holes, because we don't have pictures of the smaller black holes, do we.
We don't the images that we're talking about. We only have images of the Milky Way and this messy eighty seven galaxy. Those are the two black holes that we have these images of where you can go online and see a picture of the accretion disk, et cetera. Those are very very difficult to take. Those pictures requires a lot of observation from many different telescopes, all coordinated sort of piece that together over several years, and also requires that the galaxy be like close enough that we can see it, but tilted in just the right way so that we can look at the black hole, etc. So we've only done that for a couple but we have identified super massive black holes in a couple hundred other galaxies, not directly with images, but with other techniques.
Right, that's what I mean. Like the ones that you see in the pictures that are online, those are super massive black holes, right, the two that you mentioned. And we don't actually have pictures of even the small ones. We just know they're out there from their gravity.
That's right. We see them out there because of their gravity. For example, you'll see a star and you'll see it orbiting something invisible, and you can calculate with the mass of that thing is. You can see how close that star gets to it, and that tells you how big it can't be, like that's a limit on the size of the thing. That's how black holes were first discovered, is that we saw these things orbiting what looked like nothing, and then we could deduce the mass of the object and get an idea of the size of it, and from that deduce the existence of the black hole. That's the kind of indirect evidence we have for stellar mass black holes, and we can do the same kind of thing to try to look for super massive black holes and the hearts of galaxies.
Right like, if you see some stars swirling around, but you don't see anything bright in the middle, then you sort of assumed that there is a supermassive black hole there.
Yeah, exactly. And in the case of our own Milky Way, we've pointed telescopes at the heart of the galaxy and gotten a lot of details. We followed individual stars as they come very close to Sagittarius, a star the black hole at the center of our galaxy, and we can measure its mass as those stars swing around because we understand the gravitational effect, and when a cloud of dust passes nearby it, we can see, you know, how big is this thing? How close can you get to it without falling in? It was actually Nobel Prize given in the last few years for these detailed studies of the supermassive black hole the heart of our galaxy. So even before we had that image with a pretty good idea for the mass and the radius of this thing, just by studying the stellar dynamics the stars whizzing around it, from which we're inferring the gravitational effect of that black hole, right.
And you can sort of infer or deduce that it's something super compact and dense, right, Like, that's a really strong gravitational effect around the stars that are swirling around it. But when you look there, you not only not see anything bright, but you also just see kind of the space, the space behind there, right, So whatever's there is super massive and it doesn't take up a lot of.
Room, yeah, exactly. And then you look at your menu of like, well, what out in nature can do that? What can be so massive and so small? And the only sort of widely accepted thing is a black hole. There are other speculative ideas for what might be able to do that we talked about on the podcast other times, dark stars and fuzzballs, that it could potentially also do that, And there are various theories of quantum gravity to predict things. But the black holes these days like the vanilla explanation for what could be doing it.
You mean the chocolate explanation.
The dark chocolate explanation exactly.
But I guess what makes it a better theory than some of these other ideas that you talked about, like why is this one preferred? Why is this one vanilla?
It's vanilla because it doesn't require any new physics. You don't have to add to our theories of physics to explain it. You just have to rely on good old general relativity, which predicts these black holes and very accurately describes their radiation and everything we see from the outside. So from the outside, general relativity works perfectly to describe these objects. It's just when you're wondering about what's inside of it that you might need some new physics theories, some quantum gravity to explain the combination of very intense gravity and very very small objects to account for the quantum nature that we know has to play a role inside these black holes.
Now, that's how we can see the one here in the Milky Way galaxy, the black hole center of our galaxy. But in other galaxies, I mean, they're so far away you can't really see individual stars swirling around, right.
That's right. You can't track individual stars in other galaxies. We don't have telescopes that can do that. But you can build up an idea of the stellar dynamics. The velocities for nearby galaxies. By looking at the general brightness near the center of the galaxy. We can get a sense for the velocity of those stars by looking at their spec like how is the light from those stars red shifted? And piecing it together with a whole lot of computing power, we can get a model for what is the velocity of the stars near the center of the galaxy, and from that we can deduce how massive a black hole has to be there to explain the stellar velocities we see.
Oh interesting, It's like if there are a bunch of stars swirling at the center of a faraway galaxy. You can't see them individual stars, but you can sort of get a far away view of the churn that's happening there in that galaxy, right, Like, if there's a lot of stars moving really fast, then their light is going to be red shifted as the stars move away from you, and blue shift as the stars move towards you. And so the more red and blue light that you see coming from the center of the galaxy means there's a lot of movement going on there.
Exactly. We can tell the difference between a galaxy that has a really fast churn with massive stars and a galaxy, it's more like a lazy river, you know, where things are just like bobbing along slowly and sedately.
So you see galaxy where the center is moving a lot, there's a lot of turn in there, but the center's not super bright. Then there must be something really compact, something really dark in there that is probably a super massive black hole exactly.
And it's very similar to how we infer the existence of dark matter. You know, this is an indirect measurement of mass. You say, well, these things are moving, and therefore there has to be gravity to hold them in place. Why they're not being flung out of the galaxy. The answer is there's some gravity there that's holding it in place, and that gravity should be explained by mass, so we can measure how much mass is needed to explain these stellar motions. This is how dark matter was discovered. We noticed that you couldn't add enough mass throughout the whole galaxy to explain the motion of the stars. And here we're pinpointing the very very center of the galaxy.
Yeah, and so it teams that most galaxies have a super massive black hole in the middle, but not all of them. Some of them seem to be missing their black holes. So let's dig into this mystery for the Galaxy M thirty three. But first let's take a quick break.
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All Right, we're trying to find Daniel's missing black hole. Now, Daniel, can a black hole technically be missing? Like, isn't a hole the missing of something?
There's a chunk of space missing. Every black hole is a missing piece of space.
Well, it's like a hole in your backyard. A hole is the absence of some dirt. So really, how can you be missing the absence of some dirt?
Yeah, it's tempting to think of a black hole as a whole. It's like a missing piece of the universe, and in some sense they are. There's an event horizon there. Whatever is behind it is not really part of our universe because it can't interact with us. On the other hand, it is part of our space because it's bending our space, it's causing distortions, it generates gravitational waves, it changes the trajectories of things that are outside of it. So it's definitely a thing, right, It has an influence on our universe.
I see, it's not a chunk of space that's missing. It's more of a whole, as in like a place where things can fall into and never come out. Yeah, but at the center of it, or in general, it has mass and a position and it can move around. It's a thing.
Yeah, it's a thing. It's something, and they're very powerful, these black holes and the hearts of galaxies. It's hard to really wrap your mind around how massive these things are. Billions of stars all compressed down into tiny areas, and it makes you wonder, like what's going on at the particle level and what it would be like to be there.
M Yeah, it must be pretty intense. To be a near a black hole. But as we're talking about, like how we see them, and so sometimes you can see them from a gravitational effect, but sometimes there are black holes that kind of glow, right.
Yeah, some black holes that we call quasars are actually very very bright if they have a strong magnetic field and they're feeding a lot, like a lot of matter is falling into them. Sometimes not all of that matter actually ends up in the black hole. The magnetic field can tend to spiral them around and then shut them up and down towards the north and south magnetic poles, sort of like the inverse of the Aurora Borealis. There's a bunch of particles coming from space and then spiraling around magnetic fields to the north pole before falling into the planet. These guys spiral along the magnetic field but then get shunted up in these very powerful beams north and south. And so a black hole the center of a galaxy can create these incredibly bright particle jets which you can see from across the galaxy.
M they're super bright, right, they're sort of brighter than the whole galaxy. If it happens to point in your direction.
Exactly they're incredibly bright, so bright that for a long time people didn't even really believe they could be galaxies because they were visibly very bright, and we knew they were very very far away, which means that like at their source, they were mind bogglingly bright. When people first wrote down the numbers and were like, what, this doesn't make sense. How could anything be that bright? It would take an incredible amount of power to accelerate those particles and then shunt them up north and south, and in the end of black hole is the only thing we know that can explain that that has that kind of power.
But you can only see them if they're kind of pointing directly at you, right. It's sort of like a flashlight far away flashlight has pointing at you. Otherwise you're probably not going to see it in the middle of the night.
Yeah, exactly. They need to be pointed at you, and they need to be beaming. Not every super massive black hole out there is a quasar. Quasars are just the ones that happen to be feeding right now and be very hot emitting all these X rays.
What's the percentage of super massive black holes that have quasars?
Quasars turn out to be quite rare. It's a smaller percentage of galaxies. But we don't understand exactly why there's a quasar sometimes and why there isn't, so it's not something we've measured very very well. We haven't seen that many quasars, so we don't have a great handle on the fraction of galaxies that are quasars. What we do know is that quasars were much more common earlier in the universe. Like the quasar epic of the universe seems to be kind of over seems to have peaked like ten billion years ago.
Wait, what quasar's peak? And what happens to them?
Quasar's peak? And then they fade? You know, they're not always blasting this incredible bright light out into the.
Universe, like they're run out of stuff or what like, they.
Just stop being quasars. You know, there's still super massive black holes, but if they're not feeding as actively, then they're not necessarily generating these big beams. The feeding of a black hole is not so simple. As it gets more powerful, the stuff around it gets hot and creates radiation, which pushes away its fuel, and so there's this Eddington limit to how fast a black hole can grow. If it grows too quickly, it can end up starving itself. So there's a lot of complicated dynamics for how black holes grow.
But what it means starving itself, Well.
If you emit a lot of radiation, you can blow away the gas that was sort of like on deck to fall in.
So you can be a quasar that quits and you end up being quiet.
Yeah, quixotically, yeah, exactly. And it could be that like in billion years ago in the universe, there was just more fuel available for these black holes to gobble, and they ate all the easy fuel, and we're no longer making quasars. Like the younger galaxies or the more nearby galaxies, we don't see quasars, and those we mostly see them in the ancient galaxies about ten billion years ago.
Now, does our milk away have a quasar in the middle or is it just the regular super massive black hole.
Our galaxy does not have a quasar in the middle, and it's got a black hole, but it's not like that impressed of a black hole. There are other galaxies with bigger black holes.
Well, as you mentioned, a lot of galaxies have super massive black holes in the middle, but not all of them.
Right, Almost every single big galaxy we've seen has a super massive black hole in it. It's like when you're walking around town, you're pretty sure you're going to see everybody wearing pants or shorts or a skirt or something. It's pretty rare to see somebody pantsless out in public. In the same way, when we look at galaxies, like we almost always find a super massive black hole at their heart.
Mmm, what's the general percentage?
I guess, Well, we've only looked at like a couple of hundred. This is not easy to do. You need to have enough resolving power to see distellar motion and figure that all out. We can't do that for very very far away galaxies. But of the couple hundred that we've looked at, every single one has a super massive black hole at its heart, except one that we think was ejected in a very recent collision of two galaxies. And then M thirty three, which doesn't have a central.
Black Well, we'll get to M three three a little bit later. But I think, as you were saying, and as I think we've talked about it before, it's kind of a big mystery about why so many galaxies have super massive black holes, like where do they come from exactly?
And the heart of the mystery is how they get so massive. It makes sense for there to be a black hole at the center of the galaxy. Stuff falls in, it gets more massive. Eventually you get a black hole that seems obvious, but we don't understand how they get so big. We can build models of galaxy formation. You start with very early massive stars. Some of those collapse, those remnants fall in together and form a dense core at the heart of the galaxy, merging into the seeds of black holes, which then slurp on more and more stuff. But if you do those calculations, you run simulations, you don't get super massive black holes, especially as early as we see them in the universe. When we look back in time and stuff really really far away, we see super massive black holes with a massive a billion stars in galaxies that form just a billion years after the Big Bang. In our calculations, there just isn't enough time for that to happen.
So then, what are some hypotheses about how these super massive black holes form?
There are some crazy ideas, like one idea is that maybe there are primordial black holes. That you don't need black holes to form from dead stars which then fall together, but that during the Big Bang when matter was made, also some black holes were made. Black holes not made of protons and electrons and other kinds of matter, but black holes that were made sort of before matter was matter.
What are they made out of.
They're made out of the pure energy in those quantum fields. We think of protons and electrons, these particles as being the basic building block of matter, but that's only true when the universe is sort of cold and old. When the universe is sort of younger and denser and hotter, there's so much energy in these quantum fields it doesn't really make sense to point at one little isolated blob of that energy and call it a particle. It's so energetic, it's all just sloshing around, and in that period there's definitely enough energy to make black holes. What you need is energy density, and so there are some theories that in the very early universe, before things cooled down enough so you could talk about individual particles, some of that energy was converted into primordial black holes, and if so, they could be around to see the formation of these super massive.
Black holes MM Yeah, I definitely had more energy when I was younger and hotter. Now I'm cold and old. So then what's the scenario, Like you had these primorial black holes very early in the universe, and then those just grew as stuff fell into them.
Yeah, exactly. If you already had a black hole, it could see the formation of a galaxy, and then you wouldn't have to start from just the stars in that galaxy to make your black hole. You're already starting from half a billion solar masses or something, and then there is time to make a billion, two billion, five billion super massive black holes to the hearts these galaxies and like super charges.
I see. The mystery is not like how did they get so big? It's more like how did they get so big so fast?
Yeah, exactly when they were so young.
Like there's enough stuff in each galaxy to make a super massive black hole, given the times the univer has been around, you can't figure out how they actually got that big exactly.
Like if you see a seventeen year old with bulging muscles, you're like, Okay, it must have worked out. If you see like a seven month old with bulging muscles, you're like, something is wrong. Here, what's going on?
Yeah, does sound like a very wrong picture.
Pants are not. You don't want to see like massive biceps on a seven month old.
All right, So that's one crazy idea. There's other crazy ideas that maybe involve dark matter, right.
Yeah, exactly. We know that dark matter plays a big role in the formation of galaxies. So some people wonder if you can make black holes out of that dark matter. Because remember, dark matter is like eighty percent of the matter in the universe. So if you want to make stuff that's massive, like, you know, go for your number one ingredient. The idea is that maybe this dark matter can collapse into a black hole, again, seeding the formation of these super massive black holes so you don't just have to start from stars.
Does that mean that most black holes out there, or most super massive black holes, are made out of maybe eighty percent dark matter.
It's a really good question, and we don't know the answer. We think that dark matter is less likely to collapse into black holes than normal matter because it isn't sticky. It's hard for it to lose its original rotational speed. That's why the dark matter in galaxies tends to be a bigger, puffier halo. You know, all the matter in the galaxy used to be big and puffy and slowly rotating, but then it gradually collapses into smaller, denser objects because it bumps into itself or there's friction, and it slows itself down and falls in towards the center. But dark matter can't do that because it doesn't have those kind of sticky interactions. It can't form big blobs, it can't rub against itself, can't slow down, so it keeps swirling in these big.
Fluffy meaning like dark matter is even invisible to itself.
Yeah, it's not just invisible, it's intangible. It passes through itself, we think. And so there must be some dark matter in black holes, especially the ones at the center of galaxies, because it's inevitable some dark matter particle will hit a black hole or event horizon. But we think that most of the dark matter in the galaxy avoids falling into the central black hole for that reason. But this theory suggests that somehow some of it might have formed an over density the heart of the galaxy and collapsed anyway.
To become a dark matter black hole.
To become a dark matter black hole, which then seeds a super massive black hole.
All right, So most galaxies that we see around us have a super massive black hole. How strong is that correlation?
So every single one except for those two exceptions, does have a super massive black hole. And there's also an interesting connection between the mass of that black hole and what's going on in the rest of the galaxy. The galaxy is this big flat disk usually and then this black hole of the center, but also this is bulge. It's like blob of stars and gas and dust at the center of the galaxy.
Sort of like the egg yulgan of fried egg.
Yeah, exactly. And there tends to be a correlation between the mass of the black hole and the mass of that bulge, like a bigger bulge, bigger black hole, smaller bulge, smaller black hole. And that feels like an important clue because it tells us there's some connection, some correlation between this really tiny but massive speck of the center of the galaxy and what's going on in the rest of the galaxy.
Meaning like if there's just a whole bunch more stuff there, then maybe it's more likely that there is a black hole at the center.
Yes, somehow there must be a process that affects both of them. Either they're interacting in some way, or they're both formed by the same process. The bulge in the black hole definitely seem to be connected. It's not random. It's not like you get huge bulges in tiny black holes, or huge black holes and tiny bulges. So the bulge is giving us some clue about the formation of the black hole, because the process that made the black hole has to also be involved somehow in the process of making the bulge.
Now, how important is a super massive black hole to the structure of that galaxy? Like if our galaxy suddenly somebody plucked the super massive black hole in the middle of our galaxy, would our galaxy look different or spiral out of control or dissipate, or would it pretty much be the same?
It would pretty much be the same. I mean, you would disturb the orbits of stars in the very very center. But even though super massive black holes sound awesome, their mass is really tiny relative to the whole galaxy, much much less than one percent, less than a tenth of a one percent in many cases, and so it's really an irrelevant part of the whole mass budget of the galaxy, which is in the end what controls the dynamics and the structure of the galaxy.
Like to have an impressive name, super massive black holes, but they really don't ender at the center of the galaxy. But that's maybe just incidental. It's not like you need a super massive black holes to have a galaxy.
Yeah, that's right, you don't. But it does seem like they're connected to the center of the galaxy of it, you know, the ball, just some process there that either is connecting them. It's like a feedback mechanism, so as one grows, the other one grows or against some process that leads to both of them. So they do seem to be connected to the center of the galaxy. But yeah, you could delete one or yet it out into space without destroying the galaxy. The galaxy would spin on.
It's not like an essential ingredient in the formation of a galaxy. No, not at all, but it does seem to be maybe not necessary, but it does seem to always be there because of most galaxies that we see Nero, as you're saying, have a super massive black hole.
Yeah, so it seems like an important part of understanding galaxy formation because they seem to almost always be created and to be connected to the rest of the galaxy, and they also might have clues about the expansion of the universe. Remember, like a year ago, there was this paper noticing a correlation between the masses of some of these galaxies and the expansion of the universe, the theory that these supermassive black holes might actually be like bubbles of dark energy, that they could be the things expanding the universe and accelerating that expansion.
WHOA, all right, Well, as you said, there are two galaxies that we know about that don't have super massive black holes in them. So let's stick into why that is. What happened to them? Did someone steal in did a physicist lose them? So let's dig into that. But first let's take another quick break.
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All right, we're asking the question what happened to M thirty three's central black hole? And this is a question because most galaxies seem to have a super massive black hole in them, but not all of them. So Daniel, what happened to their pants?
Well, I think every galaxy except for the triangular galaxy M thirty three, really can be connected to a super massive black hole. Like almost all of them, there's a super massive black hole and it's still in the center. A tiny fraction of them no longer have a super massive black hole, but in those situations you can usually identify what happened. You can see the super massive black hole having been tossed out into space in some crazy three body interaction or a supermassive black hole has like being kicked away from the center of the galaxy, so it's still in the galaxy, but no longer at the core. Except for M thirty three. M thirty three appears to have no super massive black hole currently, and there's no super massive black hole that you can associate with it at all.
So it's just the galaxy out there. And so what happens when you try to look in the middle you don't see any kind of like super quick turning in the middle. Is that how you can tell that it doesn't have a black hole in the middle?
Exactly? It's a lazy river. So this is a galaxy that's two point seven light years away. It's in the constellation Triangulum, so it's sometimes called M thirty three, sometimes called the Triangulum galaxy, and it's a big galaxy. Like in our local group, which is the cluster of galaxies that we live in, there's and Rama, the biggest king galaxy, there's the Milky Way, and then there's M thirty three, so it's the third biggest galaxy sort of in the neighborhood. It's got like sixty billion solar masses total.
Meaning it has the billion stars in them.
No, that's just a unit of mass. That's how you measure the mass of something. It's like if somebody says you're four stone, that doesn't mean you're literally made of four stones. Right. In this case, the galaxy is mostly dark matter. So it definitely doesn't have sixty billion stars. It's got a tiny fraction of that. It's mostly dark matter, but it has enough stars that you can follow their path at the core, you can measure their velocity, and from that you can infer the mass of any black hole that could be at their center.
So this is kind of a small galaxy, right, because our galaxy has a one hundred billion stars.
Yes, this is a smaller galaxy than the Milky Way, but it's big compared to the neighborhood. I mean, our galaxy is one of the bigger ones in the Neighborhoods's Andromeda and then Milky Way ring number two. So this is number three.
And so you're saying, when we look in the middle, we don't see a black hole at the center.
That's right. As you look at the stars, their orbits don't get much faster as you get closer. If there's a really big super massive black hole there. Then its gravity is very powerful and for a star to stay in orbit very close to be going super dup or fast. If there's no central black hole there, then things can just be sort of like putting along near the center without being disturbed. It can survive with slow velocities.
But I guess if this galaxy is that much smaller than ours, could it be that it has a black hole in the middle. It's just not at the super massive level yet.
It could be that there is a black hole there, but they can infer the maximum size a black hole could be to be consistent with the motion of these stars, and it would be a thousand times smaller than the black hole you would expect for a galaxy this size. So either there's no black hole there, or there's a much smaller black hole than we expect to see for a galaxy this size. If this one has a black hole, then it has to be smaller than like fifteen hundred solar masses. That's tiny. That's almost down to the stellar mass black hole level. It's actually right in the intermediate mass black hole region, which is quite interesting.
And so is there anything peculiar about this galaxy? Are there any either about it that might tell you why it doesn't have a black hole?
One other clue is that it doesn't really have a bulge. We were talking earlier about how most galaxies that have really big, massive black holes also have really big bulges. Well, this one's got no black hole or maybe a tiny one, and almost no bulge. So it really suggests that black holes are closely associated with the bulge. Whatever makes the disc is not connected to the black hole, but whatever is making the bulge is deeply connected to the formation of that super massive black hole. So it feels like a clue.
Maybe this galaxy just works out a lot. You know, it doesn't have a.
Bulge, wouldn't that give it a bulge bulging muscles?
Well, it depends on your workout, I guess true. Like if you just run out of a lot, you just slim and trim.
This is a spelt galaxy.
You're saying, yeah, there you go, like a runnery galaxy.
Yeah.
Are there other galaxies that we've seen out there that are this size don't have a bulge, but do have a black hole? Or is there a relationship between bulges and black holes?
This is close relationship between bulges and black holes. Other galaxies roughly the size have bulges and have black holes. This is the only one we've seen without a black hole and also without a significant bulge.
Is it the only one we've seen without a bulge? Yeah, Like, out of the Brazilian galaxies out there, we've only seen one without a bulge.
We see smaller ones with smaller bulges and smaller black holes, but this is the edge of the spectrum. This is the tiniest bulge and tiniest black hole.
Oh.
Interesting, So it's truly unique in the entire universe, or we just haven't seen enough galaxies.
We've definitely not seen enough galaxies. We've looked at thousands of galaxies and measured the massive black holes of hundreds of them. So this is early days. You know. This is the kind of science where you're discovering individual ones and wondering if they're typical or weird. You know. It's like when we were first discovering exoplanets and we didn't know is every planet out there hot Jupiter? Oh, it turns out that's just the first ones we see, because that's what we're good at, and so we haven't seen a whole lot of examples of super massive black holes because it's tricky, right, you have to measure the velocities of stars near the centers of other galaxies. In order to do this kind of measurement, it's hard, so we don't have a lot of data, so there's always going to be an outlier when you have a small sample.
We've seen like maybe billions of galaxies out there. Are you saying we've only studied a few hundred of them.
We've seen zillions and zillions of galaxies. You're right, and James Webb's excellent, and the Hubble Deep field shows us lots and lots of galaxies, but in terms of measuring the super massive black hole, most of those we can't. The only way they do it is for them to be close enough for us to be able to measure the stellar velocities near the heart of the galaxy or to see the quasar from a really, really old galaxy, and that adds up to a few hundred mmm.
So then that's the kind of central mystery of today, which is that you have this galaxy. I'm thirty three Triangulum and it looks like it's a small galaxy, but it's a pretty regular galaxy and it doesn't have a super massive black hole in it.
Yeah, exactly.
The only clue we have is that it doesn't have a bulk.
Exactly, and so it's like never worn pants, you know, it's like happy in its pants. Free existence. Doesn't seem like it had a super massive black hole and lost it, because then they would have a bulge with no black hole. And we don't understand how these things form at all, and so there's this interesting clue by the connection with the bulge and not with the rest of the disc. So as we see more and more of these things, we hope to learn more about how galaxies form and how super massive black holes form. But these exceptions, these outliers, are really important clues because they tell us what rules can be broken, right.
It sort of tells you, like what's necessary and what isn't, Like, you can't have a galaxy without a bulky.
You can have a galaxy without a bulge and without a black hole at its heart. You still get a very nice galaxy.
And you can get a galaxy without pants, and it seems perfectly happy.
I don't recommend doing that, but yeah, it does seem possible.
Dan it will happened to your pants right now? No comment, exactly, it's a mystery.
I lost them in the black hole.
It fell hole that you lost. That's why you're looking for your black hole because it it's running away with your pants.
But without pants on, it can't go outside and look for it. So now I'm stuck.
Oh man, you're gonna have to ask to your friends on Twitter, look for your pants and your black hole.
Go fund me for new pants for Daniel. There you go.
That's what the Internet wasn't there for pants free Fridays? All right, Well, another interesting example of how there is still so much mystery in the universe. Even I feel like this is a mystery wrapped inside of a mystery, because black holes are a mystery. But this is about the missing black hole. So it's like the mystery of the missing mystery.
Yeah, exactly where did the mystery go?
All right? Well, we hope you enjoyed that. Thanks for joining us. See you next time.
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