Modern Wisdom - #536 - Dr Becky Smethurst - The Secret World Of Black Holes

Episode Date: October 8, 2022

Dr Becky Smethurst is an astrophysicist, author, YouTuber and a Junior Research Fellow at the University of Oxford. Black holes are the weirdest, densest, most mysterious objects in the universe. However they're not black, and they're not holes. In fact pretty much everything you think you know about them is probably wrong. Expect to learn why galaxies don't actually orbit black holes, why the biggest black hole in the universe needed an entirely different name, whether black holes can form without neutron stars, what happens when two black holes collide, why nothing can go faster than the speed of light and much more... Sponsors: Get $100 off plus an extra 15% discount on Qualia Mind at https://neurohacker.com/modernwisdom (use code MW15) Get a Free Sample Pack of all LMNT Flavours at https://www.drinklmnt.com/modernwisdom (discount automatically applied) Our Sponsor LetsGetChecked - get 25% discount on your at-home testosterone test at https://trylgc.com/wisdom (use code: WISDOM25) Extra Stuff: Buy Dr Becky's book - https://amzn.to/3SLqnZJ Follow Dr Becky on YouTube - https://www.youtube.com/c/DrBecky  Get my free Reading List of 100 books to read before you die → https://chriswillx.com/books/ To support me on Patreon (thank you): https://www.patreon.com/modernwisdom - Get in touch. Instagram: https://www.instagram.com/chriswillx Twitter: https://www.twitter.com/chriswillx YouTube: https://www.youtube.com/modernwisdompodcast Email: https://chriswillx.com/contact/  Learn more about your ad choices. Visit megaphone.fm/adchoices

Hello friends, welcome back to the show. My guest today is Dr. Becky Smedest. She's an astrophysicist, author, YouTuber, and a junior research fellow at the University of Oxford. Black holes are the weirdest, densest, most mysterious objects in the universe. However, they're not black and they're not holes. In fact, pretty much everything you know about them is probably wrong. Expect to learn why galaxies don't actually orbit black holes. Why the biggest backhole

in the universe needed an entirely different name? Whether black holes can form without neutron stars, what happens when two black holes collide? Why nothing can go faster than the speed of light and much more. But now, ladies and gentlemen, please welcome Dr. Becky Smedest. What is your problem with the name black holes? This is a thing. Something I spent my entire life trying to understand, and yet I hate the name for them. I hate it so much.

I don't think there's any other words in physics that have caused more misconceptions than black holes, because they are neither black, nor are they holes, black holes. And this is what bugs me about them. So people picture a black hole as this physical hole in space that stuff is like lost down. You know, people ask me questions like,

what's on the other side of a black hole? Which doesn't make any sense when you realize that black holes aren't holes. They are 3D objects that were one stars that have just been crushed down until they are so, so dense that the gravity is so strong that nothing can escape it from them anymore, not even light. They're almost like prisons for light and I often say that a better name for them is probably dark star, but even that's not not perfect either. So I mean, I'm sure a lot of listeners could probably come up with their own names for them, but Black Hole especially is one that just if I could go back and be like, no, let's not call it that back to the

sort of 60s and 70s, I would. Who was the guy that called them Black Holes? What was the story with that? Yeah, so it comes from a bit of a harrowing part of history actually. Are you familiar with the black hole of Calcutta? No. So the black hole of Calcutta is a prison cell in an old Fort William in Calcutta in India. And there is this sort of tale from history where British soldiers were imprisoned in this prison cell which was the size of three double beds. And there was about 70 soldiers imprisoned overnight in this one very cramped tight space. And historians sort of claims estimate, you know, that around about 20 of them actually survived

that one single night after being imprisoned in this such incredibly cramped quarters. And there was a physicist called Robert Dickie in the 60s who was studying what then were known as gravitationally completely collapsed objects or GCCOs, which again as a term I'm quite glad that didn't stick. And him and his family used to say that, you know, if something was lost in their house, oh, it's gone to the black hole of Calcutta. And so he started to use this phrase, you know, in his academic talks, as sort of, you know, as like, almost like brevity and advertising value, essentially, it was how it was described by the physicist, called Wheeler as well. And essentially he compared

the crush of matter down to the crush of these soldiers in this prison cell as well in the Black Hole of Calcutta. And I think when people hear about the Black Hole of Calcutta there's those memorials still in Calcutta and India today, they think that the prison got its name from the astronomical objects, but in fact, it's the other way around, which I think people don't realize. What would happen as you move around a black hole? So I think when people think about a black hole, they think about kind of a two-dimensional object, and if you were to go side onto it, that what's on the other side, you look at it from behind, what is it like if you were to orbit around it? Is it a sphere? Yeah, it's just spheres,

probably the best way of putting it. So, I mean, there were one stars. Stars is spherical, so that's like saying, you know, what's on the other side of the Sun? It's just, you're still looking at the Sun. Or the Sun, yeah. Or the Sun, yeah. So it's the same with black holes.

And if you could sort of orbit one very safely and see what was going on, what you would essentially see is this sphere of darkness where no light was coming from it at all. You were receiving no information, nothing. And the edge of that sphere is what we call the event horizon. You might have heard that term before, this sort of point of no return, where nothing can escape the black hole anymore, because you can't travel faster than the speed of light. That's sort of a no-lure physics. If it's a dark sphere, what's your problem with the word black then? So the other issue that I have with black is that not all black holes are dark.

In fact, black holes are some of the brightest objects in the entire universe. They lie up like Christmas trees. And that's because as gas comes into a black hole and spirals around it, beyond the event horizon where we can still see that gas, it gets accelerated to huge speeds by the gravity of the black hole and it gets hot. And just like, you know, if you stick an iron poker in a forged fire, right, and the iron starts to glow because it gets hot, this gas starts to glow in x-rays and UV light and even visible light that you can see with your own eyes as well. And so most black holes from,

you know, what we call stellar mass black holes that are formed in supernova when stars die and we find them across our entire galaxy, you know, there's probably millions to billions of black holes in our entire galaxy right now that are somewhere around like 10 times the mass of the sun, something like that. They all light up so that you see them peppering the night sky. If you look at the night sky with say an x-ray telescope, they light up and you see them there. But not only that, super massive black holes that we think live in the center of every single galaxy, every island of stars in the universe, of these trillion stars, there's this supermassive black hole in the middle that's say a million to a billion times the mass of the Sun. Those things can have so

much gas around them that they're so bright that they can outshine all the stars in their galaxies. To the point where, before we launched the Hubble Space Telescope, we detected the X-ray light from these supermassive black holes and didn't know what they were. And we essentially dubbed them, I say we, I wasn't around at this point, but essentially astronomers dubbed them, quasi-stellar objects, quasi-stellar, looks a bit like a star.

And that eventually got shortened to quasar. And when the Hubble Space Telescope got launched, realized that these points of light that we were seeing in the X-ray, they were actually entire galaxies. But it took the Hubble Space Telescope being launched to realize there are entire galaxies billions of light years away that we weren't able to see the starlight from, but we could see the x-ray light from the quasar, the growing supermassive black hole in the very center of them. And yet we didn't know what they were at the time when they were first spotted. Do supermassive black holes and normal black holes do they spin? Or is that neutron stars

that have a spin and do some wild stuff? So neutron stars have a spin? Yes, and they do do wild stuff. And if they have magnetic fields, they can send off these big beams of radiation like a lighthouse. And I say a neutron star is kind of like the baby sibling of a black hole or for all the Pokemon phones out there. The black hole that never was. Yeah, it's not quite, yeah, the Pokemon finds out there of neutron star is a Pikachu to a black hole's right to, right? It's the, a black hole is the next stage of evolution for a neutron star. If you add enough stuff to a neutron star,

it eventually becomes a black hole. And so yes, black holes do spin because they start life as either stars or neutron stars, if the star wasn't quite heavy enough to become a black hole, but that neutron star could grow and grow until it did become one. And you really can't shake off that spin that stars have. So the sun is spinning, neutron stars are spinning, and black holes also remain spinning as

well. And also as you add more stuff to them, and that comes in swirling around them, that adds more of what we call angular momentum, sort of like rotational energy to make them spin faster as well. So, spinning black core is definitely something that we see in the universe when we observe them. And that was really clear in, did you see the event horizon telescope image of the black core in the center of our Milky Way that was released back in May of this year 2022? No, is that a James back in May of this year, 2022. No, is that a James Webb thing or not?

No, this is the event horizon telescope. So to jog your memory, it looks like a big orange donut. I feel like people go, oh, yeah, the big orange donut image, what I say this. And that image was was really quite blurred. And the reason it was blurred was because, you know, we were taking an image for a couple of hours, trying to collect as much light as possible. You know, imagine sort of like a night mode shot on your phone, you do 10 seconds, right,

to let in all the light. This was a few hours. And in that time, the black hole had been spinning. And so the material around it that you were capturing the image of was moving. And so you ended up with a slightly blurred it's like you blurred orange donut image. And that was one of the questions I got when that image came out was, I isn't blurred. Like surely we should be able to get a nice crisp picture. Exactly. Yeah. So you have the opportunity, there's multiple ways that a black hole could form. You have a large star that collapses in on itself when

it's known you've got the energy to continue to support or to stop gravity from pushing it in. But another one is a neutron star, which is pretty big star, condense it down, but then accumulates more matter over time, just as when the formations of planets and stars originally happened, it's just gravity's bringing stuff in. That must be a very interesting way to form a black hole because it's, there has to be a point at which it's the straw that broke the camel's back.

It's the piece of matter that created the black hole from the neutron star. That seems like quite a unique way to create one. Exactly that. Yeah, so that limit that you were just talking about is called the Tolman Oppenheimer-Volkoff limit. So Oppenheimer might be a name that some people recognize from the Manhattan project, nuclear bombs, the reason he was brought onto that project was because he was a nuclear physicist studying neutrons and neutron stars. And so that limit is actually incredibly informative if you

can measure what that is, like what's the maximum mass of a neutron star or the minimum mass of a black hole, he will formed in that way. And there's loads of different ways you can get at it. You can survey the neutron star population and say, let's see if we can observe all the neutron stars, how big are they, how massive, the sort of edge of that distribution will tell us. But also we've recently started detecting what's known as gravitational waves, which are literal ripples in space itself from this cataclysmic merger of, say, two neutron stars that can also form a black hole. And again, that kind of a limit of when do you cross over that point? When have you added too much matter and the straw that's broken the camel's back to make it a black hole. We think that's around

three-ish times the mass of the sun, but drilling that down to is it three point two, is it three point one, is it three point one one five, you know, getting it that is quite difficult. And you can get it in terms of like modeling what neutrons do and how neutrons behave and literally how can they be arranged in this almost perfect crystal? Like a neutron star is essentially this perfect crystal of neutrons arranged as tightly as they can go. You know, the physics of our understanding of neutrons that we can actually look at in the lab how they behave. We can then work out okay mathematically what would be the limit and is that model right or is there some bit of physics that we've forgotten here that we get from our observations? of physics that we've forgotten here that we get from our observations. What is the form of matter that's in a black hole then? If a neutron star is

neutrons pushed together in this perfect form of a crystal, which is as dense as we could possibly imagine, theoretically as we could, what would that can't be as dense as it could be because there's something denser than that than that a black hole? Exactly. And unfortunately that's one of those questions that we don't know. And under the laws of physics, as we understand them, we will probably never know. It's one of those frustrating things as a scientist, like we're taught to ask so many questions,

and it's like the one thing that we almost can't answer. So inside that event horizon, where it's sort of that shroud that you're no longer receiving any light, so there's no information. So you have no idea what's going on inside that sphere of darkness, essentially. There could be some exotic form of matter that we don't know that exists yet, because we can never recreate that on Earth in a lab, because we don't have the ability to make

anything that dense, but also you'd never be able to observe it, because you can never recreate that on earth in a lamb because we don't have the ability to make anything that dense, but also you'd never be able to observe it because you could never get light from it because it would be this form of matter that was so dense as to create this event horizon in a black hole. Or it could be that there is no form of matter that can resist collapsing down completely and you end up with how we describe a black hole mathematically, which is a singularity. So that might be a phrase that people have heard of before, essentially means all your matter is compressed into an infinitely dense, infinitesimally small point that's undefineable in space in terms of how strong the gravity is there. Mathematically, what happens is you end up trying to divide by zero, which I think, if you remember the film Mean Girls with Lindsay Lohan,

the answer to that is the limit does not exist. So it's something that you can't do in math and mathically, it's divided by zero, you end up essentially going to infinity, if you're trying to divide by zero. And so that's how we describe the mathematically, but whether that's actually truly the physics of what's going on inside that shroud of darkness in the event horizon, we don't know. I would love to know, but we don't. Given the fact that there are varying sizes from black hole to supermassive black hole,

it would suggest that it can't be uniform, that the variation in the size of the black holes is due to something that's going on, so that infinitesimally small might be slightly less infinitesimally small and bigger black holes, I don't know. No, not necessarily, so even if a black hole is 10 times the mass of the sun or 10 million times the mass of the sun, the maths still describes them as this singularity. Where everything, 10 times the mass of the sun or 10 million times the mass of the sun is compressed into this infinitesimally small point. But again, that's the maths. It's not necessarily an observation that we've made in terms of astronomy or astrophysics. And I am an observer, I use telescopes, so really that's what I'm always gonna want,

but under the laws of physics, we understand them, we're probably never gonna be able to observe that, so we do have to fall back on the maths necessarily of how we describe them. But it's interesting, you say, you have this always distribution of these masses because we do see this sort of distribution of what I call normal black holes.

You piddly ones that sit in the galaxy, you know, form from the death of stars 10 times the mass of the sun up to say, say, 100 or so times the mass of the sun. And then supermassive black holes which go from a million up to tens of billion times the mass of the sun. And we just have this dearth of things in the middle. We've never found anything between a hundred to a million or so times the mass of the sun. They're called intermediate mass black holes and they're considered almost like the missing piece of the puzzle, like sort of like the missing gap almost because if you think about well how did supermassive black holes become so supermassive,

if the only process we know to create a black hole comes from a supernova, which forms something like, you know, that star mass, like 10 times the mass of the sun, you've got to then grow that to become super massive. So you'd think if these black holes were growing all the time to become super masses, you'd see something in the middle, but we don't. So it's a very interesting problem in astrophysics

about why we don't see things of that mass. Has all the growth already happened of supermassive black holes yet? But then why don't we see them in the early universe as well? And that's one question we're hoping maybe James, the James Webb Space Telescope, will be able to help answer as well as it looks back further and further to things at greater distance, which are also the light has taken longer to get to us. So we're seeing the universe as it was billions of years ago. Your best models at the moment suggest that there is a supermassive black hole at the centre of every galaxy. Are there any galaxies that don't have supermassive black holes in the

middle? Yeah, so the working hypothesis is that every single one does. There are a few candidates where there is speculation about whether there might not be. And that is usually in the case of what we call dwarf galaxies. So for those in who've been to the southern hemisphere or who live in the southern hemisphere, you'll know what I'm talking about when I say the large Magellanic Cloud, which is a little dwarf galaxy to the Milky Way that's in orbit around us. And you can see it from the southern hemisphere is this little patch on the sky of Way that's in orbit around us and you can see it from the Southern Hemisphere is this little patch on the sky of stars that are much denser and there's sort of gas around it if you crack a camera or a camera phone or something like that,

you can snap it with. And something like that, there's still debate about, okay, well, maybe do they have these intermediate mass black holes in the center because we know that galaxy mass and black hole mass are correlated. So if they're smaller in size and mass, they should have smaller black holes in the center because we know that galaxy mass and black hole mass are correlated. So if they're smaller in size and mass, they should have smaller black holes. So perhaps maybe that's something where we'll find them as well. But there are some candidates where we observe the galaxy and the orbit of the stars suggest there is nothing in the center. In which case, well, why? And how?

How did they almost escape getting a super massive black hole? And if that can happen, then how did all the other galaxies that we see having super massive black holes in the center end up with one? There's lots of different questions. And I think people are surprised when we say there is actually that much that we don't know still. But black holes, studies and super massive black holes,

studies especially is still such a young science actually that much that we don't know still. But black holes, studies and superclassicals, studies especially is still such a young science that's only been going for probably about 20 years or so. I mean, back in the 90s, black holes were still called massive dark objects because we didn't quite know what they were, these supermassive black holes were. And it was only sort of with the observations of the center of the Milky Way and the stars orbiting around the very, very center, that we were looked at with the Keck Space Telescopes of Mount Achaea in Hawaii. They look in the infrared so they can sort of peer through the dust that's towards the center of the Milky Way and see the actual positions of the stars and track

them over like 15 years. One of these stars has made a whole orbit in that time in just about 12 years, I think. And from that, you can then work out how fast they're orbiting the thing in the middle, you can work out, okay, how big is the thing in the middle? And you work out that it's about four million times the mass of the sun in an area small in the solar system. And for a while, people were like, maybe it's a swarm of black holes

because these smaller black holes were known. They've been seen as these little x-ray points of light all over the sky, but super massive black holes weren known, and they've been seen as these little x-ray points of light all over the sky, but super massive black holes weren't thought to be real necessarily. So people considered the idea of a swarm of black holes, which I almost wish was real. I just thought of this sort of like beehive

of black holes almost just swarming around, but in fact that would be really unstable. You'd have things sort of like sling-shocking around each other and being pinged out all the time. And so instead, this idea of yeah yeah, a supermassive black hole. And since you've finally been able to get a picture of one with the event horizon telescope as well, it's confirmed that idea that it is one supermassive black hole. Supermassive black holes in the middle of almost all galaxies.

All of the galaxies are around the point in the middle where the black hole is. Does that mean that the black hole is what's holding the galaxy together? Or is it the fact that black holes end up at the centre of galaxies and the rest of the gravity from that matter just holds itself together? Yeah, so that's a really big question that we have in astrophysics. Like what comes first, the galaxy of the black hole? It's kind of like the astrophysics chicken of the egg, essentially. Like, do you have a galaxy of stars? One goes super and over, become a black hole.

It happens to stink to the middle and the whole thing forms around it. Or do you have like a cloud of gas in the early universe that just directly collapse into a black hole and then stars sort of a shepherd didn't form around that. That's also one of the questions we're hoping that James' face telescope will answer because it's been designed to look back to the first stars and first galaxies forming. But that idea of taking a black hole out of the center of the galaxy with the galaxy fly apart. Because if you did the same thing in the solar system, if you took the sun out of the center of the solar system, the sun is 99.99% of all the mass in the solar system. Take it out and all the planets would just fly off the whole thing would completely disperse

and fall apart. In a galaxy, the black hole is not even 1% of the entire mass of the galaxy. The galaxy always outweighs the supermassive black hole in the center. And so if you removed it, nothing would actually happen to the galaxy. It would actually hold itself together under what's known as self-gravity. And when you actually stop to think about this, this is the reason we have a galaxy of stars in the first place and not just a big disc of gas just slowly fueling the black hole over billions of years, because essentially what it means is that the gravity that is in this region of space that we're in in terms of the sun, the gravity is sort of stronger like holding the earth

around the sun than it is the gravity pulling towards the black hole in the center, or even holding the sun together in the first place. And so that self-gravity, the galaxy, is enough to stop everything from falling into the black hole. And it's why I tell people, you don't need to worry, right? Everything just orbits black holes. And we'll happily continue to do that

in the same way that the earth will happily orbit the sun. Like, as long as you don't panic at night, that the earth is gonna fall into the sun. I mean, you don't't panic, you know, at night, the earth is going to fall into the sun. I mean, you don't need to panic about falling into a black hole either. What is the biggest black hole that's been found so far? So it's got a rather uninspiring name, the biggest black hole found. It's called T-O-N-618. You know, recommendations for what we can rename it are much appreciated. recommendations for what we can rename it, I'm much appreciated. The supermassive black hole at the center of that galaxy is close to 70 billion times the mass of the sun, which

we basically had to give it a new name. It had to become ultramassive black hole at that point because that is just right on the edge of what we think is possible. And actually reaching the point that we think might be the maximum mass that a black hole can grow to a tall. Why would there be a maximum mass? Yeah, so it's because of this idea of self-gravity again. If you've got this disc of gas spiling around the black hole, then at some point as the black hole grows, you sort of push out what's called the

innermost stable circular orbit. And so that's essentially the last point that you can get something orbiting safely before it, you know, it can't hold itself up and it will fall into the black hole and it will spiral in. And essentially what happens is that, that moves so far beyond the event horizon that you can get a disc of gas around the black hole and it will never fall into the black hole in the future. Would that mean that you would end up with a band of no man's land in between the material and the black hole? Exactly, yeah, you would have this no man's land where

if something did happen to fall into there, like say there was a passing gas cloud or you know you chucked an asteroid in there or something like that, then if it hit snowman's land, yes, it would fall into the black hole. Or if it merged with another black hole that came in, then it could grow. But the usual way that black holes grow is by what we call accretion, which is from this gas that's spiraling around the black hole. And essentially, what you've got to do is you've got to remove energy from that gas. So if you think about it in terms of molecules with energy that are all pinging around,

and they've got enough energy to keep them on an orbit. But if they collide with another molecule, it's like a game of pool or snooker. You hit the cue ball into it, another ball, and the cue ball stops, and the other one goes flying. So if that kind of collision happens, where one of these molecules stops, all of a sudden that disrupts that orbit and it can fall in because that pull

of gravity from the black hole then pull it in. But if you've got a case where you've got this no man's land in the middle where even if it lost enough energy, it still wouldn't fall into the black hole because it's far enough away that it could always still escape even if it had lost a lot of energy in a collision or something like that, which is amazing to think of that. I think we could be living through this era of really reaching this epoch of the maximum mass black holes could grow to in the universe with finding this T-O-N-618, super massive black hole, sorry, ultra massive black hole at the center of this galaxy, I mean, it kind of gives me goosebumps. Like, I don't know whether to be excited or disappointed that we're living through

the era that black holes could be reaching their maximum. Why is IC-1101 not the universe which has got the biggest black hole at the center of it given that it's the biggest galaxy that we found So It's interesting because there is the correlation there So if you put galaxy mass and you plot black hole mass the two are correlated But it's not a perfect correlation

There's always some scatter that depends on what's happened in the universe's history There's always some scatter that depends on what's happened in the universe's history in terms of to that galaxy. Has it merged with other galaxies? In which case it's probably merged its supermassive black hole in the center. Was there some interaction in the galaxy that sort of pulled on all the gas and stars in it that happens to send gas tumbling towards the center? That kind of thing, every galaxy has an individual history. So perhaps for that one, you know, maybe it's merged a lot of times, but the black holes haven't merged yet. So maybe we're recording more mass, but in terms of stars, but we're not recording in the supermassive black hole yet. Maybe in T.O.N. 618, it just got really lucky in terms

of the galaxy managed to feed it by itself to grow it that big, even if the galaxy didn't get any bigger as well. So there's all sorts of different reasons that just very complex histories. You know, these things have had 13.8 billion years to evolve, right? There's a lot that can happen in that time. You've just mentioned there that two black holes could meet. Two super massive black holes could meet. What happens then?

What's what's that event like? We don't know, we've never observed an event like that. So we do have the LIGO experiment and the Virgo experiment on Earth right now that are detecting gravitational waves from the stellar mass black holes that are formed from supernova. Those are in our own galaxy that emerging together.

So I mean by gravitational wave, if we picture sort of gravity like how Einstein did where he said, you know, if you have a massive curve space, so imagine taking like a football, chucking it on the center of a trampoline, and then you know like rolling like a ping pong ball around it, that would be sort of the equivalent of what mass does to space. And if you imagine taking that football and having two footballs and bouncing them on that trampoline, you imagine taking that football and having two footballs and bouncing them on that trampoline, you imagine the trampoline is obviously under a lot of stress. And so when two black holes are coming together and merging, they're spiraling around each other incredible speeds and curving and uncurving space as they go past to extreme amounts. And so they

send ripples out into space when this happens. and the biggest of those ripples happens when they finally come together and merge. And we actually are able to detect that here on the ground, on Earth. We literally watch the distance between two mirrors where you've got a laser firing back and forth, measuring the distance between them very, very accurately, change by, you know, less than the width of an atom. We see that and we can detect that, okay, well, something just merged in the universe over there. With a supermassive black hole, it's a different frequency of wave that you get. And so what we have to do is we have to build bigger and bigger detectors. That distance between the two mirrors has to increase for us to be able to detect that. To the point where you would need it bigger than the entire earth,

which is insane, right? But there is a plan to do that. There is a plan, it's called the Lisa Observatory, and we're hoping to maybe launch it in sort of the 2030s, 2040s, probably more likely. And it would literally be these three sort of spacecraft in space in a triangle that would sort of trail the earth in its orbit, kept in one of these, what's known as sort of a gravitational stable point, just like what the James Webb Space Telescope's currently at as well. And they would stay there and they would essentially have the system of firing a laser back and forth to detect the distance between the two mirrors and if it changes, you know, a gravitational wave has gone past. So hopefully I can answer a question maybe in 2040 or so we can say this is what happens when two supermassive black holes merge, but you can imagine it's probably a very cataclysmic event when it does happen. I read the five stages of the universe,

which was a book recommended to me ages ago. I had to get it on self print on Amazon. Anyway, it talks a lot about the different stages that the universe will go through, and that a period of just black holes will take up an awful lot of the future of the universe and then very, very slowly due to Hawking radiation. Yes.

Yes. And they will evaporate over time. How long... Why is it that black holes lose their mass? How long does it take? What's talking radiation? Yeah, I mean, you've really gone for literally the most difficult questions we could ever ask. So obviously this sort of situation that you would have for the end of the universe of being black holes and them having enough time to evaporate means that the universe is probably just going to keep expanding forever

or reaches a happy medium and stops. The other option is that it starts to contract again. We still don't know quite know which one of those is actually going to happen. We have some sort of ways of testing which one that would be but sort of on the fence still. But if it was to expound forever and yes everything eventually might become part of a black hole or starts start to die off and slowly accrete stuff around them. If everything then was a black hole, as stars start to die off and silly a creak stuff around them. If everything then was a black hole, they could indeed evaporate, but it would take, I mean, a supermassive black hole would probably be like a Google number of years, right? 10 to the power of a hundred,

which is an incredibly large number. And Hawking radiation is a strange thing that Hawking worked on because he was obsessed with this idea of entropy. I don't know if you've ever heard this term in physics before. Essentially, the law of physics that says entropy cannot decrease. An entropy is almost like a measure of the disorder of the universe. But really, I mean, what it means is that the most likely thing that's going to happen, it's going to happen. So like, if I had a nice warm mug of tea in front of me right now,

that's a nice ordered system, because all of the heat is in the tea, and the air around it is cooler. But we know what will happen, is that the heat will disperse, and it will warm the air around it, and everything will get more disordered, essentially, rather than having a hot tea and cold tea or it will be mixed about. And so, how can we success with this idea of this?

This was a law of physics that had been known for a very long time for hundreds of years. It was a law of thermodynamics, as it's called. And black holes seem to break this. Because if you're trapping matter and energy and light in a black hole, you are removing disorder from the universe and making it more ordered, almost like someone organizing things and being like this all lives here and this all lives here. You're making something so much more ordered. And so he was obsessed with this

idea and trying to reconcile the theory around black holes and thermodynamics. And eventually he sort of came up with a very theoretical description that goes into very much of the quantum mechanics and what's going on in terms of like vacuum energy of the universe. Essentially if you form a black hole, you disrupt some of the quantum signatures that are going through space. So these are sort of very tiny sort of the quantum realm we're talking about. The physics of the very very small sort of particles, what energy just space itself actually has. So by creating a black hole, you disrupt that.

And from the surface, you then could have some of that disrupted energy escaping as Hawking radiation. And so this would mean that actually you are putting disorder back into the universe in that respect. The thing is, is incredibly unlikely that that happens. The same with anything in quantum mechanics, right? There is a very strange probabilistic aspect to it that says, you know, like the edge of the table that's in front of me right now, there is a very vanishingly small probability

that that edge of that table is not there because the atoms that make it up could be halfway across the universe. In quantum mechanics, that is true, that is a true statement. And so, Hawking radiation while the maths checks out, the time it would take for that to happen is ridiculously long. Even what we call a primordial black hole that might have formed in the early universe that might be less than the mass of the earth even, that still wouldn't have had enough time to evaporate by now in 13.8 billion years and put its energy back out into space.

And it's never something we've ever observed either. We should be able to observe it. It would be given off in what's known as gamma rays from the highest energy form of light. We do have gamma ray telescopes looking at the sky, like supernova and things like this give off gamma rays. But we've never spotted anything that looks like Hawking radiation before. And like I said before, I use telescopes.

I'm an observer. I like to have the observational evidence before, you know, sort of saying this is a real thing. So Hawking radiation is still a hypothetical concept. I learned a little while ago, something interesting about the speed of light. So nothing can go faster than the speed of light is something that everybody hears about. I heard, correct me if I'm wrong, that there is a speed limit in the universe and that the speed of light happens to go at that speed limit, not that the upper bound of the speed

that the universe moves at at its maximum velocity is determined by light is exactly that's correct. Yeah, it just so happens to be that light moves at the the speed limit of what we have in physics and it comes from I mean Einstein's theory of general relativity and special relativity you know marries this beautifully and shows why this is the case but essentially as you get closer to the speed of light, things start to act very differently than what they do here on earth and what we call non-relativistic speeds, normal everyday speeds. If you are running somewhere, you're jogging pace,

maybe you start to put more energy in, you increase the speed that you jog at. And that's the same truth for a car, right? You push the accelerator, you burn more fuel, you put my energy in, you start to go faster. As you approach the speed of light, you put more energy in, and all of a sudden it doesn't start increasing your velocity.

It starts to increase your momentum instead, and your momentum is sort of like, how difficult it is to stop you moving. So we have momentum on the ground here as well and we calculate that as mass times velocity. But if it's not the velocity that increases then, but the momentum still increases, it means your mass increases. So as you travel fast at the speed of light, you you put more energy in, you don't get any faster instead, your mass just keeps going up and up and up and up and up to infinity. And so there's almost, again, this get any faster instead, your mass just keeps going up and up and up

and up to infinity. And so there's almost, again, this limit does not exist, right? You get this, this limit where nothing can go faster than the speed of light. It just gets heavier. Just gets heavier, yeah. That's interesting. Okay. What is the short child radius? This watch child radius is the event horizon, essentially. So that's fear around the black hole where you don't get any information from. And Schwarz child was, I mean, an incredible physicist. So I mean Einstein put out his theory of general relativity, smack bang in the middle of World War I in 1916.

And Schwarz child was on was on one of the fronts, one of the German fronts, I think was the Eastern front. And he shouldn't have been there, he volunteered essentially, he was too old at the time, but he was like, no, I still volunteer, despite having a lot of medical problems as well. And he unfortunately died about a year or so after Einstein put out his theory of general relativity.

In that time though, he was fighting on the Eastern front and wrote three, maybe four physics papers on Einstein's theory of general relativity, wrote a load of letters back and forth that Einstein being like, I found this solution. In the trenches. In the trenches. Yeah.

And unfortunately then, and literally after that, passed away, very young, I think, in the trenches. In the trenches. Yeah. And unfortunately, then, and and literally after that, you know, passed away, very young, I think it was in it, it's early 40s. And essentially what he derived was this idea of what happens if your mass is all sort of contained in this sort of sphere. And he was sort of doing it in terms of like a star, right? It was sort of if you have a spherical object and you work in what's

called, you know, spherical coordinates. So you work in instead of x, y, z, so up, down, forward, back, left, right? You work in sort of how big is your circle? How far round your circle are you? And have our round the other side of the circle are you? Essentially. And he worked out for those kind of coordinates which Einstein hadn't done and if you look at that solution you get this what we call a singularity where essentially r equals zero the very middle you cannot define the strength of gravity at that point and it's what's been come to known as the singularity but there's another singularity that occurs,

which is that the Schwarchild radius, which depends on how heavy the thing is, which for a normal star, the Schwarchild radius is well in with that inside the star, it's nothing to worry about, you know, whatever. Because it's not a real singularity like the one in the middle, it just comes about because of the fact that you work in,

you know, these spherical coordinates instead. But what it defines is that what people didn't realize at the time, because this was back in the 1910s, right? And black holes weren't really even theoretical curiosities until the 50s and 60s. What people realized eventually was that that Schwarzschild radius was the event horizon, that point of no return, where you can't literally see anything over the horizon anymore. Is it not a paradox a little bit that nothing can move faster than the speed of light,

but that something can have enough gravitational pull to be stronger than the speed of light? I don't think it's a paradox necessarily. No, because the paradox was to suggest that there is something broken in there. But it would just suggest that there's this law of physics that says nothing can escape from it if you have to be traveling faster than that speed limit of the universe. It's a paradox necessarily. I just think it's a really interesting quirk of nature.

Yes. I mean, it's a paradox necessarily. I just think it's a really interesting quirk of nature. Yes, I guess it depends on how you see the movement of light versus the effect of gravity, because I got it in my head that it's kind of like somebody running on a treadmill, you know, and it's like in order for something to not be able to go that way, something has to go in the opposite direction at quicker than that speed. But it seems that that's not the way that it works.

You know with regards to gravity, if you were, I'm pretty sure that this is a common thought experiment, if the sun was to disappear like that, how long would it be before the gravity effect hit her? Eight minutes. The same as life. Right, okay, so gravity comes at the speed of light as well. Yes, exactly. That's something Einstein's theory of general relativity same as life. Right, okay, so gravity drops the speed of light as well. Yes, exactly. That's something Einstein's theory of general relativity

explained as well. And it's the speed that say those gravity waves that we were talking about before in terms of these LIGO experiments, the detect gravitational waves, that's the speed they also travel that. So it's very interesting that we didn't know that for sure. It was a prediction of Einstein's general relativity, but when LIGO detected the merger of two neutron stars, which obviously we can see still, because they're not quite heavy enough

yet to trap light, there was both a gravitational wave and a burst of light from it, which was astronomy's worst kept secret at the time when it happened a few years ago because literally every telescope in the world dropped what they took and moved to look at this thing to record it as soon as they'd had the alert that this had happened.

To the point where we have Twitter bots these days as well that's like the Hubble Space Telescope is now looking at such and such a star for this person. And this happened and we were like, that person works on neutron star collisions. And the next day it was like, such and such a person, that person works on neutral and star collisions. And like the next day it was like, such as such a person, that person works on LIGO,

you know, immediately like there was all these constituting and everyone knew what was going on. And obviously, you know, everyone has mates at telescopes and stuff, so eventually sort of word crept around that that's what had happened. So we all knew it was coming to know that, you know, have it confirmed or not whether

gravity traveled at sort of the same speed as light did. I like the idea of a VIP guest list for working out what's going on in the universe. And if you're on the right, if you're in the what right WhatsApp chat, then you get to find out when cool stuff's going to happen before everybody else. Yeah, or if you just happen to be like scheduled to use that telescope that night, then you know, doing your own sort of stuff and then someone comes in and goes, no, sorry, we just need an hour to look at this thing. We're busy this evening. We've got to focus it somewhere else.

So, yeah. You've said earlier on that there is potentially an upper bound that black holes could potentially become full. Does that mean that the event horizon creeps out then? Does the event horizon become bigger as a black hole increases in size? Yeah, so the event horizon or the Schwarzschild radius is related directly to the mass of the black hole. So when we say the size of the black hole, we mean the size across, we mean like the diameter almost of the event horizon. And when we're talking about the mass, we're talking about her heavy is it? And the two are directly related and what basically what the Schwarzschild radius is is an equation to tell you how big is that diameter of the event horizon, given how big your black hole is.

And it's basically just depends on how fast is the speed of light, how strong is gravity, boom, there's your radius for when light can't escape from it anymore. And it's a really simple equation. And I just, I mean, I would encourage anyone to Google Shvartshard radius right now and put your own weight in there. And you can work out what size of a black hole you would be. I've done it many a time and it's quite fun that you're like, I am not point, not, not, not, not, not, like many, many zeros. One meter size black hole, if I could squish myself down into a black hole. Do black holes ever form without a neutron star? Is it possible that sufficient material would be able to come together, or if it did that, would it form a star that would then

live a life that would then collapse in on itself, that would then become a black hole? Just all depends on how big this star is that lives before. So something like the sun won't make a black hole, it will make what's called a white dwarf, which is again the baby sibling to a neutron star. Something heavier than the sun, let's say three times to ten times the mass of the sun will become a neutron star at the end of the life. It will go supernova, throw out all the outer layers so the majority of the mass,

say like seven or eight times the mass of the sun just gets swirled out back into space and that's how we end up with these beautiful nebula that we see, these big round nebula. And at the middle you'll leave behind the core. And if it's three to ten times the mass of the sun that's the star beforehand, it will be a neutron star that core. But if the star's heavier than say ten times the master's sun, up to say a hundred, two hundred times the master's sun, that same process will happen in terms of you have the supernova that throws, essentially you get this rebound of all the outer layers that bounce back off because they're very, very light hydrogen gas with a very heavy core. And the core is what collapses down then into the black hole.

There are some stars that we have seen there one day and gone the next, and have speculated whether those stars have just skipped supernova entirely and directly collapse down into a black hole. Is that my- Direct collapse event? Mm-hmm, exactly, yeah, exactly that. So that's

sort of what you end up with, you end up with this sort of trifecta of the graveyard of stars, basically white dwarf neutron star black hole, and it all depends how big the star was in the first place, essentially. But as we said before, you can add mass to your neutron star. You can keep adding stuff to it and it could become a black hole. And we actually see this happening because the majority of stars are actually not alone like the sun. They're going to be in binary pairs, especially heavier stars. They heavier stars form where there's more gas.

So with more gas, you're going to get more stars and they end up in these not just binary systems tertiary could could reenrower whatever the word is to describe it where you have three four five up to seven or eight stars all orbiting each other in this intricate pattern. So you can imagine if one of them goes supernova and becomes a black hole, which also the biggest stars die first, they burn through their fuel quickest, because they have to burn more fuel to resist the large accrusive gravity because they're so big. And so you have all these other stars with a black hole then. And obviously the black hole can then start to steal material off other stars. Same can happen if you've got a neutron star.

It can pull material off other stars and use it to grow. I'm a kind common black hole. Same is true for a white dwarf. It can pull material off other stars and use it to grow until it becomes a neutron star. And when that happens, when a white dwarf reaches that upper limit as well as its mass, we have another type of supernova, a supernova called a type 1a,

and they always go off at the exact same brightness across the entire universe. Because it's this limit to how big a white dwarf can be before it becomes a neutral stuff. Of course, yes. And you might have heard of these things called standard candles, which are these things that we can use to calculate distances because if they're always the same brightness from how bright they appear, we can look at how far away they are, and then say, okay, this galaxy is at this distance, we now know, and it's got this redshift, this stretching of its light due to the expansion of space, and then we can look at, okay, we'll have fastest

space expanding rewind time. How long it's been expanding for, and you look at how old the age of the universe is. It seems like everything astronomically is moving toward black holes in that case. I guess so yeah, and the fact that if you just keep adding more mass eventually everything will become a black hole. And as we said before, if stars continue to die and you get left behind with all of these things and everything starts to merge and come together over time, then yeah, you would end up with a black hole. It's sort of like the inevitable end to all matter, unless you've got something resisting that crush of gravity down. And the expansion of the universe could be one of those things, right? That's literally moving matter away from, or that likes moving galaxies at least away from other things. So it's obviously

galaxies are held together by their local gravity, but between galaxies, sometimes the pull of gravity is strong enough that it will bring two of them together, like the Milky Way and Andromeda will merge in, say, two billion years. But in other cases, the expansion means that galaxies are majority of the case, most galaxies are getting further apart. What's the best image that we've got of a black hole? It's definitely the event horizon telescope images in terms of we have this one from the galaxy Messier 87 that was the first one was released,

this giant orange donut, and then we had our own super massive black hole in the center of the Milky Way released in May this year. And they are incredible to look at because I mean, I had, I mean, this is what got me into space in the first days, but it's eight years old. I remember I got this book for a birthday or Christmas or something, and it was just a fact file about all the things in space. So it went through all the solar system objects, you know, and they had all the beautiful images

from say the voyage of crafts in the 70s and 80s or even the Hubble Space Telescope. And then you got onto stars and galaxies and black holes. And I remember the black hole page. I was almost annoyed at because on every other page that there's beautiful image from a telescope and on the black hole page it was like artist's impression. And I sort of resigned myself at an early age but I'll be like, yeah, we'll never get an image of a black hole

because they're black and there's nothing to see and whatever and as I got further into my sort of education doing an undergrad degree in astrophysics and my PhD and everything, I realized actually know it could be a possibility if we could take an image of that gas swirling around the black hole and capture that darkness in the middle. And that's essentially what they did and when I saw that image for the first time, I remember getting just goosebumps because I never thought that that could ever, you know, be the case that we could actually see that

for ourselves. And what I think is so powerful about that image, you know, you've got the blackness, eventy space around the outside and you've got this incredibly hot gas plasma that's swirling around the black hole, bright orange, it's colored, you know, so that humans can sort of detect where it's brighter and fainter. And then you've got the blackness in the middle. And you think about the black on the outside is nothingness, and the black on the inside

is everything. Comparing the sort of the two black is insane when you think about how different and yet similar, similar color but so different in nature almost as well of what those two things are. And I mean, I get goosebumps every time I see it when I remember that and really think about it, stop and think about it. James Webb telescope recently went up some incredibly interesting and or inspiring images coming from that. What's next as one of the experimentalist observists that's not just theoretically writing this stuff down? James Webb has been planned for what decades, now three decades, something like that, maybe even more. Yeah, it was originally five years, I think it's now 20 years,

is the sort of promised time, but could be longer if it doesn't need to use as much fuel, essentially. So what is next in terms of telescopes, or we've already mentioned about this, a gravitationally stable triad of mirrors that are going to follow the universe around like a little tale. What else is there? After the James of Space Telescope, there's so many more telescopes coming and so many things to get excited for. One I'm particularly excited for because in my research field, it's really going to have such a huge impact. It's something called the Extremely Large Telescope, the ELT, that is actually its name.

It is extremely large, it's 30 meters across. So James Webb, we think of that being very large, 6.5 meters across, so maybe a two-story house, but with 30 meter mirror to collect the light, as much light as it can and focus it down, it's just incredible to think of how big that would be, you know, sort of mansion sized telescope almost. And that's going to give us better resolution in the Hubble Space Telescope, but from the ground, not from space where you're not looking through atmosphere that just sorts everything. And so that's going to be an incredible thing because not only will that telescope be able to take, say, a single image of, say, a galaxy, what it will do is almost like mosaic

a galaxy up into little segments and observe all of those simultaneously, but not just take an image from each one of those segments, it will split the light through a prism into its rainbow, into its spectrum of light, and make a trace of how much light of every color you're receiving. And that's critically important because elements in the universe give off specific colors like a fingerprint. And so we know how much hydrogen or oxygen or nitrogen there exists in a galaxy, and how that relates to, how many stars are that relates to how many stars are forming or how many stars are dying at that time.

And you can do it in every single little segment of that galaxy, which the amount of detail we're going to have from that, the kind of resolution we're going to have in terms of a Hubble resolution, but from the ground and being able to do this piecing together is something I'm really excited for. And then you've also got massive radio telescopes being built as well. There's something called the square kilometer array being built to one in South Africa and one in Australia. The ELT that just talks about in Chile and they have to come it as it. But these square kilometer array really

is what it says in the tin. It's an array of radio antennae spread across a square kilometer. And you combine them so that they become one telescope that is a square kilometer. So not like 30 meters across, but a square kilometer across. Because as you get to longer and longer wavelengths of light, so the wavelength being sort of the distance between the peaks of light with radio light, for example, which is the light we used to communicate, you know, we send radio signals, we send TV signals using sort of encoded on radio light because the wavelengths are meters, tens of meters long. We can detect that light from space as well and it tells us usually where there's like

magnetic fields and stuff like that in space and also hydrogen gas as well. It also has this resonance in radio light too. So, this fact that, you know, as you get to larger, longer wavelengths of light, you need a larger telescope to detect it. This is why we have to keep going to these square kilometers, but it also means your resolution is incredible as well. The thing, the size of the thing you can actually resolve on the sky, just gets smaller and smaller, the bigger your telescope gets as well. So, I mean, the resolution we're gonna have with a telescope

that is a square kilometer across. It's just gonna be insane. Dr. Becky Smaathas, ladies and gentlemen, if people want to keep up to date with the stuff that you do and everything online, why should they go? So I'm on YouTube, Dr. Becky is the channel name, and I chat about basically what we've been chatting about now, sort of like the questions that you're not able to Google because all you're

going to get back is, you know, just research papers that are written from, you know, by my colleagues for, but you know, my colleagues in the general public just don't have a hope of, you know, going through all of that language and jargon that we use. So it's sort of like, I act as a translator if you will on the channel Which out about what's new in space news and things like that? but also you know Twitter Instagram and From my books as well. Becky. I appreciate you. Thank you Thanks

Oh, yeah, oh, yeah, oh, yeah.