Daniel and Jorge Explain the UniverseDaniel and Jorge talk about the recent picture of the black hole at the heart of the Milky Way
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Hey, Jor, Today is Happy Astronomy Donut Day.
Ooh are they giving away free donuts at every telescope?
Yeah? You know. Today is the day that astronomers around the world get together to gaze in awe at the picture of a donut.
Oh man, I need your physicists like snacks, but to dedicate a whole day to that, it says, taking it to a whole new level.
Max. Donut jokes are pretty sweet.
Yeah, they really make your eyes glaze over.
They're like the frosting on top of your breakfast.
What's so special about this donut?
Strangely enough, one of the weirdest things in the universe looks like one of the most normal, everyday objects through a telescope.
Hmmm, I'm not sure a donut is an everyday object unless you lead a very unhealthy lifestyle.
Well, maybe today's podcast will inspire you to start eating.
What are these like, star flavored donuts?
I don't know what a star would taste like.
Pretty brightly, I'm sure, little spicy.
Probably I'd like a donut covered in sparkles. Please.
Hi.
I am poorhand made cartoonists and the co author of Frequently Asked Questions about the Universe.
Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And it's actually pretty rare that I eat a donut. Oh.
Yeah, I'm rare because you usually do other things with donuts.
Yeah. I usually build donut colliders and push them towards the speed of let just to see what happens.
Oh man, I do want to see what happens. Do they like, morph into a cronut or do they transform into piece of veal or something.
They actually get contracted into pancakes?
Oh wow, doughnut flavorite pancakes. I think you've just blew everyone's mind right.
Now, because that's what pancakes need. They need to be deep fried and even sweeter.
Oh man, it sounds like the next hipster trend. Donut pancakes or a donut pancakes sandwich.
Oh man, put some bacon on top.
Then you're done. Yeah, you're done for life. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we serve up the most delicious breakfast ever, an intoxicating stack of knowledge about the universe. Stuffed with mystery and cluelessness. We chop up the biggest questions in the universe, from what's going on at the center of our galaxy to how did it all form? To how does it all make sense on the very smallest level. We don't shy away from any of these questions, and we talk about them with a healthy dose of silly Dad jokes and a few bites of a donut.
Yeah, because it is a very tasty and delicious universe and we like to roll it up here at the podcast, bright it up, and dip it in coffee in order to give you a big bite of this amazing and incredible and awe inspiring cosmos.
You think physics needs a sweetener, that we need to like add comedy to physics to make it go down. If physics like the medicine we're trying to get people to swallow.
I don't know how bitter are you, dannil.
Oh. I'm mellowing in my old age. I'm no longer very cynical, but I do feel like physics has this reputation of being hard to understand or weird or intimidating or not for everyone. And you know, that's one of the reasons why we do this podcast is to try to make sure everybody out there has access to these ideas and can have fun thinking about them.
Yeah, because technically everyone is physics, right, I mean, we're sort of made out of particles and put together by physics. And also, physics effects are everyday lives. Every day you wake up, you are in a planet floating around in space governed by the laws of the universe.
Assuming that there are laws that we can figure out that humans are capable of deriving these ideas that control the whole universe. It's a pretty big notion. But we do our best to cast our minds out into the universe and try to wrap it all up into our little brains.
And we have been doing our best. Humans have done an incredible job of From our little perch here and this little rock floating in a corner of the Milky Way, we've been able to look out into the universe and period the incredible things happening, and even deep within galaxies.
That's right through history, we've sort of expanded how far out into the universe we've been able to see and our sort of mental map about what's going on out there. Remember that just one hundred years ago, we thought that our galaxy was the only thing in the universe. And now we can peer through all the stars in our galaxy to see beyond it to other galaxies to understand the incredible depth of the cosmos, and we could also look into the heart of our own galaxy to understand what's going on at the center.
Yeah, because while we've been able to look out into the far reaches of the observable universe, there is still a very big mystery right here in the middle of our own neighborhood.
That's right. We sort of live in suburbia in our galaxy. We're like twenty six thousand light years from the center of the action, and we wonder, like, Hey, what's going on down there? Is that part of the neighborhood totally different from our part? Is there something crazy going on? Is it just a bunch of stars? Yeah?
I kind of like living in the suburbs of the galaxy. You know, as you get older, you're like, oh, I liked living in this small town where you can say hi to people in the street and walk your dog if you have a dog.
Well, it's definitely a lot more habitable. If we were closer to the center of the galaxy, there'd be incredibly intense radiation, and so life as we know it would be pretty different.
Yeah, everyone would have a nicer tense, I guess.
And on the far outskirts of the galaxy there aren't as many heavy metals perform interesting chemistry. So right now we're living in sort of the perfect slice of the galaxy for our kind of life at least to evolve.
Yeah, it's a pretty good place to raise a family, I guess, is what we're saying. And the schools are pretty good.
Too, and the donuts are pretty tasty.
Well, speaking of donuts, recently there has been a big news event about a very interesting and very heavy discovery right here in our galaxy.
That's right. We have been wondering for a long time what exactly is going on at the center of our galaxy, But it's very hard to see precisely because between us and the center of the galaxy is a lot of gas and dust and other things obscuring our view. And so while we've been able to get hints about what might be happening at the center, is there a black hole? How big is it? How small is it? Until very recently, we haven't been one hundred percent sure what's there, not until at least we trained a special Earth sized telescope to take a picture of it.
So today on the podcast, we'll be tackling the question what is the center of our galaxy? Or what does a black hole in the center of our galaxy look like?
And what would it taste like if you took a huge bite out of that cosmic donut.
Oh man, it'd probably be very fatting. You know, it's very dense with calories.
It would be a massive, massive undertaking.
You probably wouldn't need to eat for the rest of your life or be able to eat anything for the rest of your life. It'd be the last thing you would eat.
And so you've probably seen by now what this picture looks like, because it came out very recently and there was a lot of science headlines and a lot of news about this. Everybody was very excited. And if you haven't seen it, then essentially it looks like a black image with a glowing orange ring on it, something like a big, fat, glazed donut.
What is the glaze made out of? Daniel particles going at the speed of light close to the speed.
Of light, sparkly, electron frosting.
I have no idea, but yeah, this was pretty big news because I guess it's the first time we get a picture of the black hole at the center of our galaxy, because before we just thought it was there, or we saw evidence that it was there, but it could have been there could have been something else in the middle.
There that's right. We had sort of indirect evidence of the existence of that black hole, and we actually talked in the podcast once about how it might be something else, some weird darky no matter. And recently scientists have developed a technique to take these pictures to train a bunch of telescopes all around the Earth, And they did this a few years ago for Another black Hole M eighty seven and released the first picture ever of a black hole, And now they've done the same for our galaxy.
Yeah, it's kind of funny that with the first picture of a black hole we've ever gotten as a human species was from another galaxy, right, Like, we have a black hole right here in our house, in our neighborhood, but the first one we took a picture of was somebody else's black hole.
Yeah. Well, our black hole is actually harder to see than the one in the neighboring galaxy. It's sort of like, you know, if you're in your own house, it's harder to see what's on your roof because you got to look through the house. But if you look out your window, you can see what's on your neighbor's roof pretty easily. And so the neighboring galaxies. Black hole is actually easier to spot than the one in our own galaxy because of all the stuff between us and the center of the galaxy.
I see. So if your neighbor's kids post for pictures more easily than your kids, that's what you would take a picture of and hang out around your house.
No. No, but if I had just invented the camera, I might test it out on the neighbor's kids first before I take pictures of my own.
In case of camera does something to its subjects.
Oops, I didn't realize I built a death ray in my camera. Sorry guys, Sorry neighbor. But yeah, it was pretty big news. It was on the headlines of the Science news and people were pretty excited about it.
Right. It's like, you know, this is like our black hole. People are calling it our black hole. I think it was a hashtag on Twitter.
Yeah. The scientists are very excited. Some of them have been working on this black hole for decades. One of them said, I've thought about Sagittarius astar for a long time. Twenty two years ago with my first paper on this black hole. So seeing the picture was like online chatting for years and then finally meeting in person and realizing, wow, you're real.
Yeah, and we'll find out if he or she was disappointed or not exactly.
But it was a big event in science at least, and so I was wondering, you know, had people heard about this, had this penetrated into the life of the everyday person.
Yeah, So, as usual, Daniel went out there into the world to ask people walking on the street if they had seen the new pictures of our black hole and if they knew what it might look like. But the news just came out just yesterday, right, Daniel, So did you just run out of your office right away to record people?
I did. I was curious whether UCI undergrads have their finger on the pulse of the science news or whether they had no idea what I'm talking about.
To think about it for a second, where were you when they polished the first pictures of our milky ways black hole. Here's what be glad to say.
Have you seen the latest picture of the black hole at the center of our galaxy?
No?
I have not. What do you imagine that it might look like very empty in the center, but surrounded by what may look white and black around the surface.
Have you seen the latest picture of the black hole at the center of our galaxy.
No, what do you imagine a black hole might look like if you could take a picture.
Of it, Like a big amorphous mass with like stars and planets in it.
Yeah, And what do you think we might learn from taking a picture of Why do scientist want to take a picture of a black hole like for measuring?
I didn't think that black hole will look like that.
Oh what did you think it would look like?
Just a hole.
Nothing around it?
So what do you think we've learned from this picture?
Something that no one who would have thought off it would just shine some light that it would help other people to learn something on top of what we have learned from this new picture, I.
Guess what does a black hole look like?
I feel like because space is really dark and just be mostly black.
But since they're.
Probably using like rays or something to try to like figure it out, maybe like in the photo there's like some like orange and like black in the middle or something.
And what do you think we learned from taking such a picture? Why do scientists do it?
I think it's good to have in your records and study that, like how far our reach can go? And like have tangible evidence and use that to kind of what we already had in mind versus what it actually looks like.
What do you think a black hole might look like? In your imagination if you took a picture of what would you see?
Black?
Black and stars?
I feel like, yeah, very bright flowing because its supposed to be like an explosion, right.
It's like stars, So I feel like very sparkly.
Kind of yeah, yeah, colorful.
I would think it'd be the opposite of what it's called, because scientists are not good at any things.
Yeah, I feel like it would be dark because I feel like, isn't black the most dominant color?
And black holes kind of absorb everything.
I feel like it'd be dark in the center and then sparking on the outside, like with everything that's consuming.
Yeah, what do you think a black hole would look like if you could take a picture of it?
A black hole to me like in a galaxy in that in space. It's like a hole in space.
It's like like if you're looking at like water draining, That's what I would imagine it looks like, but like a black form of mass, I guess, is what I would imagine it would look like. I don't think I've actually looked at a photo of a black hole.
What do you think scientists learn from taking this picture? Like? Why do they do it?
I mean, I think it's also an issue of if a major mass black hole forms, it sucking us in and then potentially causing catastrophe in that sense and kind of preventing I guess world domination.
Of black holeness watch out for.
Yeah, I personally would not want to be sucked into a black hole.
I feel like you got a lot of wiseky answers here, like the person who said, it just looks like a hole, a whole lot of nothing.
Well, almost nobody had actually seen this picture already. They're not like desperately tuned to science news the way I guess physics professors are. But I asked them to speculate what they thought a black hole might look like, and they came up with some pretty creative answers.
Yeah, creative and accurate too. I mean, it does look just like a hole. A black hole does look like a hole.
Yeah. And the girl who said, you know, maybe a hole with a bunch of sparkling stuff around it. I showed her the picture later and she was like, wow, I should switch to being a physics major.
Hey, yeah, or psychic reading or something.
I was sending her the answers with my mind.
Yeah, and somebody else said, it just looks black, black, but mostly black. What would the other non black?
There's so many shades of black, man, you can't just order black paints if you go into the paint store. There's like black hole black, there's matte black, there's zen black.
You know, I see. Yeah, you got to choose your paint colors carefully. They might absorb all of your house or something if you picked the wrong one. But yes, some pretty big news. And so I guess a lot of people are wondering, what is this discovery about? How did we actually take a picture of this black hole? And what does it mean about what we understand about our galaxy.
It's actually kind of a big moment in understanding something about black holes and in understanding the nature of our own galaxy. So even though this just looks like a big donut and it sort of looks like the last doughnut we saw, we really did learn some fascinating facts about our own neighborhood.
Another donut is never just another donut, Daniel, You know, you're hooked.
Once you have one donut, you're like always thinking about that next donut. And these scientists are no different. They're just people.
You should glaze it with some addictive drug with knowledge. All right, Well, a step people through this discovery, and I guess we'll start with the basics. What is a black hole and what are some of the things we still don't know about black holes?
Right? So, black holes are these weird locations in space where there is so much stuff crammed into a small area that the gravity is so intense. The curvature of space is so intense that there's a trapping region, an event horizon, a sphere within which if you fall into it, you cannot escape. No information can ever leave the event horizon because space has bent so strongly within that event horizon that it becomes one directional. Every path leads towards the center of the black hole. No matter what direction you shoot a photon, it will always end up at the singularity. So black holes are these strange divots in space, originally predicted by Einstein's theory of general relativity and then actually seen out there in the universe. Black Holes are not theoretical. We are certain that they are out there, and some of them form when stars collapse at the end of their life cycle and they can no longer resist the pressure of gravity, squeezing them down into a dense spot. And there are also black holes at the centers of many galaxies.
Yeah, one thing that's interesting about black holes is that they come in many sizes. Right, Like, you're going to have a tiny little black hole the size of your pinky finger, and you can have one the size of like ten bazillion suns, right.
That's right. The key thing is the density. You can take almost any amount of mass and make it into a black hole if you squeeze it down to a small enough radius, because then space gets curved because remember that gravity falls rapidly with distance. So if you have like a large object like the Earth, you're pretty far from the center of the Earth, essentially where the gravitational power comes from. But if you squeeze the Earth down to the size of a peanut, then you're getting much closer to all that mass, and so the gravity is much much stronger, and a peanut sized Earth mass could actually form a black hole. Black Holes come in a huge variety of sizes. Some of the millions or billions of times the mass of our sun.
Yeah, it's pretty amazing. And most of the big ones, I guess, are in the middle of galaxies. And I guess the question, Daniel is how do we know this, Like, how do we know galaxies have super massive black holes in the middle of them?
Yeah, we think that galaxies form with black holes at the hearts of them. And until we had that picture of the black hole in eighty seven, we were in one hundred percent sure that they really were black holes. We had sort of indirect evidence for the black hole, because again, you can never see a black hole directly because it doesn't give off light, it doesn't reflect light, it absorbs all light. So what we'd seen before we saw these pictures were just like stars orbiting around some location in space that seemed to have very strong gravity. And we can do calculations to think, like, well, what could be that small and have that much gravity, And the only thing that fit the bill was a black hole.
It's sort of like we've seen the traffic around the black hole, but we had never seen, at least until a few years ago, at an actual picture of a black hole.
That's right, and a purist might say that we haven't even still proven that black holes exist, because in the end, what we're doing is always taking pictures of the traffic around the black hole. Until recently, we were doing things like looking at stars that were whizzing near the black hole, but not getting even that close. What these pictures allow us to do is to look even closer. Basically, they're taking pictures of the stuff immediately around the black hole rather than stars in sort of a more distant orbit. So it gives us a better way to understand how small it has to be, and that makes it more likely to be a black hole. But still we're never one hundred percent sure, because all of these things are always indirect.
I see, well, I guess Philosophically, it's impossible to take a picture of a black hole, right Like when you take a picture of something, you're taking you're capturing the photons that bounce off of something like your kids, or you're taking you're capturing the photons that come off of a star. But a black hole like literally doesn't by definition, doesn't emit anything. So it's it's actually technically impossible to take a picture of a black hole.
It's technically impossible to see a photon that has been within the event horizon. You could see photons do things like orbit a black hole right, move in a circle around a black hole, and from that you could argue that there has to be something there with incredible mass and a small radius. And then you know there's one more leave to say only black holes could do that, And that's a leap, because you know that's our theory of physics. Maybe somebody else one day will come up with another idea for what could be there. We talked once in the podcast about the idea of dark stars. Maybe black holes are not actually black holes, they're just very slowly collapsing stars that they're going to bounce back eventually one day. So in principle, you're right. You can never take a direct picture of this object. You always have to use some physics ideas, some model to interpret the indirect information you gather from what's happening in the very close vicinity. The name of the game is to get as close as you can to narrow down the spectrum of options.
Right, right, And do you volunteer to get close to a black hole to take a picture.
I volunteer to receive ten billion dollars from the government to build a telescope that lets me take pictures of photons that went very close to the black hole. So yes, thank you very much.
Several levels removed there. Just add the donuts too, Like, get why did you get paid in dot?
Why don't we put donuts in orbit around the black hole? That would be pretty awesome, you know, just like shoot a series of donuts.
That sounds like an enormous waste of taxpayers dollars.
Wouldn't you like to see a black hole tear part of donut? I mean, come on, you would watch that video. If I had a video right now of a black hole spaghettifying a donut, you would watch it.
It sounds like a tragedy, Daniel. There are so many other things you could throw at a black hole to see it get spaghettified. Why a donut?
Well, that gives me another idea for a terrible dish, pasta made out of donuts. Has anybody ever done that?
Donut spaghetti donut spaghetti?
Yeah?
Interesting, it's a donut made out of spaghetti or spaghetti made out of donuts.
Spaghetti made out of donuts? Like, what would happen if you threw a donut near a black hole, it would get spaghettified. So we're just doing that for you and serving it up and charging you fifty bucks.
Oh man, we'll add that to the many of our physics. Theed restaurant that we talked about last.
Time, somebody's working on that, right, We have somebody on it.
Right, We have people. Our manager is looking into the business model for.
That, so I'm sure they're getting investors ready. But we studyed black holes not just by looking at the stars in orbit around them, but also by looking at their emissions. The stuff that's closer to the black hole than actual stars is this accretion disc and it's filled with gas that's really really hot and giving off all sorts of particles and X rays. Some of these guys emit very very bright beams of light sort of up and down along their spin axis, and these are called quasars, and quasars are actually the reason that we believed black holes exist in the first place. We saw these very bright beams of light and we couldn't understand what else could be making them, these very distant, very bright beams from the early universe until people understood, oh, maybe a black holes accretion disk was powering this radiation.
Interesting, that's the only thing that could explain a quasar, Like, it couldn't be a dark star or some other interesting, maybe new physics object in the middle of there. It had to be black holes.
The idea of dark stars hadn't been born yet when people were discovering black holes in the sixties or seventies, so it's sort of like anything in that category had to be something that small and that dense. People didn't realize that that was actually something out there in the universe. They thought black holes were like a theoretical concept, not something that would ever actually form, And when they saw these quasars, they realized something needed to be really incredibly gravitationally powerful in order to create these quasars. So, yeah, you're right, it could be that dark stars are at the heart of every galaxy or something else weirder, some quantum gravity theory that's even stranger. But it had to be something very small and very compact and very dense.
I feel like she work for Marble there. That sounded like a very exciting movie. So there is a black hole in the middle of our galaxy, and I guess thankfully it's not a quasar, right, because if it was a quasar, we might be fried.
Right, that's right. We're glad actually that that black hole is not a quasar. These quasars don't emit in every direction. They tend to admit sort of up and down along their spin axis. So it depends on where that quasar is pointed, where the black hole is pointed. But it would be dangerous if it was a quasar. It could be like sweeping out through the universe or sweeping out through the Milky Way. But we didn't know a lot about this black hole already. There was a Nobel Prize given recently to a couple of folks for studying the motion of stars in the vicinity of the black hole, which was really very strong evidence for the black hole.
Hmmm. Interesting. So there is a black hole in the middle of our galaxy and we know some things about it, but we don't know everything about it. And we also don't know a lot about black holes in the middle of galaxies how they get so big. And so let's get into the discovery that's made the news recently, and let's talk about the big black hole, don'ut. But first let's take a quick break.
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All right, Daniel, we are putting together the many of our physics themed restaurant, and there's I guess for dessert there are going to be black hole donuts or black donut holes.
I think everything should be made out of donuts. You want a cup of coffee, We took some donuts and we somehow turned it into coffee. We serve donut juice, donut pancakes, doughnut spaghetti.
M donut bananas. We might need a biologist for that one.
We need another billion years of evolution.
Yeah, but it's kind of interesting that we took this picture of a black hole in the middle of our galaxy, and everyone started calling it the donut. It was like really popular to use the word donut.
That's right. And Krispy Kreame, the company, even got into the game, and they are today giving away free donuts. You go into a Krispy Creame today, you can get one free glazed donut in honor of this discovery.
Wow, that's amazing. And unfortunately I live far from a Krispy Kreme. But the Daniel, have you gone in your Crispy Kreme donut yet?
No? I haven't known.
Don't you want to celebrate.
I'm going to celebrate as soon as we finish this podcast, So let's get on to it, all right.
Well, so there's been a picture taking of the black hole in the middle of our galaxy, and it's interesting because it sort of confirms that it's there, right like we sort of before thought it was there. Knew a lot about what was going on there, but we weren't one hundred percent sure there was a black hole.
That's right, And let's be specific about what we knew and what we didn't know, and then what we've learned today, because I think it's really quite interesting. What we knew already was the mass of the black hole. We knew that it was four million times the mass of the Sun, and we can measure that because we can look at its gravitational impact on stars nearby. We can calculate the strength of gravity, and we know the distance, and we can see stars whizzing around this black hole. So it's not hard to figure out how massive it has to be to explain all the stuff moving around it. The question that remains is how big is it? Or to figure out how big it is is harder because you know, a big object and a small object with the same mass have the same gravitational effect, So you can't tell the size of this thing just by looking at how the stars move. You have to look and see what comes close to the black hole.
Well, I guess maybe help me understand here. I feel like you're saying that we could see the stars going around the black hole, but somehow we couldn't see the black hole itself. Like, I know, it's in the middle of the galaxy and there's a lot going on there and it's kind of hard to see in there. But we could still see sort of the stars that are very close to the black hole, right, like those you can see right with regular telescopes.
That's right. So we're looking at the center of the galaxy with different kinds of eyeballs because the center of the galaxy is clouded with gas and with dust, so in order to see stuff you have to use special kinds of telescopes. We can see the stars, for example, they shine through the gas the dust, especially in the infrared, So we can use the infrared to see these stars. So we can track the path of these stars and see as they move around, and that tells us sort of where the black hole should be, and it tells us how massive it is.
But I see the stars sort of shine through all that stuff that's in the middle of the galaxy. But I guess the black hole doesn't shine through, right, because it's a black hole.
And it's also super duper duper small, right, So the kind of thing that we're looking for is really really tiny. It's like if you were trying to take a picture of a donut that was on the surface of the moon. So you need a very very powerful camera in order to see the stuff that's right around the black hole.
Wait, what like the equivalent size of the black hole in the middle of our galaxy is the same as trying to see a donut on the Moon.
Yeah, if you put a donut on the surface of the Moon and try to take a picture of it. Another analogy is that if you were sitting in Munich in Germany and you were trying to take a picture of bubbles in a glass of beer in New York City. Like, it's a big object, but it's incredibly far away. The center of the galaxy is twenty six thousand light years away, and this thing doesn't emit a lot of light, right, it's black. So we're trying to take a picture of stuff around this and also see the hole in the middle of it. So it's a very very challenging problem.
Right, it's super far away. And also, I mean it's not that big cosmically speaking, right, I mean you might think that a black hole as being this huge thing, but and it is four million times the mass of our Sun. But in terms of size, like four million times the mass of our Sun for a black hole is not like one of those super giant ones you see out there in other galaxies.
That's right. The other black hole that we took a picture of previously M eighty seven was more than a thousand times as massive, so it's like six and a half billion times the mass of the Sun, which made it much much bigger. So even though the previous black hole that we saw M eighty seven was much bigger and much more massive, it was also much further away. So weirdly, these two black holes are about the same size in the sky, like our black hole is smaller and closer when we took a picture of before it's much bigger, but further so, they're about the same size in the sky, like the Sun and the moon are the same size and the sky, even though one is obviously much bigger than the other.
Right, right, And what if you put a donut on the surface of the Sun.
Then you get a toasted donut.
So I think what you're saying is that our black hole in the middle of our galaxy is basically like a baby black hole, right, It's like a thousand times smaller than some of the big boys that you see out there, exactly.
And so to put it in like more familiar units, the width of this black hole, the radius of it was predicted to be about zero point oneau like ten percent of the distance between the Earth and the Sun. So if you like put it in our solar system, it would fit within Mercury's orbit. Right, It's not that big compared to like other astronomical objects. There are stars out there that are much bigger than this black hole.
Oh wow, So it would fit within our solar system, but it would probably make our solar system collapse, right because it is four million times the mass of our Sun exactly.
I'm not suggesting any try this. I'm just trying to give you a sense of scale. So we knew how massive it was, and that tells us how big it should be. The problem is, how do you actually measure its radius? How do you tell how big this thing is? All we had previously were stars that are whizzing around it, but they weren't coming that close to the black hole. They only came to within like twelve or fifteen AU of this black hole. So we knew there was a big, massive thing there. We knew that its radius had to be less than about twelve Au, but that didn't mean that it was a black hole with the radius point oneau. So we needed to do was like verify that it really was that compact that it wasn't like a larger, fluffier object.
I see, because I guess there's sort of a one to one relationship between the mass of a black hole and its size, right, Like black holes don't vary in density. I guess, like you can't have a fluffy black hole and a really compact black hole. It's like a black hole is a black.
Hole mostly, Like if we're talking about black holes that don't spin, then a certain mass black hole tells you exactly the radius. You can look it up. It's called the short styles radius. It's a very simple calculation. If black holes are spinning, it's a little bit different because then they're radius to a little bit on their spin, but not by a factor of like one hundred or ten. You know, we're talking about like a factor of twenty to fifty percent. If it's spinning, it can be a little larger or smaller. So mostly a black hole's radius is determined by its mass, as you said.
But then how do we get the prediction for our black hole because did we know if it was spinning or not.
We didn't know if it was spinning, So the prediction there is just for like a short styled black hole, but still we only had like data that suggested that it was smaller than like twelve AU and the prediction for a non spinning or a spinning black hole, we're all much much smaller. They were like five percent or ten percent of an AU, So we were like an order of magnitude away from really knowing even that this was a black hole until we got data that came much much closer to the center of the black hole, right.
I think we talked about this in another podcast, like we a physicists saw a cloud of gas get near the black hole and that sort of give us an estimate of how big it was.
Yeah, there was this gas cloud G two, which people saw was like on a path to go pretty clear close to the black hole and give us a sense for what its strength was. And it was pretty weird because people expected the gas cloud to be torn up by the tidal forces in the gravity of the black hole, and they thought that would really give them a clue as to how powerful it is and the radius of it. But it sort of wasn't torn up the way they expected, which made people wonder like maybe it's actually a big, fluffy object. And then gas clouds sort of passed through this big fluffy object instead of like a dense object, and just at the heart of it, other people thought, oh, maybe it's not just a gas cloud. Maybe there's like some stars inside of it holding it together. So that was a bit of a mystery, and it led people to suggest instead of there being a black hole there, maybe there was a big fluffy cloud of weird dark matter objects called dark eenos. And we do indeed have a whole podcast episode.
Exploring that one I see, right, we need the stars around that area were going around something heavy, but we didn't know if it was a black hole or something just really dense, right, because it's kind of impossible to tell, or it was impossible to.
Tell exactly, And the most conclusive way to know that it really is a black hole is to look at the accretion disk, the stuff that's the closest possible to the black hole, because that will reveal the radius of the event horizon. You can't see the event horizon, but you can see the stuff just outside the event horizon. That tells you where the event horizon is, and if that confirms with your calculation of where it should be, then that's pretty strong evidence that it really is a black hole and not something else. I see.
Well, that's assuming it has an accretion in this, right. Not all black holes haven't accretioning this.
That's right. It's assuming that it has one and that you can see it. Right. And so if it's a black hole that's just all by itself, then you have no hope of measuring its event horizon directly unless you're shooting donuts at it or something. But most black holes, you know, because they are actively sucking stuff in, will have some kind of accretion disc But you're right, until we took this picture, we didn't know what was there exactly around this tiny little dot, superduper far away.
I guess if it doesn't have an accretion disk, you could still see like how it blocks the light that's coming from behind. It's right, If you look at a picture of the sky, if you're I guess you need to be closed. But if you're up closed and you see that there's a spot in the sky that you're not getting you know, images of pinpoint stars behind it, then that's also sort of a picture of a black hole. Right.
You'd have to know a lot about the light field behind the black hole to know what you're missing, so you're not confusing it, which is like, oh, there's a gap in the stars or there's something else blocking you that's even further away. Right, it looks to be that size. So that's what the most direct evidence is in accretion disc immediately around the black.
Hole, right, And that is what the picture that was released yesterday was. It was a picture of basically like a ring or a bright donut.
That's a bright ring. So you're seeing the accretion disc. You're seeing light emitted from the gas around the black hole, and then very excitingly, you see a hole at the center of it. You see something black Like if it had been just a circle, they would say, hm, that's weird. We're seeing light from where there should be a black hole. So that would have been disappointing or it would have confused us. But we in fact see a ring and we see a hole the center of it. That hole is exactly the size you would expect it to be if there is indeed a black hole with mass of four million times the mass of our sun.
Yeah, so you can look up pictures of this space donut. If you look up I guess milky way black hole and discovery. You probably find pictures of it now, Daniel. I'm not a conspiracy theorist, and I totally trust you physicists, but it is a little suspicious. I think that the two pictures of black holes we've gotten are like these perfect little donuts, Like, what are the chances that these two black holes that we look at You're looking at the doughnut right, like from the top of the doughnut, right, because the doughnut could have been on its side, and then we'd be like, oh, what is that.
Yeah, it's not a coincidence that these two things look similar. These are the two best target black holes for this telescope, Like the Milky Way black hole is the closest big black hole to us, and M eighty seven is like one of the biggest nearby black holes. And coincidentally, they appear to be about the same size in our sky. So they're like number one and number two targets of this telescope. And we didn't know until we looked at them what their angles were, like, are these things aligned with a galaxy? Are they out of alignment with a galaxy? We didn't know until we looked at them, and it's not even that easy to tell how the accretion disc is aligned because there's a lot of distortion around the black hole. You know, for example, like you can see the part of the accretion disc that's behind the black hole because light from it goes up and it gets bent around the black hole. In two hour telescopes, so you're almost always going to see the whole donut no matter what the orientation of the black hole is.
Right, But if the doughnut is on its side, like perfectly on its side from our view, it wouldn't look like such a perfect donut. Of the picture that we're seeing.
The day that we have is really pretty fuzzy, and so it's not easy to measure the angle of that doughnut. And surprisingly a black hole that you look at sort of side on and a black hole that you look at sort of top down. Remember that a black hole is a sphere, of course, so every direction is the same. A black holes are also spinning, so this accretion disk around them has sort of a direction. Right, it's like flat in two dimensions. It's really like, you know, it's sort of the way the galaxy is flat, or the way the Solar system is flat. This s accretion disc is like a tire around the black hole, right, or like a record, right, a flat object around it. If you look at it edge on, if you look at it top down, it doesn't actually look that different because our picture is still pretty fuzzy, right. We can't really resolve those kinds of differences. They try to do it, and they think they have an idea for what the angle of the black hole is, but it's not as easy as you might imagine. It's not just like if you look at it edge on, it looks like a line. If you look at it top down, it looks like a circle, because there's a lot of distortion from the black hole itself. Even if you look at it edge on, you still see the back of the accretion disk, the part that's blocked from you by the black hole.
I see. I think you're saying that the picture is still not high enough resolution, or it's still fuzzy enough that we actually can't tell if we're looking at the door from the top or the side.
We can't tell one hundred percent. But they do have an idea. The models that they're using to describe as black hole are best described by one where the black hole is actually sort of pointing right at us, Like we're looking at this thing weirdly, almost top down. The data we're getting is most consistent with us looking straight down on the top of the black hole, like the accretion disk is sort of flat with respect to us.
Which is a huge coincidence, right, like you know, right, because it could have been pointing anywhere, but it somehow it seems to be pointing right at us in our spot in the Milky Way.
It is a really big coincidence. You might have expected the black hole to be aligned with the galaxy, right, that its spin would be arranged the same way as the galaxy is spinning. But I remember, the black hole is a tiny little part of the galaxy. It's not like a very big fraction of the galaxy's mass. You wouldn't expect it necessarily to be spinning the same way the galaxy does, the way the Sun spins, the way the Solar system does. Right, the Sun is a huge fraction of the Solar System's mass. It's most of the Solar system, So the fact that the Solar System spins with the Sun, it's not a surprise. The black hole is a tiny dot at the heart of the galaxy, so it can basically spin in any direction. And you're right, it's a big coincidence that happens to be spinning in a way that we look at it sort of top down, and so we're very lucky actually that there is no quoazar there, because they would be shooting right at us.
It's like staring down the barrel of a gun. So I guess what exactly did we see in this picture them? Did it confirm the size that we thought it was going to be or is it the black hole there bigger or smaller?
So it's exactly the size that we expect it to be. Like, we don't have great resolution, but we can measure the event horizon from looking the black hole shadow, and it's to within ten percent of what we expected. It's like, really bang on. So it's in these series of you know, big astronomical announcements that I'll say, yeah, no surprises. Einstein was right again.
That Einstein so annoying, always right.
You know. We love that we have this theory of general relativity that it describes space and space time and black holes and all sorts of stuff. We're also waiting for it to break down. We're desperate to find a crack in it. Not because we're rooting against Einstein, we love the guy, but because we want to learn something. We only learn something when the theory fails, when it disagrees with the universe and gives us a clue about how to change the theory. So it's satisfying that it works, but it's also frustrating because it was an opportunity to learn something new about the universe, to get a clue about the direction of quantum gravity.
Come on, admit a Daniel, you're rooting against Einstein.
Yes, yes, yes, I'm rooting against science. I mean, like, look, we know Einstein was wrong. I mean I get crack upon emails every day to say Einstein was wrong, and I roll my eyes. But the truth is that we do know that Einstein has to be wrong, right. There's no way that general relatively is an accurate description of the universe. It's inconsistent with quantum mechanics. It predicts absurd things like singularities, points of infinite density. We know it breaks down, we just have never seen it happen yet.
Well, I don't think Einstein minds. You know, he's not really around anymore.
I see you're appointed yourself speaker for the Einstein Estate.
All right, well, it is an amazing discovery and an incredible feat of science and engineering to take the picture of a tiny black hole in the middle of a busy and cloudy galaxy. And so let's get into how scientists were able to do this and what it could all means for understanding of galaxies and our origins. But first, let's take another quick break.
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Network all right, we are talking about to take pictures of donuts, right, because I guess pausinists are really just instagrammers.
That's right. And before you eat anything you have to take a picture of it.
I guess yeah, because you're going to eat it and it's going to turn into something gross in a second.
Right, better take a picture of it before you eat it. You're saying, yeah, i'd agree with that.
Yeah, not after you digest it. Definitely. Nobody wants to see those pictures.
Here's my mouth full of chewed up donut.
That's a black hole. You don't want to take a picture of it.
For sure. That's the way to lose followers on social media.
Or gain strange ones.
I guess that's true. Yeah, no matter what your weirdness is, as somebody out there into it.
Yeah, So we took a picture of the black hole in the middle of our galaxy. It was big news and it was a huge endeavor. I mean, you need a telescope basically as big as you can make it here on Earth. It's like the size of the Earth exactly.
They use this event Horizon telescope, which is actually a work of telescopes around the Earth. So it's not like one big telescope the size of the Earth. But if you use a bunch of telescopes simultaneously, you can get almost the same power as if you had a telescope the size of the distance between your telescopes. It's called interferometry. It's really cool technique.
Yeah, because I think maybe something that people don't realize is that, you know, these telecopes don't sort of work the same way as an optical telescope works. I mean, sort of in principle it is the same thing, but they actually use a lot of sort of math and a lot of kind of frequency analysis to sort of resolve the picture.
Right, So these things are not optical telescopes. You're right, there are radio telescopes. So if you actually go to look at one, they're just a bunch of antenna, right. There's not like lenses and curved dishes that kind of stuff. They're just a bunch of antennas. Right. They're collecting radio waves from the center of the galaxy. And the way you put them together to make a really big telescope is that you point them all towards the same location. You synchronize them all with really really precise like atomic clocks. And then when a message arrives from somewhere really really far away, it like washes over the surface of the Earth and you sample it at different places around the Earth and then, as you say, do a bunch of math to reconstruct what must have been sending you this picture.
Right, because you're sort of looking at for the nuances in the signals between like the telescope and Australia and the one in America, and so those subtle differences you have to like use some incredible kind of mass in frequency analysis to resolve those differences. And then somehow those differences give you the picture of the black hole.
Yeah, like you say, somehow like it's magic or something.
Yeah, YadA, YadA, YadA. Twenty years of a PC students of three hundred PG students live and you get a picture.
But it's something that we can actually understand a little bit. It just comes down to interference. Like if you're getting life from two different spots in the sky, one to the left and one to the right, and when they get to your antenna, they're either going to interfere in a way that adds up to each other, like they make each other stronger, or they're going to interfere in a way that destructs each other, that suppresses each other, like they cancel out, because these in the end are just way. So either they push in the same direction to enhance each other, or they push in opposite directions to cancel out. Now, if I'm on one spot of the Earth and I'm looking at these two points in the sky, I'll see a different kind of interference than you will if you're on the other side of the Earth, because the interference depends on how long it took the waves to get to you. So if you have like a different relative distance to those two points in the sky than I do, you'll see a different interference pattern. And if we compare what we are seeing, that will give us a clue about how far apart these two things are and what their relative brightness is. Remember that you only get interference if you are seeing light from more than just a point source. You need some sort of extended source so that you can see different interference when you're on different sides of the Earth, different parts of this extended telescope. And if you just looked at a point, for example, then you wouldn't get interference because all the light would have the same number of wavelengths traversed on its way to you. That's why interferometry lets you understand the shape of a distant object. If it's extended, you can resolve a picture of it by looking at it from different locations to get different interference. But if it has a shape, if it has a size, then we're going to see different things from the left side of it and the right side of it. That's going to give us different interference patterns on the surface. Then, as you say, we can do a bunch of math to figure out what that means. So that's why you want telescopes that are really far apart, because they get like a different interference pattern if they're far apart. And that's the key to reconstructing the shape of this thing that you're looking at.
Right, And I guess we use the whole earth to keep them as far apart as possible. Right, Like, how many telescopes or how many antennas were involved in this event? Horizon telescope They are all over the Earth.
There's three hundred scientists from thirteen institutions, and there's telescopes like in North America and in South America, there's one in the Mediterranean, there's one even in the South Pole. So if you go online you can see what this network of telescopes look like. And for my count's at least six different spots on the Earth that they're collecting data from.
Well, it's pretty cool. It's pretty cool that you know, scientists can work, you know, across countries and cultures like that. Do they synchronize using it like a zoom call because that might be a nightmare.
I know, And they were like muted the first time probably so it had all got messed up. I mean. The amazing thing is that they recorded all of this data five years ago in April of twenty seventeen, over just five nights of observing and they've been crunching the data ever since. Wait what, Yeah, so, like that's how long it takes to analyze the data and make the picture.
That's incredible, just five nights five years ago, and that's the Event Horizon telescope. Like, wouldn't they just keep recording this whole time? Or is it that hard to kind of even get five nights coordinated?
Yeah, And it's hard to get any time on these telescopes, not to mention coordinating time across all of these telescopes, which are run by totally different agencies in different countries. It's amazing they were able to do it at all because remember that you need these telescopes to be pointing at this thing at the same time. The interferometry only works if you have data from the same moments, so you take the picture of the object at the same time.
Whoa Like, even over five nights, it was moving. It was changing.
Yeah, because remember that this black hole is dynamic. It's active, so a picture of it at one moment won't be the same as a picture of it at another moment. But that's also one of the things that made this black hole harder to take a picture of than the last one. Because the black hole is smaller, the orbit time around it is shorter, like it only takes a photon thirty seconds to orbit this smaller black hole, So the whole black hole is like more active. It's frothing and bubbling and burping. So it's like trying to take a picture of your kids when they're running around after eating too many donuts. You're more likely to get a fuzzy picture than a crisp image. That you'd get if your kid was standing still.
Yeah, or your neighbor's kids also.
Unless you also fed your neighbor's kids donuts.
But they're probably more well behaved. Well, that's one of the things we learned about this black hole at the center of our guy see, not just kind of its size, which sort of confirmed everything that we thought it was going to be, but also it's one of the things for Daring is that it is so dynamic. Right, It's not like a beautiful, serene scene. It's like this crazy chaos going on around the black hole.
Yeah, although that was a little bit surprising as well. The black hole actually isn't eating as much as you might expect compared to its mass. It only eats a little bit. Like if the black hole were the mass of a person, like one hundred kilos, it would be only eating the equivalent of one grain of rice every million years.
Wait what Yeah.
This black hole eats like forty solar masses every million years, but its mass is four million solar masses.
Oh, I see, you're saying like its intake is about, I guess millions of times smaller than its actual mass, Like it's an elephant eating a couple of grains of rice every few million years.
That's right, it's not really gobbling that much mass compared to its size.
So wait, are you saying that this black hole is sort of like it's done growing, kind of like it's already ate everything it can eat around it, and so now it's out of food kind of.
It's just because of where it is, there doesn't happen to be a lot of gas around for it to eat. In the future, it might grow more if something comes close. And then when the Milky Way and Andromeda galaxies collide in the future, the two black holes that their centers will form an even bigger black hole.
Interesting, and so this black hole has a name. It's called Sagittarius a star, but it's not a star. It's just it's literally like an asterisk.
That's right. They put a star in the name because it was an exciting discovery.
Wait what for real?
Yeah? Like literally, they use a star to denote excited states of atoms and stuff. And so if they were excited about this, so they give it a star.
Don't they know they can use Miley faces or emojis now, literally, it's basically like they were trying to put a little emoji there.
Yeah, it's like old school text emojis.
Oh for real. Oh but why were they so surprised when they name this.
I'd say they were more excited than surprised.
I guess, well, is there a Sagittarius? I guess, like, why is it called Sagittarius A star?
Well, it's called Sagittarius because it was found near the constellation of Sagittarius. And then back in the fifties, they were scanning the sky for radio sources and found this one near that constellation. It was the first big, bright radio source they found in that part of the sky. So they called it Sagittarius A. And then when they imagine there might be a black hole there, they called that Sagittarius a star.
So it really could have just also been Sagittarius AOMG.
Exactly, that's precisely what the star means.
So they thought it was maybe a star, or they thought it was just like a radio source. But then later I guess we found out it's actually the black hole.
Yeah, discovery of this radio source was one of the things that give us a clue that black holes might be real. They saw this source in the radio but then nothing in the visual So they had to try to understand what kind of thing had so much energy that it could be that bright in the radio but dark in the optical.
All right, well, what are some of the I guess, big picture of things we were learning from picture And what does it mean about our understanding of black holes in general?
Well, it means that we are one step closer to saying for sure that there is a black hole here at the heart of our galaxy. We can now rule out things like, no, there's a much larger object with the same mass as we thought the black hole had. We can rule that out. We know that it's something around the same size as we expect a black hole to be. That's a pretty clear statement. It really rules out some of the other crazier ideas. We also can start to study in more detail, like the complicated astrophysics of what's going on around the black hole. You know, one thing is like the general relativity of the black hole itself. The other is understanding the crazy swirling mass that's near the black hole, that's generating all this crazy radiation, the X rays and the quasars, you know, just understanding how that works. The magnetic feels around there. That's something else that we can now start to dig into.
Oh, I see, because now we have a picture, we can actually sort of measure and see how it's changing. I guess, right, because and then once you know how it's changing, you understand the physics behind it a little bit more, because before it was all sort of theoretical and based on simulations. But now we have like actual data of what's going on around a potential black hole.
Yeah, there are these two competing models for what's going on in the accretion disk, how it forms, how particles swirl around it, how sometimes they fall in and sometimes they get ejected up along the axis of the black hole. These two models are called mad mad and samee sane. So there's two competing parts of the astrophysics community, the mad people and the sane people.
Wait, what those are The acronyms m AD, MAD and sane are the competing theories about black holes.
That's right, you're either mad or you're saying in astrophysics, Yeah, wow, did they do that on purpose or I don't even know the whole history of that, But you know, astrophysics naming an acronym, Well, that's a whole podcast episode.
Yeah, it probably divides the psychology of physicists too, like some of them want to be known as mad scientists, and some of them want to be like, no, let's be sane exactly.
So now they can dig deep into their models and understand what's going on. What's fascinating is that none of the models that we have currently perfectly describe what we see. Like some of them are pretty good but fail in this aspect, and some of them are pretty good in other aspects but fail one part of it. So none of our astrophysics models for the accretion disc perfectly describe what we see, which gives us fuel to learn more about what's happening in the vicinity of these black holes.
Oh, pretty cool. And it's also significant because it's our black hole, right, Like, it's the one closest to us, it's the one that's basically at the center of our galaxy. We have some sort of ownership over it, I guess, right, or at least relationship.
Yeah, it's our little cozy neighborhood black hole. And as you say, it's changing. And what they're planning to do next is to turn on the event horizon telescope for longer and try to crunch the data more powerfully so they can make a movie of this black hole, so not just a picture, but like a movie where you can see it changing and bubbling and frothing.
Interesting. So five days of data is not enough to make a movie.
Five days of data is just an enough to make a picture, and which you really need are more telescopes even so you can get more data for the same moments, so you can resolve it and make it sharper without having to integrate over that as much time. When they took this picture, they're basically assuming that it's not changing, and that adds to some of the fuzz of the picture. But if instead you can get the same sharpness by adding more telescopes, then you can use shorter time windows to take each picture, and then you can get a movie.
That's pretty exciting because you know, everything's moving to a video, right, It's going to go from Instagram to TikTok now.
Although the data that they've collected is like eight petabytes of data per day as they were collecting it, which is the equivalent of one hundred million TikTok videos. So yeah, turning all these videos out.
Which is how many TikTok videos get made an hour, right, so no problem.
And most of them have dogs and cats and horses in them anyway.
All right, Well, pretty exciting news and pretty amazing, I guess milestone for humanity to take a picture of the black hole of the center of our galaxy and to like see it and confirm that it's there, and to confirm all these incredible theories that had so far just been in people's heads.
Kind of right, Yeah, it's really exciting to see these things in reality. You know, you have ideas for how the universe is working, for what should be going on, but until you go out there and look, you don't know. And sometimes the universe comes back and tells you, oh, yeah, it's exactly what you thought it was. And sometimes the universe comes back and says, oh, you silly human it's secret. Option See, so this time I told us, yeah, it's a black hole and it's just the way you thought. And that's also exciting.
Yeah, it's exciting, even if it means Einstein was right.
Sorry, Daniel, exactly, Einstein was right again.
Go get your free donut.
You'll feel better, that's right. But I'm still here to eat donuts and he's not. Aha, Einstein, check meate Einstein.
Yeah, for how long? We'll see If you keep eating it too any donuts, he'll beat you in lifespan.
Probably exactly. My theory of lifespan is is you have a limited number of donuts. When you've eating them all, you're done.
Well, you'll have to go into a black hole to get more medio.
Or I'll have to eat a black hole sleevered donut.
All right, Well, we hope you enjoyed that, and we hope that you go out there and learn more about this incredible discovery. Thanks for joining us, See you next time.
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