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

0:08
Speaker 1: Hey, or hey, do you like a surprise candy center?
0:13
Speaker 1: It depends. Does it depend on what the surprise is? Absolutely,
0:18
Speaker 1: you know if it do leg yes, sign me up.
0:20
Speaker 1: If it's like marshmallow, I know. Thanks, Well, I guess
0:23
Speaker 1: that makes sense. Yeah. Also it depends on what is
0:26
Speaker 1: it surrounded by, Like what is it the center of?
0:28
Speaker 1: Like I don't want to surprise candy center in my
0:30
Speaker 1: taco or pizza. How about a surprise guacamole center in
0:35
Speaker 1: your taco? You mean like candy guacamole. I'm not so
0:40
Speaker 1: sure about that. How about candy guacamole in your dessert taco?
0:44
Speaker 1: Dessert taco? Now you're talking, can we put bananas in it?
0:48
Speaker 1: Banana avocado flavored ice cream? I'm not so sure. This
0:51
Speaker 1: was a great idea. Yeah, we went too far. Hi
1:09
Speaker 1: am r Hanmay, cartoonist and the creator of PhD comics. Hi,
1:12
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
1:15
Speaker 1: U c Irvine, and I will always try a weird
1:18
Speaker 1: flavor of ice cream. Really, have you tried a garlic
1:21
Speaker 1: ice cream? I have I tried garlic ice cream. I
1:24
Speaker 1: even tried pasta Fa Julie flavored ice cream. I've tried
1:27
Speaker 1: licorice ice cream. I've tried all the ice cream. Man,
1:30
Speaker 1: there's a lot happening in your laboratory there. I'm married
1:34
Speaker 1: to a biochemist. You know. She can really cook up
1:36
Speaker 1: some crazy stuff. That's long. She doesn't put a gut
1:39
Speaker 1: bacteria in your ice cream. That's what she researches, right,
1:42
Speaker 1: that's true. Well, there's that famous Nathan for You episode
1:45
Speaker 1: about poop flavored ice cream. What somebody made that? Or
1:49
Speaker 1: somebody made that accidentally. No, there's a company apparently which
1:53
Speaker 1: will create any flavor for you. So they created artificial
1:55
Speaker 1: poof flavored ice cream and just to see if people
1:58
Speaker 1: would try. Oh boy, let me try to are in
2:00
Speaker 1: flavored ice cream. No, I haven't been able to find
2:03
Speaker 1: that yet. Well, there you go. That's not too far
2:05
Speaker 1: from from some of these extreme flavors. But welcome to
2:10
Speaker 1: our podcast Daniel and Jorge Explain the Universe, a production
2:13
Speaker 1: of I Heart Radio in which we take a deep
2:15
Speaker 1: bite of the universe, hoping to enjoy its flavor. Whether
2:18
Speaker 1: it tastes like black holes or neutron stars, or swirling
2:21
Speaker 1: masses or tiny little particles, we are here to savor
2:25
Speaker 1: it with you. Because we want to know what the
2:27
Speaker 1: truth is out there in the universe, regardless of how
2:30
Speaker 1: it tastes, and so we don't shy away from taking
2:33
Speaker 1: a bite of any of the biggest questions in the universe.
2:37
Speaker 1: Where does the universe come from? What does it all mean,
2:39
Speaker 1: what's really going on on the tiny quantum scale, what's
2:43
Speaker 1: swirling around in the center of our galaxy? How does
2:46
Speaker 1: it all fit together? We talked about any end all
2:48
Speaker 1: of those questions and explain them to you. Yeah, because
2:51
Speaker 1: it is a wonderful and tasty universe. Now, Daniel, do
2:54
Speaker 1: you think we were taking bites out of the universe
2:56
Speaker 1: or are we just licking it before it melts? What
2:59
Speaker 1: is the neiver is going to drip onto in this analogy?
3:02
Speaker 1: That's my question. You know, a universe cone obviously hopefully
3:06
Speaker 1: a waffle cone. Maybe physics is like the napkin because
3:09
Speaker 1: we're trying to wipe up the messes. I see you're
3:11
Speaker 1: not trying to create the messes. I thought I thought
3:14
Speaker 1: physics was like the tongue doing the licking. I don't know,
3:16
Speaker 1: this is getting very strange. We are definitely mixing our
3:19
Speaker 1: metaphors here. But you know, the universe is delicious. The
3:22
Speaker 1: thing that I love about physics is that every time
3:25
Speaker 1: we do take a bite out of the universe, we
3:27
Speaker 1: find something amazing. It's pretty rare that you uncover some
3:30
Speaker 1: mystery and then go yawn, that was boring, And the
3:33
Speaker 1: universe has lots of impressive surprises for us. Yeah, even
3:37
Speaker 1: I hear it. It has Higgs boson flavored ice cream
3:40
Speaker 1: and also some cork ice cream as well. Or is
3:43
Speaker 1: all ice cream cork ice cream? Everything is cork flavor.
3:46
Speaker 1: That's right. In the end. The corks are the fundamental
3:49
Speaker 1: basis of flavor. And of course we do have flavor physics,
3:53
Speaker 1: which talks about different kinds of corks, but totally ignores
3:56
Speaker 1: the question of what they taste. Like, oh boy, we're
4:00
Speaker 1: getting inception here. We're like going down a few levels.
4:03
Speaker 1: It deploring the flavor of the particles that makeup flavor.
4:06
Speaker 1: That's right. And you know it's not just stuff here
4:08
Speaker 1: on Earth that you can taste. Astronauts report that space
4:11
Speaker 1: itself has a flavor. What what do you mean? It
4:15
Speaker 1: tastes like a vacuum. We talked about one time on
4:18
Speaker 1: the podcast here when you come back in from a
4:20
Speaker 1: spacewalk there are little volatile molecules from space that have
4:23
Speaker 1: stuck to your space suit, and when you enter the
4:26
Speaker 1: atmosphere they boil off and smell like barbecue. And sometimes
4:30
Speaker 1: people say, like a raspberry? Whoa really? Like? I guess
4:34
Speaker 1: there's like little tiny particles floating in space of raspberry
4:37
Speaker 1: and possibly barbecue. Yeah, and some of the gas clouds
4:40
Speaker 1: near the center of our galaxy are supposed to smell
4:43
Speaker 1: a little bit like cranberry, though nobody's ever been there.
4:47
Speaker 1: It's not raisins. Now, are you sure when they came
4:50
Speaker 1: in from the spacewalk the barbecue they're smelling is not
4:52
Speaker 1: themselves from being out out in the sun too long. Geez,
4:56
Speaker 1: smells like my hair is on fire. What's going on?
4:59
Speaker 1: It smells a cosmic ray fire. But anyway, it is
5:02
Speaker 1: a pretty interesting and amazing universe, and there's still a
5:05
Speaker 1: lot we don't know about it, even in our own neighborhood.
5:08
Speaker 1: There are big mysteries in our solar system and especially
5:10
Speaker 1: in our galaxy. Our galaxy is called the Milky Way,
5:13
Speaker 1: and it's big and it's amazing, has millions of stars,
5:16
Speaker 1: but there is a big mystery at the center of it.
5:18
Speaker 1: Because remember that everything we know about the universe and
5:21
Speaker 1: our galaxy comes from observations we have just made from
5:25
Speaker 1: here on Earth. Yeah, we've sent a few probes, maybe
5:28
Speaker 1: to the edge of our solar system, but mostly we
5:30
Speaker 1: have one eyeball trapped here in one spot in the galaxy,
5:34
Speaker 1: and we're trying to do something very difficult, which is
5:37
Speaker 1: make a map of the whole galaxy, of the whole universe,
5:40
Speaker 1: having seen it from just one spot. Imagine standing on
5:43
Speaker 1: the top of a mountain and then trying to make
5:45
Speaker 1: a map of the Earth. Some things are obscured from
5:48
Speaker 1: your view. Other things you have to just sort of
5:50
Speaker 1: sketch because you can't quite make them out. That's the
5:53
Speaker 1: challenge we face in trying to map out the cosmos
5:55
Speaker 1: around us. Yeah, it's pretty amazing how well we've done,
5:58
Speaker 1: you know, just from standing in that mount ten with
6:00
Speaker 1: a telescope, we've been able to basically figure out most
6:03
Speaker 1: of what the universe looks like, and how it's structured together,
6:06
Speaker 1: and how many stars there are out there, how many galaxies.
6:09
Speaker 1: But there are things that we can quite see from
6:11
Speaker 1: our point of view. Yes, sometimes we can be very
6:13
Speaker 1: direct and say, look, we see that thing. We know
6:15
Speaker 1: exactly what it is and where it is. Other times
6:18
Speaker 1: we have to sort of infer what we think is
6:21
Speaker 1: going on based on more indirect evidence, and that's how
6:24
Speaker 1: we've leveraged our powers of observation to tell us about
6:28
Speaker 1: how things look in places that we can't see. We
6:30
Speaker 1: have to make these indirect conclusions. But sometimes we might
6:34
Speaker 1: make mistakes because we might be folding in incorrect assumptions
6:38
Speaker 1: or guesses about what might be there. And people can
6:40
Speaker 1: come along with new ideas that give us new perspectives
6:43
Speaker 1: on what's going on. Yeah, you could be linking the
6:46
Speaker 1: wrong ice cream where all we know right there is
6:48
Speaker 1: no wrong ice cream. Man, We'll wait until you taste
6:52
Speaker 1: during ice cream or that poop ice cream that sounds
6:55
Speaker 1: like the wrong kind of ice cream. But yeah, it's
6:58
Speaker 1: a pretty mysterious galaxy that we live in. And so
7:00
Speaker 1: today we'll be tackling a question related to what's at
7:03
Speaker 1: the core of it. So on the podcast today we'll
7:06
Speaker 1: be asking the question, could our galaxy have a dark
7:13
Speaker 1: matter center? Mm? Hmm? Could our galaxy have a dark
7:18
Speaker 1: matter center? Now? Isn't dark matter all over the galaxy
7:21
Speaker 1: like it's in most of our galaxy made of dark matter. Yes,
7:24
Speaker 1: most of the mass in the galaxy is dark matter,
7:27
Speaker 1: and there is definitely dark matter hanging out at the
7:30
Speaker 1: center of the galaxy. But conventional wisdom is that the
7:33
Speaker 1: center of the galaxy also has a supermassive black hole
7:38
Speaker 1: as a like gravitational anchor something that's really holding the
7:42
Speaker 1: whole galaxy together, this incredibly massive object four million times
7:46
Speaker 1: the mass of the Sun. But we've never seen that
7:49
Speaker 1: black hole directly, and so some people wonder if it's
7:52
Speaker 1: really there or if instead it's dark matter doing the work.
7:56
Speaker 1: Interesting and yeah, because I guess we can't sort of
7:59
Speaker 1: look directly to the center of our galaxy. I mean,
8:01
Speaker 1: we can sort of look in the direction of the
8:03
Speaker 1: center of the galaxy, but it's so far away maybe,
8:05
Speaker 1: and there's so many things in between that it's hard
8:07
Speaker 1: to kind of see in there. It is, in fact
8:09
Speaker 1: completely obscured because the center of the galaxy is a
8:12
Speaker 1: busy place. There are a lot of stars between us
8:15
Speaker 1: and it, and there's also a lot of gas and dust,
8:18
Speaker 1: so it's not something that's very easy to look at
8:20
Speaker 1: directly in the visible light. And so we'll get into
8:23
Speaker 1: details of what we know about what's going on in
8:25
Speaker 1: the center of the galaxy. Why most astronomers think that
8:28
Speaker 1: there is a black hole there, and some new evidence
8:30
Speaker 1: that's casting doubt on that assumption. M I see. So
8:33
Speaker 1: the prevailing thought is that there is a supermassive black
8:36
Speaker 1: hole in the middle of our galaxy. But now the
8:38
Speaker 1: question is maybe there's not. Maybe it's just a whole
8:40
Speaker 1: bunch of super compact dark matter. Maybe. Yeah. In line
8:44
Speaker 1: with our podcast about dark stars, we are casting doubt
8:47
Speaker 1: on the existence of black holes everywhere. We are throwing
8:50
Speaker 1: shade on black holes because in the end, they are
8:53
Speaker 1: very difficult to see directly. It's always an inference. You're
8:56
Speaker 1: always jumping to a conclusion, saying there's a certain amount
8:59
Speaker 1: of mass and the certain amount of area, therefore it
9:02
Speaker 1: must be a black hole. But you know, that's not
9:04
Speaker 1: like finding the body in a murder. It's all circumstantial evidence. Yeah,
9:09
Speaker 1: And the problem with throwing shade at a black hole
9:11
Speaker 1: is that it never comes out. It just eats your
9:14
Speaker 1: shade and says, thank you, Can I have another. It's
9:17
Speaker 1: a pretty interesting question. What is at the center of
9:19
Speaker 1: our galaxy? Is it a supermassive black hole or is
9:22
Speaker 1: it dark matter? And so, as usual We were wondering
9:24
Speaker 1: how many people out there have thought about this question
9:26
Speaker 1: and think that maybe it could be dark matter. So
9:29
Speaker 1: Daniel went out there into the internet to ask people
9:31
Speaker 1: could our galaxy have a dark matter center instead of
9:34
Speaker 1: a black hole? So thank you very much to our
9:37
Speaker 1: cadre of volunteers. If you'd like to join them, please
9:40
Speaker 1: don't be shy, just email me two questions at Daniel
9:42
Speaker 1: and Jorge dot com. You know you want to, so
9:45
Speaker 1: think about it for a second. Do you think our
9:46
Speaker 1: galaxy has a dark matter center? Here's what people had
9:50
Speaker 1: to say. There is lots of evidence for a black
9:53
Speaker 1: hole from a high concentration of mass at the center
9:56
Speaker 1: of our galaxy because of the orbit of several star
10:00
Speaker 1: ours that are have been whipping around something very very small,
10:04
Speaker 1: very very fast. So that implies a density of matter
10:10
Speaker 1: foreign excess what we normally would predict for dark matter,
10:15
Speaker 1: and if the dark matter were to concentrate to that extent,
10:19
Speaker 1: it would then just become a black hole, since it
10:23
Speaker 1: is only gravity that matters. Anyway, I don't know why
10:26
Speaker 1: our galaxy would have a dark matter center instead of
10:29
Speaker 1: a black hole. I know that most galaxies do have
10:32
Speaker 1: a black hole at their center, as do most spots
10:35
Speaker 1: wear enough mass has just gotten together and hung out
10:37
Speaker 1: for long enough. Maybe it could be both. Could our
10:40
Speaker 1: galaxy have dark matter center instead of black hole? And
10:45
Speaker 1: I think we have a super massive black hole center
10:50
Speaker 1: of our galaxy, not dark matter. I don't really see
10:56
Speaker 1: how we could have a dark matter only center of
10:58
Speaker 1: our galaxy because would mean that all the regular matters
11:02
Speaker 1: being pulled into it, which in my head, would make
11:04
Speaker 1: it a black hole. Whether or not the dark matter
11:07
Speaker 1: falls into the black hole, it's kind of irrelevant because
11:09
Speaker 1: you've got a black hole there anyway, pulling in any
11:11
Speaker 1: barrionic matter. I do think that the galaxy can have
11:15
Speaker 1: the dark matter center because dark matter experiences gravity, it
11:20
Speaker 1: has it has mass, and it definitely experiences gravity. It
11:24
Speaker 1: accounts for like a very large amount of matter that
11:29
Speaker 1: we know, so we only know that normal matter is
11:32
Speaker 1: very less. And yeah, there is a possibility that there
11:35
Speaker 1: is a huge quantity of dark matter at the center
11:39
Speaker 1: of our galaxy instead of having a black hole. Turcky, Turcky.
11:45
Speaker 1: I have no idea, but it reminds me of something
11:48
Speaker 1: in in a video game I used to play. I'm
11:51
Speaker 1: just gonna leave this one as a shrug. All right,
11:54
Speaker 1: it seems that people are skeptical. Yeah, there's some great
11:57
Speaker 1: answers here. People thinking about what would happen to the
11:59
Speaker 1: dark matter if it got concentrated at the center of
12:02
Speaker 1: the galaxy. Really some great stuff. Yeah. I like the
12:04
Speaker 1: people who say it could be both, Like, yeah, why
12:06
Speaker 1: can't it have both both a super massive black hole
12:10
Speaker 1: and dark matter in it? Or how about a how
12:12
Speaker 1: about a dark matter black hole? A dark matter black
12:15
Speaker 1: hole be super awesome, Although you know, once material falls
12:19
Speaker 1: into the black hole, it's not really clear what its
12:21
Speaker 1: nature is anymore. Is it's still dark matter? Is it
12:24
Speaker 1: gotten converted into energy? Has got turned into something else?
12:28
Speaker 1: So once you're inside the black hole, it's just stuff. Man?
12:31
Speaker 1: WHOA yeah, because I guess dark matter could technically turn
12:34
Speaker 1: into regular stuff. Do you think it's made out of
12:36
Speaker 1: the same kind of like energy. We don't know, right,
12:38
Speaker 1: there might be some way for dark matter to turn
12:41
Speaker 1: into normal matter. We do know that there was a
12:43
Speaker 1: lot more dark matter in the early universe than there
12:45
Speaker 1: is today, and so we hypothesize that there's some mechanism
12:48
Speaker 1: by which dark matter can very slowly turn into normal matter.
12:52
Speaker 1: But it needs a lot of energy density for that
12:54
Speaker 1: to happen. So we think it might have happened in
12:56
Speaker 1: the early universe and then frozen out, and it might
12:59
Speaker 1: then again and have an inside black holes. Who knows,
13:02
Speaker 1: maybe threw a lot of shade to the black holes
13:05
Speaker 1: and lost some of its energy. All right, Well, let's
13:07
Speaker 1: tackle this question. Could it be dark matter at the
13:10
Speaker 1: center of our galaxy and not a supermassive black hole? Now,
13:13
Speaker 1: first of all, I guess why did we think or
13:15
Speaker 1: do we think that the center of our galaxy has
13:17
Speaker 1: a supermassive black hole. Well, let's not be too click baity. Definitely,
13:21
Speaker 1: the mainstream astronomy community is convinced that there's a supermassive
13:25
Speaker 1: black hole at the heart of our galaxy. I mean,
13:27
Speaker 1: they gave the twenty twenty Nobel Prize to two folks,
13:30
Speaker 1: Reinhard Genzel and Andrea Guz from u c l A,
13:34
Speaker 1: who've been observing the center of the galaxy for decades
13:37
Speaker 1: and trying to figure out what's going on there. But
13:39
Speaker 1: we've had a hint that there's something going on at
13:42
Speaker 1: the center of the galaxy for decades, since people sent
13:45
Speaker 1: up rockets into the upper atmosphere and heard this radio
13:49
Speaker 1: signal from the center of the galaxy. And then it
13:51
Speaker 1: was in the sixties and seventies that people figured out,
13:54
Speaker 1: oh wow, maybe this could be a black hole, and
13:57
Speaker 1: it was one of the first things identified as a
14:00
Speaker 1: black hole at the center of our galaxy. Mmmm. That's
14:03
Speaker 1: interesting because I think we talked about this in another
14:05
Speaker 1: episode where you know, we talked about how do we
14:08
Speaker 1: know there's maybe a black hole at the center of
14:09
Speaker 1: our galaxy? And I remember one of the ways is
14:11
Speaker 1: that you can tell from like how the stars around
14:14
Speaker 1: the center of the galaxy are moving, like they're moving faster,
14:18
Speaker 1: or their tighter orbits than you wouldn't have you didn't
14:21
Speaker 1: have a black hole. You can never see a black
14:23
Speaker 1: hole directly, right, It's just black. It's essentially invisible. So
14:27
Speaker 1: what you need to do to identify a black hole
14:29
Speaker 1: is to see its gravitational effect on stuff around it.
14:33
Speaker 1: And so the argument that something is a black hole
14:35
Speaker 1: is that you measure its mass by looking at how
14:38
Speaker 1: hard it pulls on things gravitationally nearby. But then the
14:41
Speaker 1: second crucial element is that you need to measure it's radius.
14:45
Speaker 1: Because not everything with gravity has a black hole, or
14:48
Speaker 1: the Earth has gravity. You can measure it's pull on
14:50
Speaker 1: the Moon doesn't make the Earth of the black hole.
14:52
Speaker 1: But if you can measure something's mass and it's radius
14:56
Speaker 1: and the radius is really really small, that means that
14:58
Speaker 1: the object is really dense, it's very compact, and below
15:02
Speaker 1: a certain radius, an object of that mass has to
15:05
Speaker 1: be a black hole as far as we know. Well,
15:07
Speaker 1: I so you're saying that we know that there is
15:08
Speaker 1: something really heavy at the center of our galaxy, is
15:11
Speaker 1: super duper heavy, but we don't know if it's actually
15:14
Speaker 1: a black hole. Like it could just be a giant
15:16
Speaker 1: ball of ice cream, right, it could be all that
15:19
Speaker 1: during and ice cream that people have been rejecting for
15:21
Speaker 1: all of those years. Yeah, nobody wants to lick yet.
15:24
Speaker 1: And so the tricky thing is the radius. And as
15:27
Speaker 1: you say, a great way to study this is to
15:29
Speaker 1: look at the effect on very close by stars, because
15:32
Speaker 1: they're mostly affected by the gravitational pull of this thing.
15:35
Speaker 1: And also as they pass close by, you can get
15:38
Speaker 1: a sense for how big the black hole is, because
15:41
Speaker 1: if something passes within one AU, for example, and survives,
15:45
Speaker 1: then you know that whatever is there has to have
15:47
Speaker 1: a radius of less than one AU, where a U
15:49
Speaker 1: is an astronomical unit, the distance from the Earth to
15:53
Speaker 1: the Sun. And that's exactly what they do, is they
15:55
Speaker 1: look at all the nearby stars. Is it's like a
15:57
Speaker 1: few stars that hang out really close to whatever this
16:00
Speaker 1: is at the center of the galaxy and they zip
16:02
Speaker 1: around it. So people look at the motion of those
16:05
Speaker 1: stars to try to measure the mass of this object,
16:07
Speaker 1: and they also look at the distance of closest approach
16:10
Speaker 1: to try to get a sense for what the radius
16:12
Speaker 1: of this thing might be. M So what you're saying
16:15
Speaker 1: that we can sort of look at the center of
16:16
Speaker 1: the galaxy, we can't see these stars orbiting around the
16:20
Speaker 1: very center of the Milky Way. Well, it's not easy
16:22
Speaker 1: and you can't see them invisible light, but infrared light
16:26
Speaker 1: can pass through a lot of the gas and the dust.
16:30
Speaker 1: So if you use filters on your telescope to only
16:32
Speaker 1: look through the infrared, you can see these stars. And
16:35
Speaker 1: in that way you can see what's going on in
16:38
Speaker 1: the center of the galaxy. And if you google you
16:40
Speaker 1: can watch these cool movies of these stars. And the
16:43
Speaker 1: movies take like more than a decade to make because
16:46
Speaker 1: these stars have like an orbital period of like sixteen years.
16:49
Speaker 1: But you can see them whooshing around this blank spot
16:52
Speaker 1: at the center of the galaxy, so it's really obvious
16:55
Speaker 1: that there's something very massive. They're interesting. So we do
16:58
Speaker 1: have sort of pictures of the center of the galaxy.
17:01
Speaker 1: You can s to c through that gas and dust,
17:03
Speaker 1: and it does show something pretty dense in the middle
17:05
Speaker 1: of it. That's right, So we can measure the mass
17:07
Speaker 1: pretty accurately to be about four million times the mass
17:11
Speaker 1: of our Sun. It's very very heavy. It's an incredible
17:14
Speaker 1: gravitational source. But the tricky thing is that we don't
17:17
Speaker 1: have a great measurement for the radius of this thing,
17:20
Speaker 1: because in order to measure the radius, something has to
17:22
Speaker 1: pass really really close and then survive, right, it has
17:25
Speaker 1: to like not fall into the black hole. There's a
17:27
Speaker 1: star that's called S two that goes really close to it.
17:30
Speaker 1: But the closest approach we've ever seen to this object
17:34
Speaker 1: is about twelve a U twelve times the distance between
17:38
Speaker 1: the Earth and the Sun. Wow, that that seems really
17:41
Speaker 1: small to me, right kind of right, like it's smaller
17:44
Speaker 1: than our solar system. Like this thing, whatever it is,
17:47
Speaker 1: the super dense thing at the center of the galaxy
17:50
Speaker 1: is smaller than our solar system. It is smaller than
17:52
Speaker 1: our solar system. But but it's four million times of
17:55
Speaker 1: the mass or sun. Four million times the mass of
17:57
Speaker 1: the Sun. But if you calculate how big should a
18:00
Speaker 1: black hole b, if it's four million times the mass
18:02
Speaker 1: of the Sun, then you can answer of like point
18:05
Speaker 1: one a U, like a tenth of an a U.
18:08
Speaker 1: So whatever this thing is, it's much smaller than sort
18:11
Speaker 1: of the radius we've been able to probe. Right, it
18:14
Speaker 1: might be a black hole that's really dense and at
18:16
Speaker 1: the heart of this sphere we haven't been able to
18:18
Speaker 1: see inside of yet. But that's the uncertainty. We don't
18:21
Speaker 1: really know if whatever this stuff is that has massive
18:24
Speaker 1: four million times the Sun is actually compactified enough to
18:28
Speaker 1: make a black hole, or if it's something else, something
18:30
Speaker 1: sort of larger and fluffier. Right, Like you could take
18:34
Speaker 1: four million times the mass of our sun in ice
18:36
Speaker 1: cream and put it in a giant ball, and probably
18:39
Speaker 1: would it be about that, you know, smaller than the
18:42
Speaker 1: size that we're observing. That could it be like you know,
18:44
Speaker 1: for a U, Yeah, twelve a U is a really
18:48
Speaker 1: large radius, and so it makes a huge volume. And
18:50
Speaker 1: so even though four million times the mass of the
18:53
Speaker 1: Sun is a lot of mass. If you spread it
18:55
Speaker 1: out through a sphere that's like twelve a U and radius,
18:58
Speaker 1: it's not actually that dense, So yeah, you don't have
19:01
Speaker 1: to be nearly as dense as a black hole. It's
19:03
Speaker 1: still a little bit denser than dury and ice cream,
19:05
Speaker 1: but you know, it's pretty close dense and flavor at least,
19:10
Speaker 1: all right, So that's kind of the mystery. We know
19:11
Speaker 1: there's something super heavy, four million times the mass of
19:14
Speaker 1: the Sun and in the center of our galaxy, but
19:16
Speaker 1: we don't know how dense it is, whether it's dense
19:18
Speaker 1: enough to be a black hole, or maybe it's just
19:20
Speaker 1: dense enough to be a big ball of ice cream
19:23
Speaker 1: or dust or cloud or who knows. So let's get
19:25
Speaker 1: into why would not be a black hole and what
19:28
Speaker 1: evidence we have for either answer. But first let's take
19:30
Speaker 1: a quick break, right, Daniel, we're asking the question what
19:45
Speaker 1: is at the center of our galaxy? And it could
19:47
Speaker 1: be a super massive black hole or it could be
19:50
Speaker 1: something else. All we know is that it's super heavy.
19:52
Speaker 1: It's four million times the mass of our Sun, and
19:54
Speaker 1: it's pretty small and smaller than our solar system, but
19:57
Speaker 1: maybe not small enough to be a black hole. So
19:59
Speaker 1: how did not be a black hole? Like, if you
20:01
Speaker 1: have that much mass four million times the mass of
20:03
Speaker 1: our Sun in that space, when it eventually collapse into
20:06
Speaker 1: a black hole anyways, Well, it depends a little bit
20:08
Speaker 1: on what it is. Right, Things don't always collapse into
20:12
Speaker 1: a black hole because they have ways of resisting that collapse.
20:14
Speaker 1: Like why doesn't this Sun collapse into a black hole immediately? Well,
20:18
Speaker 1: because it has fusion. That energy is pushing out and
20:21
Speaker 1: keeping the Sun fluffy. Why doesn't the Earth collapse into
20:23
Speaker 1: a black hole? Because of the strength of the materials, Right,
20:26
Speaker 1: they have this actual tensile strength to resist being crushed
20:30
Speaker 1: by gravity. And as things get denser and denser, they're
20:33
Speaker 1: all these thresholds to overcome. Like even neutron stars, which
20:36
Speaker 1: are crazy dense, are resisting collapse into a black hole
20:40
Speaker 1: because of the quantum degeneracy pressure. Like all these corks
20:44
Speaker 1: don't want to be on top of each other. And
20:46
Speaker 1: so in order to become a black hole, you have
20:48
Speaker 1: to have enough mass and already be compact enough to
20:50
Speaker 1: collapse to overcome all of these sort of thresholds. So
20:54
Speaker 1: it's possible to arrange this much mass in that small
20:57
Speaker 1: space that doesn't collapse into a black hole. Mmmmm, but
21:01
Speaker 1: I guess you know, if you had four million times
21:03
Speaker 1: the mass of our Sun in it, and if it
21:05
Speaker 1: was just gas or does wouldn't you know? Don't we
21:08
Speaker 1: have models that say what would happen to something like that,
21:10
Speaker 1: Like if it had fusion keeping it from collapsing to
21:13
Speaker 1: a black hole, we it would be shining and we
21:14
Speaker 1: would see it, right m m yeah, So clearly it's
21:17
Speaker 1: not shining. But there's also questions about like velocity. If
21:20
Speaker 1: something is swirling really really fast, then it's hard for
21:23
Speaker 1: it to collapse. That's why, for example, dark matter doesn't
21:26
Speaker 1: collapse into a black hole because dark matter has a
21:29
Speaker 1: lot of rotational energy. It's swirling around the center of
21:33
Speaker 1: the galaxy, and in order for it to collapse into
21:35
Speaker 1: a tiny point, it needs to lose some of that
21:38
Speaker 1: angular momentum, right, and angler momentum is conserved in our universe,
21:42
Speaker 1: So the only way to lose angular momentum is to
21:44
Speaker 1: like bump into something else and give your angular momentum away.
21:47
Speaker 1: And that's really difficult for dark matters to do because,
21:50
Speaker 1: as we've talked about before, it's not sticky, So it's
21:53
Speaker 1: possible that whatever is there is just swirling around for
21:55
Speaker 1: a while. But there are also other explanations, and people
21:58
Speaker 1: have a very specific theory for what could be at
22:01
Speaker 1: the center of the galaxy that's resisting this collapse and
22:04
Speaker 1: has the same mass. Well, again, maybe let's take a
22:07
Speaker 1: step back. You said the prevailing theory is that it
22:10
Speaker 1: is a black hole. So what makes people think that
22:12
Speaker 1: it is a black hole if we don't really have
22:14
Speaker 1: direct evidence of it. I guess it's just the leading candidate,
22:17
Speaker 1: you know, of the things that could have that mass
22:19
Speaker 1: and that radius and not give off any direct light,
22:22
Speaker 1: a black hole is sort of the least exotic. You
22:25
Speaker 1: can't come up with other things, but usually they require
22:28
Speaker 1: inventing new particles, things that we haven't discovered yet. So
22:31
Speaker 1: there's no way to arrange like normal matter as far
22:34
Speaker 1: as we know, into a configuration like that that's going
22:37
Speaker 1: to be stable and last a long time and not
22:39
Speaker 1: collapse into a black hole. Like even a big swirling
22:41
Speaker 1: cloud of gas that's spinning and resisting falling into a
22:44
Speaker 1: black hole eventually will collapse into a black hole because
22:48
Speaker 1: they'll bump against itself and lose its angular momentum. So
22:51
Speaker 1: you need some sort of like new kind of particle.
22:53
Speaker 1: I see. So, as far as we know, if you
22:55
Speaker 1: did have a giant ball of ice froam that big,
22:57
Speaker 1: it would sort of collapse into a black hole eventually, Yes, exactly,
23:00
Speaker 1: would be a Durian flavored black hole. Yeah, and that
23:03
Speaker 1: one you don't want to lick. I feel like we're
23:06
Speaker 1: going to get so much hate mail from Duryan lovers
23:09
Speaker 1: out there. Don't write his hate mail until you've actually
23:12
Speaker 1: tasted during an ice cream and can vouch for its deliciousness.
23:16
Speaker 1: All right, So then that's the leading candidate, because any
23:18
Speaker 1: other explanation requires a new theory or a new particle
23:21
Speaker 1: or something super exotic. You know, as far as we know,
23:23
Speaker 1: the universe dictates that something that big would fall into
23:27
Speaker 1: a black hole. So that's kind of why we think
23:29
Speaker 1: there is a black hole. It is, and it was
23:31
Speaker 1: very widely accepted until recently. What happened, Well, there's this
23:35
Speaker 1: really cool astronomical experiment. You know, astronomers don't get to
23:38
Speaker 1: do what particle physicists do, which is like design collisions.
23:42
Speaker 1: I get to like, say, I'm going to smash a
23:43
Speaker 1: proton into an electron or let's try shooting muans at
23:47
Speaker 1: this thing and see what happens. Astronomers don't get to
23:49
Speaker 1: do that. They don't get to build colliders and smash
23:52
Speaker 1: two black holes together. They just have to wait for
23:54
Speaker 1: stuff to happen in the universe in a place that
23:56
Speaker 1: they can observe it. So they have to get lucky.
23:59
Speaker 1: And about ten years ago, people realized that there was
24:02
Speaker 1: this huge cloud of gas called G two which was
24:06
Speaker 1: headed for the black hole. It was going to make
24:09
Speaker 1: a really close approach in our galaxy or in another galaxy.
24:12
Speaker 1: In our galaxy. It was heading right for the center
24:15
Speaker 1: of our galaxy. It was gonna make a near miss
24:18
Speaker 1: of the black hole. And they thought this would be
24:20
Speaker 1: really cool because it allows them to really study the
24:22
Speaker 1: black hole in a new way. Let's throw something at
24:25
Speaker 1: it and see what happens, right, and let them test
24:28
Speaker 1: the details of this encounter between the gas cloud in
24:32
Speaker 1: the black hole. So you could see this gas cloud
24:34
Speaker 1: like you can see it through the PLoud of gas
24:37
Speaker 1: in the center of the galase. You can see it
24:39
Speaker 1: like that. There was one nearby. Yeah, you can see
24:41
Speaker 1: X rays coming out of this thing. And so you
24:43
Speaker 1: can watch this cloud of gas and everybody got really
24:46
Speaker 1: excited because they were not sure what's going to happen.
24:49
Speaker 1: It sort of reminds me of when everybody saw that
24:51
Speaker 1: comment that was going to smash into Jupiter, Like we
24:54
Speaker 1: saw a comment coming into the Solar system, and then
24:55
Speaker 1: people calculate its trajectory and they're like, oh, yeah, it's
24:58
Speaker 1: gonna hit Jupiter like citing. Yeah, it's exciting unless you
25:02
Speaker 1: live in Jupiter. If you just bought real estate and Jupiter,
25:05
Speaker 1: I'm sorry your investment is a waste. But you know,
25:08
Speaker 1: astronomical collisions are a great way to learn about stuff.
25:11
Speaker 1: So people get really excited. And just like seven years
25:14
Speaker 1: ago or so, and they had all these calculations for
25:17
Speaker 1: what they expected to happen when this gas cloud passed
25:20
Speaker 1: near the black hole. Interesting like sprinkling dust into a
25:24
Speaker 1: swirling toilet bowl, right, kind of like what's gonna happen
25:27
Speaker 1: to it? Is it gonna stay together or is it
25:30
Speaker 1: gonna gonna get shredded apart? Yeah, And the calculation suggested
25:33
Speaker 1: that this thing should be totally shredded. I mean, a
25:35
Speaker 1: gas cloud is not really held together very tightly. It's
25:38
Speaker 1: just a big loose cloud of gas. And what happens
25:41
Speaker 1: when you get near a black hole is that there
25:43
Speaker 1: are huge tidal forces. Right. Remember, tidal forces are gravity
25:47
Speaker 1: trying to pull you apart, because if part of you
25:49
Speaker 1: it's closer to the black hole than another part, then
25:52
Speaker 1: the part that's closer is getting pulled on harder than
25:55
Speaker 1: the rest of you, And so the gravity essentially is
25:57
Speaker 1: trying to pull you apart because it's pulling on bits
25:59
Speaker 1: of you with different forces. So they expected that when
26:02
Speaker 1: this gas cloud came close to the black hole, it
26:05
Speaker 1: would be totally shredded by these title forces. But wait,
26:08
Speaker 1: how close did it get? Like I thought, we could
26:11
Speaker 1: only see up to like twelve AU. That's the closest
26:14
Speaker 1: that anything has ever come to the black hole. This
26:16
Speaker 1: gas cloud wasn't going to get that close. It was
26:19
Speaker 1: going to approach like a couple hundred a U, but
26:22
Speaker 1: close enough that you could get some information about the
26:25
Speaker 1: black hole. You know, you can get some like distant
26:27
Speaker 1: information about the black hole just by measuring the gravitational
26:30
Speaker 1: effect on nearby stuff. You can measure, for example, like
26:33
Speaker 1: the slope with a gravitational field. Right, but at that
26:36
Speaker 1: far away, wouldn't a black hole act the same way
26:39
Speaker 1: as a giant ball of ice cream. Yeah. Absolutely. If
26:42
Speaker 1: you stay outside of the heavy object at the center
26:44
Speaker 1: of the galaxy, then you can't tell the difference gravitationally
26:48
Speaker 1: between a black hole or a ball of ice cream
26:51
Speaker 1: or a giant space taco. As long as it has
26:53
Speaker 1: four million solar masses, they would all have the same
26:56
Speaker 1: gravity from the outside. You're absolutely right. So you can't
27:00
Speaker 1: use a gas cloud at like hundreds of AU to
27:02
Speaker 1: help understand what's going on inside the twelve AU radius
27:06
Speaker 1: where we think there's a black hole. But what if
27:09
Speaker 1: it's not actually a black hole, and what if it's
27:12
Speaker 1: not actually contained within the twelve AU What if it's
27:16
Speaker 1: something else much larger and fluffier, bigger than the twelve AU.
27:20
Speaker 1: If it's a big, fluffy mass that's hundreds of a
27:23
Speaker 1: U yde with a very very dense core, then it
27:26
Speaker 1: could still look like a black hole to the stars
27:29
Speaker 1: orbiting at twelve AU, but it would have a very
27:31
Speaker 1: different effect on the gas cloud. So I talked to
27:34
Speaker 1: Grant Weldon. He's an astrophysics grad student at u c
27:37
Speaker 1: l A who actually works in Professor Guests group. She's
27:40
Speaker 1: the recent Nobel lawyer who studies the center of the galaxy.
27:43
Speaker 1: He said, think of it like a fog that all
27:46
Speaker 1: the objects in the galactic center sit in. The idea
27:49
Speaker 1: is that if it's not a black hole concentrated within
27:52
Speaker 1: that twelve AU, but instead some bigger, more extended mass
27:56
Speaker 1: larger than the twelve AU, then it wouldn't have the
27:59
Speaker 1: same time tidal force effect on the cloud because the
28:02
Speaker 1: gas cloud G two would be passing partially inside this
28:06
Speaker 1: new fluffy blob. So the title force calculations that assume
28:10
Speaker 1: a big mass within the twelve au would be wrong.
28:12
Speaker 1: But I guess the point is that this gas cloud
28:14
Speaker 1: survived like it didn't get shredded as if it would
28:17
Speaker 1: if there was a black hole in the middle of
28:19
Speaker 1: the galaxy. Yeah, everybody was expecting this thing to get
28:21
Speaker 1: totally torn apart by this black hole or whatever is there.
28:25
Speaker 1: But instead it derived. It passed right by, and it
28:27
Speaker 1: mostly held its shape. You know, it got a little
28:30
Speaker 1: bit twisted up, but it was not totally pulled apart
28:33
Speaker 1: the way that you would expect for a gas cloud
28:35
Speaker 1: passing by this massive gravitational object. So that was a
28:39
Speaker 1: real mystery. People were like, hold on a second, what's
28:42
Speaker 1: going on. This isn't described at all by our calculations. Wow,
28:47
Speaker 1: maybe the gas cloud was made out of drain and
28:49
Speaker 1: the black hole was like, I don't want any I
28:51
Speaker 1: don't want to lick. This thing totally explains it. Break
28:55
Speaker 1: when you're getting rejected by clouds of gas, Wow, you
28:58
Speaker 1: must really be stinky. So then that threw some shade
29:02
Speaker 1: on the theory that maybe there's a black hole at
29:04
Speaker 1: the center of the galaxy, like, maybe it's not a
29:06
Speaker 1: black hole exactly. People start to think, maybe we should
29:08
Speaker 1: consider some alternatives. Are there other ways we can explain
29:12
Speaker 1: what happened to this gas cloud other than a black hole,
29:15
Speaker 1: because that would be then consistent with all of our observations.
29:19
Speaker 1: And that's when people started drilling into this question of
29:21
Speaker 1: how well do we know the density of this object?
29:24
Speaker 1: Is it possible that there's something actually much larger they're
29:28
Speaker 1: not actually a black hole, but something really much more extended,
29:31
Speaker 1: fluffier and broader and not actually a black hole. Interesting? Right, Yeah,
29:36
Speaker 1: I guess everyone just assumed this was a black hole,
29:38
Speaker 1: but now you have this evidence that maybe may people go,
29:41
Speaker 1: await a minute, how do we actually know that? Yeah?
29:43
Speaker 1: And so people have been creative and there's this really
29:45
Speaker 1: fun theory of a new kind of dark matter. It's
29:48
Speaker 1: called the dark nose. So this would be little particles
29:52
Speaker 1: that make up dark matter. They call them darky nose,
29:55
Speaker 1: and these are fermions, and fermions are a kind of
29:59
Speaker 1: fundamental particle. They're sort of like electrons and quarks. They
30:02
Speaker 1: have this really important property that they don't like to
30:05
Speaker 1: be on top of each other. They don't like to
30:07
Speaker 1: share the same state, you know how Electrons, for example,
30:10
Speaker 1: if you put one around an atom, it fills up
30:12
Speaker 1: a state, and you put another one there, it can't
30:14
Speaker 1: go into the same energy level, has to go into
30:16
Speaker 1: the next one. That's because their fermions, they don't like
30:19
Speaker 1: to ever occupy the same quantum states. The idea is
30:22
Speaker 1: that these dark matter particles, these dark enos, are fermions,
30:26
Speaker 1: so they can coalesce gravitationally, but they resist collapsing into
30:30
Speaker 1: a black hole because of this quantum degeneracy pressure, this
30:34
Speaker 1: polity exclusion principle that keeps them from getting too dense.
30:37
Speaker 1: WHOA wait a minute, you're saying, maybe it's not a
30:40
Speaker 1: black hole, and so therefore your go to explanation is
30:43
Speaker 1: to invent a totally new kind of matter. Another new
30:47
Speaker 1: kind of matter, Like, are there other explanations using regular
30:49
Speaker 1: matter that could explain this giant ball of stuff in
30:52
Speaker 1: the middle of our galaxy. Well, we talked about a
30:54
Speaker 1: few minutes ago. Any kind of normal matter is going
30:57
Speaker 1: to eventually coalesced into a black hole, and whatever is
31:00
Speaker 1: there has been there for a long long time, and
31:02
Speaker 1: so it would have time to collapse into a black hole.
31:05
Speaker 1: So you need something which has a new property of
31:08
Speaker 1: not collapsing into a black hole. So you have to
31:11
Speaker 1: give it this like you know, quantum de generously pressure
31:13
Speaker 1: or something in order for it to survive this crushing gravity.
31:17
Speaker 1: Didn't you mentioned like a neutron star maybe, or some
31:20
Speaker 1: other kind of dense object. Neutron stars can only be
31:23
Speaker 1: up to like two times the mass of the Sun.
31:26
Speaker 1: If it gets any bigger than they collapse gravitationally. So
31:29
Speaker 1: this thing is four million times the mass of the Sun.
31:32
Speaker 1: Neutron stars are a really very special case of avoiding
31:36
Speaker 1: a black hole. But if it's two million neutron stars
31:39
Speaker 1: kind of orbiting around each other like a beehive, you know,
31:43
Speaker 1: like I guess that would also eventually collapse to it
31:46
Speaker 1: would also eventual collapse and neutron stars are not black, right,
31:49
Speaker 1: they do emit. They're super hot and they glow. They
31:52
Speaker 1: emit X rays and they spin also, and we can
31:55
Speaker 1: actually see hot spots on the surface of neutron stars
31:58
Speaker 1: because they emit X rays. Is a telescope on the
32:00
Speaker 1: International Space Station called the Nicer Telescope, which looks just
32:04
Speaker 1: at those kind of objects. So in order to explain
32:07
Speaker 1: this like maybe new fuzzy fluffy stuff at the center
32:11
Speaker 1: of the galaxy, they had to use these new particles
32:14
Speaker 1: with this special property. Okay, So so then you're saying,
32:17
Speaker 1: this possible explanation for this heavy mass that's maybe not
32:20
Speaker 1: a black hole at the center of the galaxy. So
32:22
Speaker 1: it's a dark matter. But now you're sort of positing
32:25
Speaker 1: what dark matter is, and you're saying dark matter is
32:27
Speaker 1: maybe made out of a certain particle called the dark keynote. Yeah,
32:30
Speaker 1: and this would give dark matter the property that it
32:32
Speaker 1: needs to avoid collapsing into a black hole once it's
32:36
Speaker 1: already gotten into this little area of twelve a U
32:39
Speaker 1: and having four million times in the mass of the Sun. Right,
32:43
Speaker 1: because I think we talked about this in another episode,
32:45
Speaker 1: that dark matter can itself turn into a black hole, Like,
32:48
Speaker 1: if you get enough dark matter in a small enough space,
32:50
Speaker 1: it will create a dark matter black hole exactly, because
32:53
Speaker 1: anything can create a black hole that has mass. The
32:56
Speaker 1: cool thing about black holes and the cool thing about
32:58
Speaker 1: gravity is that they talked to anything that has mass,
33:01
Speaker 1: anything that has energy. So there are a really cool
33:03
Speaker 1: way to probe things in the universe that are otherwise
33:06
Speaker 1: totally invisible to us, that we might otherwise have no
33:10
Speaker 1: way to interact with. So if dark matter falls new
33:12
Speaker 1: black hole, it just adds to the mass of the
33:14
Speaker 1: black hole. It is challenging, however, to create a dark
33:17
Speaker 1: matter black hole, because it's hard to get dark matter
33:19
Speaker 1: that dense. Dark matter tends to be diffused, and it
33:22
Speaker 1: tends to be sort of fluffy, and it's hard to
33:24
Speaker 1: squeeze it down because there are no other interactions. It's
33:27
Speaker 1: not sticky like other kinds of matter. I see. So
33:31
Speaker 1: then you're saying the possible explanation is not really a
33:33
Speaker 1: new kind of matter. It's just like, maybe it's helping
33:36
Speaker 1: us pinpoint a specific property of dark matter that would
33:39
Speaker 1: allow it to become a dense black hole object without
33:42
Speaker 1: turning into a black hole. Sure, yeah, I think people
33:45
Speaker 1: in the dark matter community would say that this is
33:47
Speaker 1: a new kind of matter, and it's definitely not like
33:49
Speaker 1: the number one candidate for dark matter otherwise. And these
33:53
Speaker 1: particles are not like everybody's favorite dark matter theory, but
33:58
Speaker 1: they do have the properties you need that if you
34:00
Speaker 1: put them together and create this object of dark nose
34:02
Speaker 1: at the center of the galaxy, it's fluffy enough that
34:05
Speaker 1: it can explain why this gas cloud survived. I see,
34:08
Speaker 1: And it doesn't collapse into a black hole. You're saying
34:10
Speaker 1: because of its quantum properties, like it has this exclusion
34:14
Speaker 1: principle that lets it not collapse. Yeah, precisely. And you
34:18
Speaker 1: know it's a little bit cooked up, right. They created
34:20
Speaker 1: this idea. They've cooked up these dark he nose just
34:23
Speaker 1: to solve this problem. So it's not like something we
34:26
Speaker 1: otherwise already thought existed. We have good evidence for. Oh look,
34:30
Speaker 1: it also explains this, right, it's a little bit more descriptive.
34:33
Speaker 1: So you've always got to be a little bit more
34:35
Speaker 1: skeptical when somebody has cooked up a new idea just
34:38
Speaker 1: to explain one particular observation. Really, you've got to test
34:42
Speaker 1: it in other places. You've got to see like a
34:43
Speaker 1: symphony of results that are all telling you the same story. Yeah,
34:47
Speaker 1: I'm always skeptical when there's a physicist doing the cooking.
34:51
Speaker 1: So that's a possible explanation for what could be inside
34:54
Speaker 1: of the center of our galaxy. And let's get into
34:56
Speaker 1: what the answer is. What does the evidence say, is
34:58
Speaker 1: there a black hole at the center of our galaxy?
35:00
Speaker 1: Or could it be a big ball of this dark
35:03
Speaker 1: keno dark matter? But first, let's take another quick break.
35:18
Speaker 1: All right, what's at the candy center of our galaxy?
35:21
Speaker 1: Is it marshmallows? Is it? Is it guacamole? Or is
35:26
Speaker 1: it a new kind of dark matter called a dark
35:28
Speaker 1: keno which um ironically taste kind of like, how do
35:34
Speaker 1: you know what darkness tas like? I've been there, you know,
35:39
Speaker 1: they offer free samples. Alright, I'm packing my bags, let's go. So, yeah,
35:45
Speaker 1: we thought for a long time it was a black
35:46
Speaker 1: hole at the center of our galaxy, but maybe it's not.
35:49
Speaker 1: And so the only other thing that could explain it
35:51
Speaker 1: is something called dark keno, which is a kind of
35:54
Speaker 1: dark matter that doesn't collapse when it gets that compacted
35:57
Speaker 1: to What does the evidence say, Daniel, where's it thinking
35:59
Speaker 1: in the physics community. I think the physics community reacts
36:02
Speaker 1: to this idea like that's cute, but probably not. It
36:05
Speaker 1: hasn't really persuaded a lot of astronomers, And one reason
36:09
Speaker 1: is that it's not so easy to understand how you
36:11
Speaker 1: would make such a big ball of dark matter. As
36:14
Speaker 1: you've talked about a few times, dark matter is big,
36:17
Speaker 1: it's fluffy, it's diffused, it's swirling around the center of
36:20
Speaker 1: the galaxy, and so we don't know like how you
36:23
Speaker 1: would get it to collapse. Like if I gave you
36:25
Speaker 1: a serving of dark matter that had in the mass
36:27
Speaker 1: of four million sons, it wouldn't be easy for you
36:30
Speaker 1: to force it into that dense in area. So we
36:33
Speaker 1: have no story for how this thing could have formed, right,
36:36
Speaker 1: because as far as we know, dark matter is not
36:39
Speaker 1: very sticky or not sticky at all. Right, Like, if
36:41
Speaker 1: we have a bunch of dark matter in space, it's
36:43
Speaker 1: not gonna come together in clumb naturally. It's gonna get
36:47
Speaker 1: attracted to itself, but it's gonna keep flying past itself
36:50
Speaker 1: and keep flying past itself to the point where it
36:52
Speaker 1: would just be a fluffy cloud maybe forever. Yeah, And
36:55
Speaker 1: people have done simulations to test this and say, well,
36:58
Speaker 1: what if dark matter are these kind of dark eno fermions,
37:01
Speaker 1: and you have a big galaxy sized blob of them.
37:03
Speaker 1: What happens and you just don't get this kind of core.
37:06
Speaker 1: You don't get this like really dense ball in the center.
37:10
Speaker 1: That would explain the data. Now, if you happen to
37:12
Speaker 1: have that dense ball in the center of the galaxy,
37:15
Speaker 1: it can explain what happened to this gas cloud. But
37:18
Speaker 1: nobody understands how you would make such a dense blob
37:21
Speaker 1: of dark matter. It doesn't arise naturally in our simulations,
37:25
Speaker 1: I see. But these simulations are based on what we
37:27
Speaker 1: know about dark matter. But we don't really understand dark matter.
37:30
Speaker 1: So could dark matter have some sort of property we
37:32
Speaker 1: don't know about that would make it clump like that?
37:34
Speaker 1: It would need to have some sort of other self
37:36
Speaker 1: interaction right some way to get sticky, so that it
37:39
Speaker 1: tends to clump someone to like bump into itself and
37:42
Speaker 1: lose its angular momentum so it doesn't just orbit forever
37:45
Speaker 1: and it falls into itself somehow. But nobody has a
37:48
Speaker 1: theory of dark matter like that that's also consistent with
37:51
Speaker 1: everything else. You know, we're pretty sure that dark matter
37:54
Speaker 1: doesn't have a very strong interaction with itself. We've seen
37:57
Speaker 1: huge clouds of dark matter pass through each other, you know.
38:01
Speaker 1: The Bullet cluster, for example, was a collision of two
38:04
Speaker 1: huge galaxy clusters, each of which had a lot of
38:07
Speaker 1: dark matter, but the dark matter just passed right through
38:10
Speaker 1: itself to the other side. Even though there is some
38:12
Speaker 1: gravitational attraction between the two clouds of dark matter, that's
38:16
Speaker 1: really pretty weak. So we're pretty sure that dark matter
38:18
Speaker 1: does not have any very strong interactions with itself, and
38:22
Speaker 1: so it's really hard to explain how you would get
38:24
Speaker 1: a dense clump of dark matter at the center of
38:27
Speaker 1: the galaxy. Just like, no way to get it there, right,
38:29
Speaker 1: even if you give it these interesting quantum properties that
38:32
Speaker 1: it doesn't work out like you said, simulated, it still
38:35
Speaker 1: doesn't clump. But remember that also we have questions about
38:38
Speaker 1: how black holes form, right. We have a pretty good
38:41
Speaker 1: theory for why black holes conform at the center of galaxies,
38:44
Speaker 1: but we don't really understand how they got so big.
38:47
Speaker 1: So it's sort of a similar question. You know, if
38:49
Speaker 1: you simulate black hole formation in galaxies, they get big,
38:53
Speaker 1: but they don't get as big as the supermassive black
38:56
Speaker 1: holes that we see, So that's also an open questions.
38:59
Speaker 1: Just's just a lot we don't understand about how the
39:01
Speaker 1: centers of galaxies form, So you can criticize this theory
39:05
Speaker 1: for like, well, yeah, maybe that's what it's there, but
39:07
Speaker 1: how can you explain how it got there. We can't
39:10
Speaker 1: explain how black holes form at the center of these
39:12
Speaker 1: galaxies either, WHOA I see. So just because you can't
39:16
Speaker 1: explain how it got there doesn't mean it's not there.
39:19
Speaker 1: Because we don't know how the black hole. Even if
39:21
Speaker 1: it is a black hole, we don't know how the
39:22
Speaker 1: black hole got there. That means it could still be
39:25
Speaker 1: dark matter. It could still be dark matter. I think
39:27
Speaker 1: prevailing wisdom is still that is probably a black hole.
39:30
Speaker 1: And people have been creative and trying to find other
39:32
Speaker 1: ways to explain why the gas cloud wasn't torn up
39:35
Speaker 1: even if it is a black hole. Like Andrea Guez,
39:38
Speaker 1: the u c l A professor who won the know
39:39
Speaker 1: About prize, she suggested that maybe it's not actually just
39:42
Speaker 1: a gas cloud. Maybe inside this gas cloud there's like
39:45
Speaker 1: a string of stars that have the gravitational like strength
39:49
Speaker 1: to hold the gas cloud together, and that's why when
39:52
Speaker 1: it passed near this object. It wasn't actually torn to shreds.
39:55
Speaker 1: It has like more gravitational self consistency than people imagine.
40:00
Speaker 1: I see. Maybe that's why it didn't get treaded, Like
40:03
Speaker 1: it wasn't just my gas in that cloud. Yeah, and
40:05
Speaker 1: she has a very specific prediction for like a binary
40:08
Speaker 1: star system inside this gas cloud that could really hold
40:11
Speaker 1: it together so when it passes by, like keeps its consistency,
40:14
Speaker 1: it doesn't get pulled apart by the black hole. I see. Now,
40:18
Speaker 1: what about some of our listeners said that what if
40:20
Speaker 1: it's both, Like what if there's dark batter and the
40:23
Speaker 1: black hole in the center of our galaxy? Like, could
40:26
Speaker 1: it be a mixture of the two things, like some
40:28
Speaker 1: sort of super compact dark matter thing and maybe a
40:31
Speaker 1: black hole or not a black hole, or a bunch
40:33
Speaker 1: of intron stars or something like that. Yeah, it could
40:35
Speaker 1: basically be you know, all of the above, right, And
40:37
Speaker 1: remember the current theory, the prevailing wisdom is not just
40:40
Speaker 1: that it's only a black hole. We do think that
40:42
Speaker 1: there's a lot of dark matter at the center of
40:44
Speaker 1: the galaxy. We think that's the densest place to find
40:48
Speaker 1: dark matter in our galaxy is at the center. But
40:51
Speaker 1: the current thinking about the density of dark matter is
40:53
Speaker 1: that it's not that great, right, dark matter, there's a
40:56
Speaker 1: lot of it in the galaxy, but it's also spread
40:58
Speaker 1: out through space a lot more evenly than normal matter,
41:01
Speaker 1: because again, it doesn't clump. And so for example, in
41:04
Speaker 1: the volume of the Earth, we think there's like less
41:07
Speaker 1: than a kilogram of dark matter, like with less than
41:10
Speaker 1: one squirrels worth of dark matter. So there is almost
41:13
Speaker 1: certainly some dark matter at the center of the galaxy,
41:15
Speaker 1: and almost certainly some dark matter in that black hole
41:18
Speaker 1: if it exists, but it's not contributing significantly because it's
41:21
Speaker 1: not that dense. It's sort of spread out everywhere through
41:24
Speaker 1: the center of the galaxy. M m. Yeah, dark matter
41:27
Speaker 1: is pretty squirrely like that hard to catch. But we
41:30
Speaker 1: also see dark matter sort of clumping in our galaxy, right,
41:33
Speaker 1: Like dark matter is not a totally diffused cloud. It
41:35
Speaker 1: does sort of clump in the middle, but you're saying
41:37
Speaker 1: it doesn't clump enough to maybe explain what's going on. Yeah,
41:40
Speaker 1: what we're talking about here is like an enormous spike
41:43
Speaker 1: con density. Yes, dark matter is denser at the center
41:46
Speaker 1: of our galaxy, but this object, whatever it is, with
41:49
Speaker 1: four million times the mass of the Sun in a
41:51
Speaker 1: very small area is much denser than the typical dark
41:54
Speaker 1: matter density at the center. Yeah, it's four million sons
41:58
Speaker 1: basically in the space of our sources them. Yeah, that's
42:00
Speaker 1: a lot of ice cream. It's a big scoop. It's
42:03
Speaker 1: a big scoop of stuff. All right. Well, it sounds
42:06
Speaker 1: like a black hole is what most people think is
42:08
Speaker 1: at the center of our galaxy, But there are still
42:10
Speaker 1: a lot of questions about that, and there's even maybe
42:13
Speaker 1: a little bit of uncertainty whether it is a black hole.
42:15
Speaker 1: So what are we doing about it? How? How are
42:17
Speaker 1: we going to answer this question? Well, we have an
42:19
Speaker 1: awesome new telescope, this event horizon telescope, which is actually
42:23
Speaker 1: you know, like a collection of telescopes that all work
42:25
Speaker 1: together to make an effective telescope like the size of
42:28
Speaker 1: the Earth. And it recently took a picture of a
42:30
Speaker 1: black hole, right M A D seven, this black hole
42:32
Speaker 1: the center of a distant galaxy. And that was really
42:35
Speaker 1: cool because you could see essentially the size of the
42:37
Speaker 1: event horizon. You could see a black circle at the
42:40
Speaker 1: center surrounded by gas and dust that was emitting a
42:43
Speaker 1: lot of light, and that told you essentially the radius
42:46
Speaker 1: of the event horizon because you can see where the
42:48
Speaker 1: lights stopped. That's what's really awesome about that picture. So
42:51
Speaker 1: if you could train the same telescope at the center
42:54
Speaker 1: of our galaxy, you get a much better measurement of
42:57
Speaker 1: the radius of the event horizon if there isn't a
43:00
Speaker 1: black hole there, and then we could get a clear
43:02
Speaker 1: idea for what's really going on, because that's the thing
43:05
Speaker 1: we don't understand very well. It's like, what is the
43:07
Speaker 1: radius of this thing, whatever it is. Is it big
43:10
Speaker 1: and fluffy like a blob of dark matter or ice cream,
43:12
Speaker 1: or is it really compact less than a tenth of
43:15
Speaker 1: an au like a black hole would be. I see, yeah,
43:18
Speaker 1: I guess having a picture of another black hole at
43:21
Speaker 1: the center of another galaxy basically says like, hey, this
43:24
Speaker 1: is normal, Like, look, there are black holes at the
43:26
Speaker 1: center of galaxy, so probably ours has one to probably
43:29
Speaker 1: And this is challenging though, because it's very difficult to
43:33
Speaker 1: take these pictures, and it's harder in fact, to get
43:35
Speaker 1: the picture of the center of our galaxy than this
43:37
Speaker 1: other distant galaxy m A D seven. We could just
43:40
Speaker 1: sort of look at the center of it we're not
43:42
Speaker 1: buried in the galaxy having to look through most of it.
43:45
Speaker 1: We could look at it sort of from the side,
43:48
Speaker 1: from the top, you know, whereas our galaxy like we're
43:51
Speaker 1: right in the middle of it, so we have to
43:52
Speaker 1: look through all of this gas and dust to see
43:55
Speaker 1: the center of the galaxy. Right, And m AT seven
43:58
Speaker 1: also is targeted because it's like huge monster black holes,
44:02
Speaker 1: like really enormous. Where's the black hole the center of
44:04
Speaker 1: our galaxy? It's big, but it's sort of smaller on
44:07
Speaker 1: the scale of supermassive black holes. Right, Yeah, it is
44:11
Speaker 1: that I guess, closer than this other galaxy, but it's
44:14
Speaker 1: still you know, like fifty thousand light years away, right, Yeah,
44:17
Speaker 1: we're about twenty six thousand light years from the center
44:19
Speaker 1: of the galaxy, which seems like a lot, right, but
44:22
Speaker 1: astronomically speaking, it's really not that big. A number other
44:26
Speaker 1: galaxies are millions of light years away. Oh yeah, I
44:30
Speaker 1: guess it's just it's closer, but it's smaller and it's
44:33
Speaker 1: a dustier and it's also a dimmer black hole. Right,
44:36
Speaker 1: it's a dimmer black hole, and there's a more variability,
44:39
Speaker 1: Like the fact that it's smaller means that there's much
44:41
Speaker 1: more like variation in the brightness of this black hole,
44:44
Speaker 1: so it's not as easy to look at it to
44:46
Speaker 1: stitch this picture together. Now they've taken the data, like
44:49
Speaker 1: they turned the telescope towards the black hole effectively in
44:52
Speaker 1: two thousand and seventeen, and since then they've been crunching
44:55
Speaker 1: it through the computers to try to make this picture.
44:57
Speaker 1: So the only thing standing between us and a picture
45:00
Speaker 1: of the black hole the center of our galaxy is
45:02
Speaker 1: you know, enough computers, right, Yeah, we need more computers,
45:06
Speaker 1: but I think even if they we do get a picture,
45:08
Speaker 1: sometimes we're not sure if it's a black hole either, right,
45:10
Speaker 1: Like you were saying before, even the picture of the
45:13
Speaker 1: black hole we have in the other galaxy, it might
45:15
Speaker 1: not be a black hole, right, Yeah, there are other
45:17
Speaker 1: ideas for what could be that dense and that gravitationally powerful.
45:23
Speaker 1: You know. In the end, black hole observations are always
45:25
Speaker 1: a little bit indirect because you can't actually tell if
45:28
Speaker 1: there's an event horizon there or if it's just something
45:31
Speaker 1: that's not emitting and is very very dense. You know.
45:34
Speaker 1: It's sort of like we have a list of things
45:36
Speaker 1: that can do that, and black holes are the only
45:38
Speaker 1: thing on the list, So we assume that whenever we
45:41
Speaker 1: see something that dense, that gravitationally powerful, it must be
45:44
Speaker 1: a black hole. But then people come up with other
45:46
Speaker 1: ideas like dark stars, these very time dilated collapsing stars
45:51
Speaker 1: that could also do that. We don't know that's a
45:53
Speaker 1: thing in our universe or not. But in the end,
45:56
Speaker 1: until we go and visit the black hole, we won't
45:58
Speaker 1: know for sure if there really is an event horizon there. Yeah,
46:02
Speaker 1: so back your bags, Daniel, we're sending you all right.
46:05
Speaker 1: I'll bring my ice cream spoons. Yeah, make it a
46:08
Speaker 1: big scoop, all right. Well, it's a big mystery at
46:11
Speaker 1: the center of our galaxy, and it sounds like scientists are,
46:13
Speaker 1: you know, licking away at the data to get to
46:16
Speaker 1: the juicy candy center to find out the flavor of
46:19
Speaker 1: truth hopefully tastes like butter scotch or do legit. It
46:23
Speaker 1: tastes like hard work and a lot of GPUs. Let's
46:27
Speaker 1: be honest, it just tastes like coffee. That's what physics
46:30
Speaker 1: tastes like. Yeah, from all the coffee consumed to do it,
46:33
Speaker 1: chalkboard dust and coffee. That's the flavor of physics right there. Hey,
46:38
Speaker 1: you should come up with a candy for that and
46:39
Speaker 1: sell it chalk and coffee choffee. Yeah, it'll be good
46:42
Speaker 1: for your bones. Alright, Well, it's stay tuned. Well. We
46:45
Speaker 1: are slowly but surely looking closer at the center of
46:48
Speaker 1: our galaxy to find out what's at the center of
46:51
Speaker 1: it and what's inside could tell us a lot about
46:53
Speaker 1: how the galaxy got formed and even how the universe
46:56
Speaker 1: got structured and got to the shape it is today.
46:58
Speaker 1: And we're doing everything we can and to try to
47:00
Speaker 1: understand what's out there in the universe from this tiny
47:03
Speaker 1: little rock floating out in space. And every time we
47:06
Speaker 1: build a new kind of eyeball or figure out a
47:08
Speaker 1: new way to look out into the universe, we learned
47:10
Speaker 1: something new about what's out there. Yeah. I just hope
47:12
Speaker 1: we do it before it belt, but we hope you
47:15
Speaker 1: enjoyed that. Thanks for joining us, See you next night.
47:25
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained.
47:28
Speaker 1: The Universe is a production of I Heart Radio. For
47:31
Speaker 1: more podcast from my Heart Radio, visit the I heart
47:34
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47:37
Speaker 1: favorite shows. Ye