StarTalk Radio - Bug Splat Galaxies with Mordecai-Mark Mac Low

Episode Date: June 30, 2026

What type of planets orbit black holes? Neil deGrasse Tyson and comic co-host Negin Farsad sit down with Mordecai-Mark Mac Low to crack open the mysteries of galaxy collisions, dark matter, and the massive planetary systems around black holes.  NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free here:  https://startalkmedia.com/show/bug-splat-galaxies-with-mordecai-mark-mac-low/ Thanks to our Patrons Alex, Sadashiv Nayak, Raviteja K, Lian Zhalka, Thomas Davis, Alex Yumashev, Charles Koehl, Matthew Maldonado, Aleksandre Khatiskatsi, Grig Coker, Matthew Ardebili, Japeth Mitchell, Gaaary, Ian Patton, Casey Steelspine, Veninator, Hannu Latvakoski, Santiago Aguirre, Jonathan Caples, Ryan Wetmore, Dan Lepping, Chris, Frank Betz, William Massar, Jason Durden, Jenny Patton, LiveAlive42, Kesh Iyer, scott ezell, Jesse Jensen, Javier E. Gonzalez, rk89, Courteney Kawalek, James Martin, seth forever, Why So Serious, Jared Kennington, andrew bash, David Pillado, Jennie Hrobak, Mariana, Robbie Rogers, Michael Huckey, Anthony Torres, Luke Gilliam, David Hasenauer, Libby Higgins, Willie Lo, Mike B, and Rhagor for supporting us this week. Subscribe to SiriusXM Podcasts+ to listen to new episodes of StarTalk Radio ad-free and a whole week early.Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus. Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

Nagin, we learned all about colliding galaxies and the formation of planets. I had no idea how much banging and colliding and smashing there was in this universe. All the time. Coming right up on StarTalk. Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk. Neil de Grass Tyson.

here, you're a personal astrophysicist. This is going to be cosmic queries on the formation of planets in the universe. I got with me, my co-host, Nagin Fasad, McGin. Oh, my God, hello. Welcome back. I'm so excited. I have, I've, I've, like, peeped at some of these questions, and they are. Well, yeah, because they were already... Querylicious. Oh, querilicious. I love that. Very good. And just a reminder, you still have your fake Nation podcast. That's right. Every week.

Every week. And it's a delight anytime I hear you on, wait, wait, don't tell me. Thank you. That's the NPR, right? It's an NPR mainstay. An NPR mainstay, I've got a lot of tote bags to prove it. We have a good time. All right.

Let me introduce you to my guest today. He's a longtime friend and colleague, Mordecai, Mark McLo. Mortykeye. Well, hello, Neil. It's weird to... It's only been 30. seven years that we've known each other.

Yeah. So we, I mean, we came up together, you know, through graduate school, not at the same graduate school, but we're about the same generation. And it was, he's one of the earliest hires into our brand new department of astrophysics. Number one.

Oh, you were the number one high. I am number one. Into the department that you found. Is that a way of saying that he's better than you? No. Is that what I'm understanding? the department. Oh, got you.

I was his number one higher. Let's be clear here. You're just better than everyone else here. But Neil is still better than you. That's what one. There you go. Number one means he was hired first. Not that he's the number one guy.

We're all number one here. And what was a delight in your research profile is that you just need a powerful computer. And the universe succumbs to you. Well, it's a great. A good sandbox. Tell me what you do, because most people's stereotype of the astronomer, astrophysicist, we're at the telescope, or maybe we're crunching numbers on, not numbers, but we're on a theorist's not pad, and you are in the middle of that.

I'm a simulator. Simulator. So I do, I run computer programs that... That you write. Well, that I and my colleagues right. Yes. that describe how parts of the universe behave, using mathematical equations derived by theorists,

but using the computer to derive consequences that would be absolutely impossible to do with pencil and paper mathematics. So when things get hairy, we pull out a computer. Do you ever use your powers of simulation for, like, you know, a vision of a grill? cheese sandwich, or is it mostly just like space? Well, I would say that I may not do the grilled cheese sandwiches, but there is a simulator somewhere who does, I'm sure.

And they probably work for craft or someone. And they should be your next guest. There you go. So, Mornica, I remember when we were coming up, there was a catalog of galaxies, peculiar galaxies. In fact, it was called the Atlas of Peculiar Galaxies. Arp. Yeah, Halton. ARP, and we all scratched our heads

wondering, how would nature make objects that look like this? Like bug splats. Yeah. The galaxies are just, what? What? And I think in our lifetime, bringing computers to bear

on that problem, we would fully understand how you get a disturbed-looking galaxy. So that's actually an interesting story, because the very first simulation that was done of colliding galaxies that made a bug splat and reproduced these peculiar observations was done in the 1940s using lamps and photo detectors and as an analog computer because the

lamps simulated gravity because light drops off in intensity just like gravity does and that actually revealed the basic picture that you get these splats, these tidal tails, we call them. But then we came along and refined that insight with computers. Yes. But the first one was those photo detectors. Interesting. That wouldn't be Holmberg, wasn't it? I think it was.

You're right. I remember that. Yes. Yeah. So. You've written about this. But I was just a triumph of the simulation modeling universe. Absolutely.

Where, so there's a famous astronomer in the day, he would say, a Lexus that's wrecked in an accident is not a different kind of Lexus. It's just a wrecked Lexus. And so a wrecked galaxy could have been a perfectly nice galaxy, but then it collided with another galaxy. And with your computer, you can check what it looks like at every step. That's correct. And then look at it.

the universe and find... Those steps. All of those steps being taken by colliding galaxies. And that's how we learned that bug splats turn into beautiful elliptical galaxies, smooth, uniform, homogenous, because they get complete... They're disc galaxies that get completely blenderized. And that's the origin of the elliptical galaxies. Furthermore, every galaxy in the universe has...

collided with other galaxies. That's how galaxies are made. Wait, so is it that like when two galaxies collide? Is it sort of like... Say it more romantic. When two galaxies collide. When two galaxies collide.

Come together. But when that happens, is it that like they're at a stop sign and neither of them is willing to go so then they just smash into each other? Well, it's like this. Galaxies are made of stars and gas and dark matter.

And stars are very widely separated from each other. So the stars just go by each other. Maybe they tug each other a little gravitationally, but basically they're not going to run into each other. If there were four bumblebees in the continental United States flying randomly, there's a greater chance that two of them will accidentally bump into each other than two stars will collide in the galaxies. That's about right.

hearing there's a lot of space. Yes. Is that what we're doing? Okay. Got it. Got it. Okay. However, gas is space filling.

And so the gas runs into each other and lights up, huge shockwaves, dust clouds running into each other, new stars forming. All that goes on during the collision. I got a good analogy for colliding gas clouds. Two hot marshmallows. When they hit, they're stuck. Have you done this? No. You look at me like, what is he talking about?

I mean, have you done this? Have you, like, roasted marshmallows and then, like, throw them at each other? Like, I have it, Neil, I don't know what kind of coffee trips you went on. We ate the marshmallows. He's looking at us like we're the weird ones. I don't know. But I like this. So they don't, they stick together and then that's it.

They become one marshmallow. Got it. And there's an edge between them and everything. So I'm bringing this up just as. But they don't even at x-rays. No, they don't. last I checked. So I'm bringing this up just as a triumph of the

numerical simulations to understanding the universe. And you've made a career of doing just that. One of the, another great mysteries that we had to figure out was weird galaxies that had weird things going on in their centers. And they give off a lot of energy and a lot of different wavelengths. And we came up with the unpoetic name,

active galactic nuclei. Or quasars. for the brightest ones. Especially of late, this has been a big part of your objects of affection. It's one strand of my research, yes. Oh, just one strand. Just one strand. Yeah.

And so tell me about AGMs. What's the latest on them? Do they all have black holes? They all have black holes. That's what makes them so bright, because black holes are the brightest objects in the universe. This is where you come in and say, how could a black hole be bright?

Yeah. How could a black hole? be bright. I don't understand. Thank you for asking. And is there a way for the black hole in my soul to brighten up as well? Yes, yes there is. Eat a lot.

Because that's how black holes get bright. So you have gas, and we have already established that if you squeeze gas enough, it gets really, really hot. And if it's really, really hot, it emits a lot of radiation as the fourth power of the temperature. And so what is better at squeezing things than an almost extremely tiny, extremely massive object, like a black hole?

So you have a black hole in gas, and particularly in the centers of galaxies, there's a lot of gas because it all gets swept into the center as you wish the vacuum cleaner would do. But anyway, so here it is, all this gas falling onto the black hole, and there's not room for all that gas to fill.

and so gets squeezed and squeezed and squeezed until it reaches a billion degrees. Fahrenheit. And... I was going to clarify. Yeah, no, thank God. Okay. You were wondering that too, right?

Yeah, of course. So when it's that hot, it's emitting in the x-rays, and the ultraviolet, and all that light is coming out. And that, a lot of it gets converted down into the visible by running into dust clouds and stuff. And just to back up on that, if you have an electric stove, when it's off, it just is off.

It's emitting in the infrared. Yeah. Just mildly. But then you turn it up a little higher. And then it feels warm, it's emitting more infrared, and then it becomes visible. But deep red.

Yeah, it's emitting visible light, but also still emitting all the more infrared than before. But it kind of stops there. But if you keep cranking it up, it'll get orange hot. Orange hot. Wait, so you could have like a black hole in your kitchen?

Well, we're getting there. Not a good idea. X-ray emission is unhealthy for human beings. Oh, got it. So you keep turning it up if you could. It would then glow white hot, then blue hot. Like a welding torch. Right, but then that's all you can see.

But it'll keep what's beyond violet? Ultra. Ultraviolet, ultraviolet. Ultraviolet. Yeah, that's gold, cool, cool. Yeah, how about it? And now you're getting your sunburns. Yeah.

And so at a billion degrees, you are warm. You're way deep into the X and gamma, right? X-rays and gamma rays. So you don't want to be too close to one of these. Okay, so hence the word active and active galactic nuclei. So these objects are literally the brightest objects in the universe, and so we can see them across the universe out to, you know, 95% of the distance to the back,

when you're looking across the universe, you're looking back in time, so 95% of the distance back to the Big Bang. Big Bang, we can see these things. Show-offs. Totally. They're show-offs of the milk galaxy. Of the universe. Of the universe.

The Milky Way does have a very massive, super-massive black hole in its center, but it doesn't get a lot to eat. So it's kind of a wimpy, dim little thing. But back then, were we ever a quasar? There is actually evidence that quite recently, like just five million years or so, ago, there was a much brighter outburst from our own galactic black hole. And there's now a shockwave, like running out of the galaxy. That's how you trace it, I guess. Yeah. Yeah. It was first discovered using the Fermi gamma-ray satellite. Yeah, but do, is our black hole big,

do we have black hole envy here? Oh, yes. We only have a million solar masses. The biggest quasars can be a billion solar masses, a thousand times bigger. Yeah, it's embarrassing because like once you go big black hole, really don't go back, and that's like something that every astrophysicist says. That's right. Black holes do not give up mass easily. Putting them on a diet takes a very, very, very long time. Wait, can you tell me the size of these black holes in like the B, the B, like continental United States analogy? Yes. Oh, yeah, sure, sure. So a billion solar mass black hole is a little smaller than the solar system. A stellar mass black hole, like one solar mass, is, I want to say, a kilometer or so?

Yeah, I think that's right. Yeah. A mile. Got it. It's not as big as Central Park. Okay. Yeah, and if Earth were a black hole, which would never be, but if it were, it would be the size of a plumb.

A marble. Oh, got you. Yeah. So compressed. Yeah, yeah, so compressed. But while the solar system is big, that's tiny compared to the whole galaxy, and gas clouds are way bigger than that. Oh.

So much bigger. When you talk about funneling them down to something as small as the size of our solar system. I mean, your average gas cloud is, let's say, a million times as big as the distance from the Earth to the sun. Space is big, big. Yeah, space is like angeringly huge. Well, some people could think that they'd like their space. Why do UFO sightings persist? Are at least some of them figments of our imagination?

or are we missing something? In my latest book, Take Me to Your Leader, I separate science from speculation. I actually explore what's possible in this universe, given the universal laws of physics. Because if the aliens are out there, the laws of physics will dictate how they find us.

I also narrated the audiobook. So I'm duly informed that the audiobook and the print version are available now, wherever books are sold. You have not stopped there, of course. You have explored the formation of planets in these environments. So I started out by working on the formation of planets around normal, boring stars. And I went so far as to...

Is that what we all care about? Well, I would think so, but you're bringing up weird planets. Okay, right. Okay. So I started out just thinking about the thing we care about, how did the Earth form? And I went so far as to hire a postdoc, Vladimir Lyra, to study this with me. And we were going along, perfectly happy, studying planets moving around in the proto-solar disk. And he made the mistake, or maybe the very wise decision, to talk to some of our city university, CUNY colleagues,

who were doing research here on AGNs. Oh, okay. Okay. On the disks. have here in our department, we have many frequent visitors from nearby universities with resident interests. In particular, we have an NSF-funded partnership with CUNY. What's official? NSF official. NSF official. To bring students and faculty from campuses across the city to do research here at the Research Intensive American Museum of Natural History.

Is that what pays for the pizza every Thursday? There's like seven boxes of pizza come in. People only think when we're eating. What's the favorite topping of the astrophysicist community? Is there like a way? I believe we ensure that all diets have an option. Okay, yeah. Okay, but back to AGNs, which are kind of like pizzas

because they have discs, very flat distributions of gas and dust around them. Because stuff falling onto an object, if that stuff can cool off, like gas can radiate and cool off, it will form not a ball around it, but a flat disc. Same thing happened in our solar system. That's why all the planets. It's a rotating disk, not like a pizza. But like a pizza being made. Or like a sushi conveyor belt. Let's stick with the pizza being made.

I hate those because that means the sushi went in front of the nose. people. You have other people. I don't tell about that. Big Japanese scandal. So you've got this flat disk, and there's stuff accumulating in the disk. It gets dirty and dusty. And that dust starts to stick together.

And, well, if you're in a normal disk around a normal star like the sun, which isn't quite normal, it's bigger than average, there it makes planets, like, say, this one that I can observe under my feet. However, if you're in a disc around a supermassive black hole, a hundred million times as massive as the sun, there's an awful lot of dust in that disk, and it's awful large. And you don't form three planets or eight planets. You form a million planets. So you made a million planet star system.

Planetary system. Planetary system. Planetary system. around the black hole. And this was a paper that we just had accepted a couple, like two weeks ago. Oh, God, breaking news. Yep. Okay.

Although I will say, so Bupendra Meshra was the lead author on that. How many authors are there? Let's see. I think there are six. So this is typical when you have collaborations. Absolutely. And some of them are CUNY professors as well. CUNY, Barry McCurnan.

CUNY City University of New York. Yeah. Barry McCurnin and Savick Ford. Vladimir Lyra, who was a post hoc. Savick Ford is named for a character on Star Trek. Well, she named herself for it. Oh. I was going to say, wow, her parents really figured that out. No, no. Her parents know, she did.

But I think it's official. I mean, I think it's... Oh, yeah. She publishes under that. She's committed. Okay. K.E. Savick, board. Yes. Yes. Okay. Anyway, we showed that if you take standard planet formation theory, and this is the same trick that Blod, Barion, Savick did

15 years ago to realize that black holes could move around like planets, if you take standard planet formation theory and apply it to the dust, you find that it is very liable to go through all the stages that you would go through to make planets, except they're really big planets because there's so much dust. So how big a solid planet? Jupiter mass, solid rock planets, except they're probably not rock, because they're probably degenerate in the centers.

Wait, wait. So our Jupiter is big, but it's mostly gas. It's mostly gas. You say you can make a Jupiter-sized planet that's walking. Out of silicates. Ooh. Ouch. So, yeah.

Does that mean also that it's gravity is like extra annoying? Yes. Got it. Because it's so. Extra annoying being like strong. Yes. Yeah, we followed that. We totally understood you in the game.

Totally. You're so good. I just need to like translate for this. In fact, you are absolutely right. Because the gravity at the cloud tops of Jupiter, we won't call it the surface. but at the cloud tops of Jupiter is quite reasonable. It's not far off from Earth's gravity. It's like 10 times gravity?

No, no, no, no. Not even? Not even. It's close to Earth's gravity, because Jupiter's so big and low density. But the gravity at the surface of one of these monsters would perhaps be 10 times Earth's gravity. I don't know.

I haven't done the calculation. It's an easy calculation. But you're the same density and, you know, 10 times the radius. We don't expect to find life on any of these because there's no home star to give nourishing energy to play life. No, it's rather worse.

There's a home center of the accretion disc glowing in x-rays and gamma rays. It will provide plenty of energy, but it might not be in a form conducive to life as we know it. It's hostile to biology. That would be my suspicion.

Is there a biology that we don't know of that could maybe handle it? That is an excellent question that we don't know the answer to. No, no, there is. The Hulk biology. Right, right. The Gamerae biology.

Can you add the Hulk into your simulator and see what happens? We're going to have to get his specifications. Yeah, yeah. I want to see this. So if all you need is dust, which are the larger molecules, a larger gathering of atoms. Minerals. Okay.

These are silicates. He says dust like, kind of like we find on the Earth, except it formed in space. even though space is, as noted, very large, the rocky atoms of silicon and oxygen and magnesium tend to find each other, and once they find each other, they stick together. And so they form little tiny dust grains, like a nanometer in size and deep space. But when you collect all of them together, whether it be in a protostellar disk or a supermassive black hole disk, they can find each other and stick together.

And actually, that's something else I've been working on recently, is showing that they might be a lot stickier than people have thought. So when they stick together, they stay. They appear to stay. Well, until they get big enough, and then they break apart when they slam into each other. And that's actually a big question. That's a big question in planet formation theory is,

how do you get them to stop beating each other up and fragmenting? Yeah, because is it also, I mean, partially what you're describing almost sounds like a sandcastle, like they're sort of sticking together like a sandcastle. That is an excellent. a description of an asteroid. We call them rubble piles, but it's really a sandcastle. But so that it's so they're pretty vulnerable.

They're totally fragile. How did we learn this? Back, oh, 30 years ago, a comet swung too close to Jupiter, comet shoemaker Levy 9. You're supposed to not just make faces. This is a, first ever observation of a comet slamming into one of our own planets. Yes. Yes. Or do you memorize all of the comments?

No. Just the famous ones. Just the popular ones. Because I was very impressed if you had them all down. No, no, no, no, no. There are thousands and thousands of. I'm no longer impressed. Go ahead.

Very good. Back as you were. And I have to just put in here that duo. By the way, the Shoemaker Levy nine, okay? It's really Shoemaker's Shoemaker Levy. Was there eight others? They're active bunch. Oh, yeah.

And that collaboration had a leftover asteroid that they named in my honor. Yes. Okay, I knew you had an asteroid. I didn't know it was the shoemaker-leafers. It was a shoemaker-leaf. And the plaque is right up there on the... Sorry, quick question. Who decides these things?

Is it you? The discoverer, but it has to be approved. Okay, yeah, yeah, yeah. You can't be rude. So it was that duo. That's how... Trio. Trio. That's how fertile a discovery group that Gene Schumaker, Carolyn Schumaker, and David Levy. They've discovered comets and asteroids and all the kind of things.

And Gene Schuemaker also pretty much was the originator of the theory of craters. Like what happens when something, a big rock slams into a planet? It makes a crater. He described how. And so that's... It sounds obvious. I know. I was just going to say, like, I can also ask my... seven-year-old daughter about the theory of craters. I think she'd come up with the same thing. That's how fundamental his work was.

Because before Gene Shoemaker, people looked at the moon and saw volcano craters. Right. Not. Not okay. Every crater was a volcanic caldera. Yes. But they're not completely crazy to think so.

Well, Crater Lake is a volcanic caldera. Right. They're not crazy to think so. They were just wrong. It's possible to be, that makes complete sense, you're just wrong, okay? That happens in science all the time. It's very frustrating. But the reason is the argument against them being asteroids was every crater is a perfect circle on the moon.

And no one is thinking asteroids are coming straight in. Surely some are coming at an angle. And if you're coming on an angle, you'd expect an oval. Right. Most of them should be ovals, but everyone was a perfect circle. And so that's the tension between the two arguments and the two camps. And it wasn't until we had like, we can model. Well, until Gene Shoemaker came along and said, no, they should be circles.

No, no, someone had to demonstrate with a computer simulation that a high-speed impact, when it hits, it explodes. It vaporizes. And that explosion makes a perfect circle, even if it comes in at an age. Okay, but we're off the topic, which is that when Cometheus you make or Levy 9 passed close to Jupiter, it felt gravitational forces from Jupiter, but it was coming by at a fair distance and those gravitational forces were not strong, massive planet gravitational forces. They were forces equivalent to one-eighth of an inch of water in Earth's gravity.

How much pressure does that put on your plate? Not much. That's all the force. That tore that comet apart into 21 pieces. That's how weakly bound it was. Right, because your sandcastle is exactly right. Oh, I feel so smart right now. It's so validated. Yes, I love this moment.

You're welcome. Yeah, and so just to show there's still a huge frontier for us to understand these objects. Yeah. And you got people, good people working on it. Including the guy that said, when a thing hits another thing, forms a crater. Yes. Yes.

Which like, I can't believe somebody. Somebody had to do it first. Yeah. So we got questions from our audience who've been specifically clued to your research profile. Okay. And the questions will emanate from that. So what do you have here for us, Nagu. I haven't seen the question.

You haven't seen them either. I have not seen them. And I've seen them. I think they're great. Here we go. Tatiana here from Ottawa, Ontario. I'm 15 years old. and finally asking my first StarTalk question.

Oh, right. Congratulations. My question is, what are and how do supersonic, turbulent flows and magnetic fields regulate star formation inside molecular clouds? How many hours do I get? She's not done. Do they work together to stabilize the process? Or does their interaction create chaos? Yes, yes, and yes.

Yeah, it naively feels like that would just mess up the whole thing. You're getting coherent planets out of this, aren't you? Stars. Stars. Okay. Okay. Yes, the turbulence stirs things up, and it also squeezes some of the gas. And so the squeezed gas, gravity can take hold and start the collapse process.

But the stirring prevents more gas from getting grabbed by gravity and collapsed down to form stars. So it's both, both and. The stirring actually wins. So the more turbulence you have, the less star formation you have. Okay, but when you have a little pocket that's slightly more dense, that attracts more material that makes it even more dense. And so it's a runaway. It's a runaway.

Once you get started properly. Once you get out of the starting gates. Yes. Okay. Now, then what happens is that as you start forming stars, the biggest, most massive of them, pump huge amounts of energy back into the gas. whether it be through jets or ionizing radiation or stellar winds or ultimately supernova explosions and that chases the gas away and then you don't get any more star formation. Okay, now how do you know all this?

Because I've done simulations of it and then I compared those simulations to what observers saw and they weren't so bad. So if you didn't have observations to compare it to, you're just kind of presuming your results are real. I'm playing in the sandbox without any constraints. And then I can make... More sandbox analogy here. I mean, we can't stop with it here. Do you have, but you feel, like, so how much, like, what level of confidence percentage-wise is it?

Okay, so, okay, so the point about constraints is important because otherwise someone else can come along and say, no, no, no, no, no. The magnetic fields are going to hold everything up, and you're going to have to wait. for the neutral atoms to drift through the ions to ever, ever make a star. Without observations, we can't tell who's right. Because he can say, of course, it works like this. I've written 20 papers on it. And I can say, but my programs don't show that.

But, well, you know, so I wrote my programs wrong. One possible, you just went too quickly past that. I'm sorry. What you just said was that your naysayer could be right. And maybe you, your software had put bugs in it. No, approximations. Approximations. Okay.

We always, every model has approximations. We don't know until. Until you compare to the observations. There you go. Okay. And then you get a reasonable level of confidence. Then you build up your confidence. And of course, then you argue about what the observations mean and whether there was noise in the telescope.

And, you know, what assumptions went into the end. interpretation of the observations, but ultimately this is how science progresses. You come up with an idea and then you have to, then other people come up with different ideas, you argue about it, and you settle it by reference to the real world.

A duel. Oh, not a duel. Okay, sorry. We try to avoid that and most of the time we succeed. Somebody shot a minute at butts. But it's evidence that arriving at what is objectively true in the

actual universe is messy. Totally. So messy. So messy. And the strength with which you argue your point ultimately is not the arbiter. No, unfortunately. It might be easier that way. And it doesn't matter how articulate you are or how charismatic you are.

We have the ultimate. Facts still have to win. Judge, jury and executioner is nature. That is the agreement the people doing science have made with each other. It's an implicit agreement. One hopes it's explicit. but is that we will settle our arguments ultimately by reference to reproducible experiments and observations. Yes.

So either I'm right and you're wrong, you're right and I'm wrong, or we're both wrong. It'll be decided by more data or better data. That's right. Yeah, okay. And that is the central tenet of science. Where does the magnetic field come from? The magnetic field comes from a dynamite. So dynamos happen when you get some sort of stirring of charged gas or charged things.

Oh, okay. So like a dynamo in a power station, the charge is running through wires. And it's spinning. And it's spinning. Yes, yes. And in the universe, or in the earth, the dynamo is turbulent, swirling magma, deep down in the earth. that is kept molten by the pressure and radioactivity of the earth. And it swirls around and makes the Earth's magnetic field, and that's a dynamo.

Well, same in the sun, except there it's plasma. In galaxies, the charged gas between the stars forms a dynamo, stirred by supernova explosions and by gravity. So if you didn't have the turbulence, you wouldn't get the dynamo. You wouldn't have a magnetic field. You would not have a magnetic field. in hand. One generates the other.

Okay. It's like they're in heat and then they give birth to this. Sure, maybe. I think you're stretching the field here. But if you stretch the field and twist it and rotate, you will get a dynamo. Great. Thank you. Okay.

So the first dynamos happen when the very, very first stars form. And ever since then, we've had significant, magnetic fields running around, getting stretched and twisted and folded to make more magnetic fields. There we are. There we are. Should we move on to the next question?

Next question. Thank you for that. All right. Ismail Veldels here asking my first question from a vineyard del Mar, Chile. Okay. In regards to stars and gas giants, if Jupiter was sufficiently massive,

would the pressure ignite, would its pressure ignite its lighter components? Yes. Furthermore, do the sun or stars in general share elements with gas giants like a rocky core, or is it fused gas all the way through, which sounds like a tough meal at Taco Bell? I don't know. Go ahead. Let me modify that just a little bit. If we had the capacity to dump mass onto Jupiter, could we ignite it one day?

Yes. He had two questions. First question is if you increase Jupiter's mass doesn't ignite. And the answer is yes. If you increase Jupiter's mass enough, like, well, if you get it up to about, I want to say, 10 times the mass of Jupiter, you get the deuterium burning, the heavy hydrogen with extra neutrons. And that lasts for a little while, but there's not a whole lot of deuterium in the universe. It's like, I don't know, a few parts in 100,000. So you get a little flash of light for a couple of maybe a million, a couple hundred thousand years and then it's gone.

And that's a brown dwarf. And they exist. And we've got one of the world's premier research groups on the topic right upstairs here. Run by Jackie Farrity. Because we just went down the hall to get Mordecai. Yeah, yeah, yep, I traveled a long way. I want my per diem. In the Department of Astrophysics of the American Museum of Natural History.

That's a brown dwarf. Now, if you keep piling mass on and get up to, bu, blah, blah, blah, blah, in Jupiter masses, like 80 times. Oh, that meant that much. Yeah, 80 times the mass of Jupiter. That's a lot. Which is a little under a tenth of the mass of the sun. You could just drop Saturn onto it.

No, that would be amazing to watch. But not nearly enough. That still wouldn't ignite it. No, no, no, not even close. Not even close. Not even close. Well, so you, as you said earlier, like something like that is just like a couple hundred thousand years. It's like dumb.

That's what, that's the brown dwarf. Don't call brown dwarf's dumb around here. Okay, no, I'm just trying to understand because you made that sound like not nothing. Like it was, okay. It's fusion, but it's not a lot of fusion. Okay. But if you get up to say, wait, wait, wait, wait, wait, that's a. It's a flash in the pan.

Gotcha. Okay. But if you get up to 80 times, then you can ignite hydrogen. and there's a lot more hydrogen. That's what Jupiter is mostly made of. Then you've got a very low-mass star. And very low-mass stars sit there and simmer for longer than the current lifetime of the universe.

So that will keep going and going and going. So that's way more than 200,000. It's way more than the life of the universe. It's like 10 times the life of the universe. No, 100 times the current life of the universe. Yeah. But question, right now Jupiter has a rocky core. Yes.

happens to that rocky core because it's kind of related to this question. Absolutely. Yes. Yes. Deep down in there. Let's go. Let's go. Let's go.

Bring it on. Okay. So what happens is it gets completely overwhelmed by all the hydrogen and just gets mixed in because the hydrogen is sitting there fusing. So you have a little tiny rocky core. Now the sun, of course. Why doesn't it just vaporize the rocky core? Yeah.

That's what I'm saying. Okay. It's not rocky anymore. But it is the elements of the former, the rock, a core formerly known as rocky. are now part of the fusing vaporized hydrogen in the center of the object because it's now far hotter than anything, any rock has any right to withstand.

So it's vaporized all the rock. That's right. Now remember, the sun also has silicon and magnesium and aluminum and oxygen in it. It's just all mixed in with the hydrogen. Right. So, yeah, the sun, you might think it would have a rocky core the way Jupiter did, but for that same reason,

it's all... It's too hot. It can't be anything other than loose atoms and electrons even. It can't even be atoms, except on the very, very surface. And atom is a nucleus plus electrons. Yes. All the electrons are gone. Yes.

In the center, they're all gone. They're just roaming freely away from their parent atoms. Got it. Here's your cue. Yeah. Like, they're having a rebellious phase. Oh, they are long gone. Never to return.

Never to return. They're not just like T-Ping their geometry T-T-E. house or something. No, no, no. Okay. T-Peeing. That's a thread. Toilet papering.

Yes. Have you done that? I have. No, not. No. I teepied once in my life. Oh, in your day. This is a story you tell.

Back in the day. Tell your offspring. I'm afraid we didn't do that in the center of New York City because a six-story apartment building is hard to pee. You're just like doing, you're just doing toilet paper on someone's door. And it's a lot less, you know. Satisfying. Yeah.

Can't imagine. I'm Nicholas Costella and I'm a proud supporter of StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson. Time for a few more questions. What do you have? Okay, let's see. Hello. How is dark matter incorporated into your simulations, random distribution or what?

Okay. Sorry, and this question is from Ben Grund. Great question. And the answer is any which way I can. So sometimes we actually put in particles in the simulation and watch them roam around under the force of gravity. And, well, they're very massive particles, but they still behave like dark matter

because they don't interact with the gas, except by gravity. Other times... Well, you just said, since we don't actually know what dark matter is... Oh, no, no, no. We're not even going there. No, but you know it has gravity. Yes. Your simulation has to get it somehow.

So you sprinkle in, you invent a particle that interacts only by gravity and has enough mass. Enough gravity to match the observed dark matter. The observed dark matter. Okay. Yes. So this is by, as they say, by Fiat, you do this. Does that the right?

No. I mean, you could say. If I understood what any of these things were, I could weigh in on if you used Fiat correctly. I wouldn't say it's by Fiat in the sense that, you could say. The whole simulation, by that definition, is by Fiat. Okay. Right? I've added in a field of gas.

I've added in star particles. Okay. So it's just one element with the simulation. So it's a way to get a source of gravity without having to worry about it after that? It behaves like dark matter. The simpler way to do this, which I also sometimes do if I can get away with it, is to simply put in a gravitational field that reproduces the dark matter distribution and then let that handle it without having to actually do. track particles

without having to track particles and pay attention and do accounting and get bugs and all the rest. All right, so is it smoothly? It's a smooth feel. It's not...

It's smooth if you're on a sub-galactic scale, but if you're on a, you know, galaxy forming scale, it's very, very clumpy because the clumps are the galaxies. So in that sense, when I'm simulated,

in formation of the first galaxies, then we're seeing big clumps of dark matter that the gas falls into and then you've got a galaxy. So I've heard this, I think it's right, that dark matter, whatever it is, is so prevalent that when you just, when we look at and describe stars and galaxies, this is the froth on an ocean.

Well, one sixth of the mass of the galaxy is in anything visible, stars, planets, gas, comets, all of that. One sixth of the mass. So 85% of the gravity is from dark matter. It's something you only know what it is. We know it exerts gravity and we know it doesn't move at light speed. That's why it's cold dark matter.

But is there like an area like that doesn't have any, like how Wyoming doesn't have people? Like is there an area of the galaxy or like there's no dark matter? Like Wyoming doesn't have people. Voids don't have dark matter. while clusters have lots of dark matter. Okay. And filaments have, well, intermediate amounts of dark matter. They're like interstates.

Okay. People cluster around the... So it's not so evenly distributed. It's absolutely not even. Not in the universe. Not in the universe. Right. That's why we call it the cosmic web,

because it looks like spider webs, like with thin filaments and then big spaces in between. Right. So we'd say web now, but I remember a cross-section of a sponge. Does a sponge still work as a... Sponsch still works. And sort of areas around it and places where you intersect.

These days we usually talk about webs. Webs. Okay, that's fine. Ditch the sponge. I was kind of into sponges, though. I mean, I know. You really got into it. Well, that was an analogy for the interstellar medium, too.

Yeah. You know, Chris McKee and Don Cox arguing about, is it a sponge or is it little round clouds? I had a cameo and SpongeBob. I was Neil DeBass Tyson. Oh. Astrophysicist. So I just thought, I'm sticking a sponge. You got it.

Okay, thank you. You can have the dark, the cosmological sponge. Yes, thank you. Thank you. Time for a couple more. Okay, let's see. We're on a roll here. Yes, we are.

So Gavin Bambor from North Vancouver, please visit, they add. How long does it take to form a star or a planet? Is it the same process we're both and the same stuff? Ooh. Okay. I believe the answer is yes. And yes. And so how long does it take to form a star?

The main formation phase, when most of the stuff comes down, is maybe 100,000 years. But it trickles along. That quickly, even. 100,000 years. Yeah, that's like the main accretion phase. But it's going to trickle along with a disc and accreting more mass and forming planets for a couple of million years. So you'll form a star. before you form the planets?

Well, that's an ongoing controversy. That was the idea, that used to be the idea. Wouldn't that be the case, right? You would think. But nowadays, the more we examine the question, the faster the planets seem to form. And so now I would actually say that the first planets formed during that main accretion phase,

very, very fast. But then you continue to form planets and planetary-like things for several million years. years. And once again, you get meteorites in a disk. In a disk. It's all dust and gas in a disk. I have an accretion disk right here.

Yeah, yeah. If you want to get brighter, eat more. Okay. Like the Quasar. That takes so long. It's just like everyone has to be really committed to that planet for it to form. You know what I mean? Because it takes a few million years.

Oh my gosh. On the other hand, where are you going to go? You're stuck in this disk going round and round and round and round. Let's get it going. Eventually, we'll have an ongoing. Arby's here or whatever. Yeah. Well, the development of Arbyes

takes a lot longer. That's billions of years. Observably. As Carl Sagan said, how do you make an apple pie? Start with a big bang. Right. Yeah.

Go find the chicken. Time for another question? Yeah, let's do it. After all the model runs, how often do planets form with a satellite as large by percentage of mass of the planet as our moon.

Good one. That's a very good one. And the answer is that the computer simulations aren't high enough resolution to really get a good answer to that yet. And so that is a current research question. But you can't see the moon? But we have all these planets with wimpy moons. Yes.

Right? Yes. So we already know. Well, observationally, we know in one planetary system with, one set of initial conditions that moons like the Earth are pretty rare. And that's all we know. How many planetary systems do we know of? Well, it's growing now.

6,000 are counting. It's growing. It's growing fast and it's going to keep growing. And we don't know if any of those planets have moons because, observationally, we haven't been able to see them because it's really hard to see a moon around a planet. It's already really, really hard to see a planet, much less a moon. And David Kipping up at Columbia thinks he's found a moon, but everybody else is staying on the fence and saying maybe it's...

David Kipping, we've had him on StarTalk. I'm sure you have. She's got a lab, the cool world lab. Yes, which is kind of cool. And he's got a podcast. Yes. Which funds that lab. Cool world.

So, wait, your simulations will sometimes see like a hint of a moon? My, well, I don't do those simulations. Okay, but our simulations, the fields, you can make moons, and we know, I mean, we certainly know how to make the Earth's moon, slam a Mars-sized planet into a Proto Earth, and that works shockingly well, as evidenced by the Apollo astronauts bringing back rocks that had the same composition as the Earth, because they formed from that super collision. Because they never went to the Moon to begin with.

They left from the Earth to the Moon. We'll cut that out in that. We'll edit that out. But that meant that the moon didn't form organically with the Earth. It formed afterwards. Afterwards. But now what the Earth is made of, of course, is also a mixture of Proto Earth and I think they call it Ares, the Mars-sized that I'll object.

It's... Thaya? Thea. Isn't Thea the Proto Earth and Ares the Proto Moon? Oh. I mean, the... I think Thea is the Proto-O-Moon. slamer. Confirming now,

via NASA, that the ancient proto-planet that we collided with was Theo. Okay. So shockingly successful as this model that we even named the object that doesn't exist anymore. That's right. The impact object. Which is obliterated. Yes. And became part of the... We gave it a name.

Yes. However. However, we got a cool name. We can do those sorts of calculations for planets elsewhere, but to get the frequencies, that means a lot of calculation. We don't have enough computers to do that currently. Well, I love me my moon because our moon is the same size on the sky as the sun. So we get beautiful eclipses.

Oh, I love it. Nobody else has eclipses like that. At Jupiter, it's got moons, but the sun is far, the moons are small. Nothing matches up the way our moon and our sun. So what is it? The moon is 400 times closer. and one four hundredth the size. Yep.

So everything ratios exactly. Exactly to the, yeah. Yeah, it works out. And that's how you get eclipse chasers. Yeah. It's the greatest spectacle of nature, a total solar eclipse. Second only to Manhattan Henge,

which is also something because... You got you some Manhattan, Edg. I love a Manhattan Hens. Oh, my gosh. Thank you. That's because of you. Yeah, I followed your dates. Oh, okay.

So Mordecai, time for one more question. Okay. We've been going. It better be a good one. And you're a good question-answerer. You've been succinct and efficient. Okay, I will ramble. No, no.

Let the question on us. Okay, here we go. From Emil Rougeau, who describes himself as a man who has forgotten what curiosity is. As once said before by you, Dr. McLough, eight to ten years ago, quote, we live in a time where we have understood that the universe is far stranger than we would have thought. Have these thoughts changed over the years? or have they made more problems for you? I would have to say that if anything, these thoughts have intensified.

The universe is far stranger than we once thought and far stranger possibly than we can imagine. Why do I say that? Because we live in a universe that is expanding, that is accelerating, that is forming stars, planets, black holes. And it all came from a almost perfectly smooth, homogenous, hot, very, very hot beginning.

That's not a story that someone 100 years ago would have told. None of it. So, yeah, strange. I have books, old books, that describe the universe as an ordered, majestic place. everything in the right spot, everything in in stately orbits around you. And then we found out that things slam into each other.

They blow up. It's full of turbulence and chaos. Yeah, I mean, it's just a mess. Yes. Thank you for that cogent description of the modern understanding of the universe. Wait, so can I ask you both a question then? Now, you're both in the field of trying

to understand the universe better, right? Okay. solving mysteries. Are we all at some level trying to understand the universe better? I guess if like doing a tight 10 at the chuckle Hutton-Shiboigan makes solves the universe in any way, I might be in that business. But does it make either of you feel, I don't know, bad that like the more you study, the like more you find it chaotic?

I don't mean, I don't know. Let's just say it keeps me in a job. I have a different way to answer that. Yeah. If the universe were more and more chaotic, requiring equally as complex laws of physics to understand it, then what are we doing? But the real majesty is that it's just a few laws of physics. That generate all that chaos in mass. That generate all that chaos.

It's just a few laws of particle. physics that account for all the particle zoo that we know and love. Except for dark matter. Except for dark matter. We're not there yet. So we're working on it. If to understand the universe required a complexity of theorizing that matched it, then all bets are off. I'll just go home.

You know, go to the Bahamas, give up on it. But if foundational understanding, like Mordecai, you said all this without even mentioning that you're an expert in fluid dynamics. I implied it by discussing the turbulent dynamo, which is absolutely an extreme fluid dynamics problem. Yes, but fluid dynamics. Magnetized fluid dynamics even. Look, he made a face.

He was like, I'm angry. So fluid dynamics is the study of fluids, which can be gaseous or liquid. Kitchen sink. There's a whole set of rules just for fluid. dynamics that works in water flowing through pipes as it does in stars in stars so that is the that is the majesty of the universe right because you're you're you're settled on some on the rules and now you're just like watching to see how these rules play out on a universe basis and it's fun yes yes

yes I get that I get that we'll go with that that's your titan at the Sheboygan Chucklehat I, okay. He hasn't spent enough time in Sheboygan. Neither abide. Monica, how will quantum computing help what you're doing? We don't know yet. Is there a problem that is intractable now that you think will succumb to quantum computers?

Well, certainly problems in atomic physics, like say the million different transitions in the molecule water that all produce different amounts of radiation of different colors. different spectral lines. Those may well be better done by quantum computing than the poor guy who came from banking into astrophysics and ended up having to do that for his thesis.

But most of the problems we have, we don't yet know how to compute on a quantum computer. Okay. Give it 100 years. A hundred? Oh. Or 10. I mean, don't know. I'm like, this is.

I mean, look. A hundred years ago, we were only inventing quantum physics. Yes, we had already invented quantum physics. And we're still figuring it out. Yes, we're still figuring out. It took, when Newton wrote down his laws of gravity, it took a century before we could explain the orbit of the moon. Yeah.

Yeah, okay. That's all the time we have, Naguene. Thank you for asking those questions. And Mordecai, brilliant answers, right on brand. Well. And you have some... Are you saying that I'm... using here?

I'm saying, plus you had at least one groupie there who was quoting you chapter and verse from 10 years ago. I was impressed. Thank you. Yeah, no, we, we, we, our people, our people go back.

Yeah, no, they're like, no things, the listeners. Yeah. Right audience to have. All right. This might be our first interview with you. This is my first time in this chair. In that chair, but not your first time

in my office. Not the first time in my, in this office. He works just down the hole. All right. Nagine, not your first rodeo here. No, my first time. And look forward to your next time joining us. Such a great time.

Thanks for having you. We'll find you on, wait, wait, wait, don't tell me. You find me a wait, wait, wait, don't tell me. If you're in Chattanooga, Tennessee on June 24th, you can find me there, too, at the comedy catch. Oh, Chattanooga, Tennessee. We'll look for you. And that's June 24th. June 24th, I'll be doing, the Muslims are coming with equally threatening friends, a night of stand-up comedy.

Okay. Will that attract people or scary people? If no one shows up in Chattanooga, Tennessee, we will know why. I need Dr. McLeod to do a simulation and see what happens. That's all the time we have. So, again, Mordecai, thank you. You're very welcome. Thank you. Great fun to be here. This has been StarTalk Cosmic Queries on the Formation of Planet with my friend and colleague, Mortykeye Mark McLeod. Until next time, keep looking up.