Relativistic beaming

Daniel and Kelly talk about how gravity, magnetism and relativity work together to create one of the most brilliant spectacles in the Universe. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

  This is an iHeart Podcast. Guaranteed Human.

• 0:04Speaker 01

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• 0:38Daniel Whiteson?

  Hey, Extraordinary's quick note for today's episode. I want to let you know about my new book, Do Aliens Speak Physics? It's all about whether or not we can use physics as a universal language to communicate with aliens, or whether physics is more human than many people imagine. And the book features cute cartoons of aliens from my friend, Andy Warner. If you've enjoyed my science outreach and wondered how you could support me, this is how. The book is out November 4th. Look for the link on the book website, www.alienspeakphysics.com. Okay, on to today's episode.

• 1:20Daniel Whiteson?

  Whenever we look out into the universe, we see something new that astonishes us. Something beyond our wildest imaginings of what the universe could do. It's a rich tapestry of extreme physics. And yet, all of it is described by physics. Deep down, the mechanisms that create black holes, or collide galaxies, or explode stars are rooted in the basic principles of physics. And so far, we've been able to come up with explanations for how these incredible events occur, and how the universe's vast and beautiful cosmos is shaped. Today, we're going to dig into the physics that underlies one of the most dramatic and literally brilliant phenomena in space: astrophysical jets. Welcome to Daniel and Kelly's extraordinary, brilliant universe.

• 2:19Kelly Weinersmith?

  Hello, I'm Kelly Wiener-Smith. I study parasites and space. And before looking at today's outline, I didn't know that astrophysical jets was a phrase that were a thing.

• 2:30Daniel Whiteson?

  Hi, Daniel. I'm a particle physicist. And if I had a baseball team, I might call them the astrophysical jets.

• 2:36Kelly Weinersmith?

  Oh, is that because your brain is fixating on the Astros part?

• 2:41Daniel Whiteson?

  It just sounds like a team that would score a lot of runs.

• 2:43Kelly Weinersmith?

  Yeah, yeah, no, and throw their balls really fast, I think. So when I was looking through the outline today, it occurred to me that this doesn't feel like it's in your main area of research. And so I was wondering if you could tell us, like, when you are researching something that you don't have knowledge of, like, right at your fingertips, what is your process like for preparing our outline?

• 3:06Daniel Whiteson?

  Yeah, well, that's fascinating, because this actually is sort of right on the edge of my area of research. I'm sort of a card-carrying particle physicist, which means that most of my career is like smash particles together at the Large Hadron Collider, see what new kind of stuff comes out. But I've always been super interested in space. And like many people, I got into it because of astronomy. But then I kind of discovered, like, hmm, astronomy is mostly standing around in the cold, looking at fuzzy things through a telescope. And that wasn't as exciting to me. Apologies to astronomy nerds out there who love that, and thank you for doing it. But it wasn't for me. But later in my career, I got re-interested in astrophysics, which isn't looking through a telescope, but it's like trying to understand the physics behind what's going on out there. Like, how does the star work, etc. So last

• 3:50Daniel Whiteson?

  few years, I've actually written some papers on the centers of galaxies, and neutron stars, and supernova, and stuff like this. But it is a little bit far from my core area of expertise. So it means reading a lot of papers.

• 4:04Kelly Weinersmith?

  Got it. How many are you reading?

• 4:09Daniel Whiteson?

  All of the papers.

• 4:11Kelly Weinersmith?

  All of them. Wow.

• 4:12Daniel Whiteson?

  I mean, what I try to do is find a review in that area, like find somebody who knows the field, who's written like a broad perspective, read that really carefully and then read a bunch of the papers it references to make sure I know like what's being summarized and what's actually going on and what's the sort of the lore, all this kind of stuff. It's a lot of work to try to really understand a new field well enough to try to contribute something to it. And, you know, I think you were asking though about like, if you want to talk about something on the podcast, not necessarily like write a bunch of papers about it. But I find like it's kind of similar to talk about something on the podcast, you got to understand it really well because my co-host is really smart and asks hard questions. And if I want to explain things correctly in a way that actually clicks in

• 4:55Daniel Whiteson?

  people's minds, I got to have it all up in my brain. So yeah, it means reading a lot of papers when it's not my area. Is that your experience also?

• 5:03Kelly Weinersmith?

  Yeah, yeah. When I'm working on my outline, I'm always asking myself, WWDA, which is what will Daniel ask? Trying to figure out like, what other things do I need to research that I am prepared for whatever Daniel asks?

• 5:17Daniel Whiteson?

  Yeah. I feel like everybody in my life who I get to know, I have sort of like a mini version of them in my head, like a little model of them, which constantly gets, you know, improved and updated. And of course, the most interesting people, it's never actually correct, which is why they can wonderfully surprise me. But I feel like that's a big part of understanding who somebody is, is like comparing them to like the little model you have of who they are and what they might say and how they might react. It's super fun.

• 5:42Kelly Weinersmith?

  Do the models in your, and then we should change subjects back to what we meant to talk about today. But do the models in your head, like, are they like miniature people that you see? Or are you just imagining their personalities without their bodies? I like, what, what do you imagine?

• 5:56Daniel Whiteson?

  Are they in the room with me right now?

• 5:58Kelly Weinersmith?

  That's right.

• 5:59Daniel Whiteson?

  I'm not schizophrenic, I'm pretty sure. No, just like you, I just ask myself, you know, what would my kid say in this situation? Or how would my wife react to having this for dinner? Or what would Kelly ask me if I said XYZ? You know, I think they're just useful for trying to understand who somebody is. But I also think it's helpful for understanding yourself, because you end up building also a model of yourself and turning that inwards. And anyway, I have my own bonkers theory of consciousness, but that's not what today's episode is about.

• 6:27Kelly Weinersmith?

  So when you sent me the outline for relativistic beaming, I was like, I just have zero clue what this means. So give us like some background, what we should expect in this episode.

• 6:39Daniel Whiteson?

  Yeah, this episode is about how the universe is constantly surprising us, how every time we look out into space, we see something new and weird, something that doesn't quite make sense. And yet, if we apply our knowledge of physics, it turns out we can crack it. We can make sense of, we can explain why it's happening. And often it gives us an incredible view of what's going on in extreme situations, you know, the cores of galaxies, when things are really hot and dense and fast. But it requires us to put together a lot of little pieces of physics, gravity, electromagnetism, even special relativity, in order to explain what we see out there in the universe. And so today's episode is the story of like several

• 7:21Daniel Whiteson?

  decades, almost a century of trying to understand some stuff we see out in space and finally putting it together. And the last piece of that is a process called relativistic beaming. And I had a bunch of listeners write to me and ask me about these astrophysical jets that are emitted from the centers of galaxies. And so I thought, let's do a deep dive into all the physics that makes those happen, especially that last bit, which I've never heard anybody cover with a popular treatment. So that was the motivation for today's episode.

• 7:51Kelly Weinersmith?

  Awesome. I'm excited about today's episode because I love those moments where like, you've studied a bunch of different topics that don't necessarily seem connected, but they turn out to be the building blocks that you need to understand something completely different that you probably wouldn't have been able to understand if you hadn't done all of that background, sort of foundational work ahead of time.

• 8:09Daniel Whiteson?

  Exactly.

• 8:09Kelly Weinersmith?

  So let's learn.

• 8:11Daniel Whiteson?

  All right. And so relativistic beaming is the last piece of it, but maybe the least well known. So I decided to go out there and ask our audience if they knew anything about relativistic beaming to help us calibrate. If you would like to participate for future episodes, please don't be shy. Write to us, [email protected]. In the meantime, ask yourself, do you know what relativistic beaming is? Here's what our listeners had to say.

• 8:37Speaker 03

  Relativistic beaming, I think that's when Chapman from the Yankees beams you in the head by accident. And if that happens with one of his fastballs, and when that happens, time will definitely go slower for you.

• 8:51Speaker 04

  So relativistic, relativistic beaming.

• 8:54Speaker 05

  Well, I can't remember off the top of my head. I think it was to do with synchrotrons when electrons are going near the speed of light and go around a corner. The, the radiation they release is very, is in a very tightly controlled spatial beam because of relativistic effects.

• 9:10Speaker 04

  Relativistic beaming is the ability of a thought to enter my mind and then instantly disappear as soon as I try to act on it. But in physics, maybe it's something to do with moving near massless particles near the speed of light and taking advantage of some of the relativistic changes that occur as a result.

• 9:30Kelly Weinersmith?

  I think my favorite answer, I mean, they were all great, but was how a thought enters my mind and then instantly disappears. Relativistic beaming in that sense happens to me like 50 times a day lately.

• 9:40Daniel Whiteson?

  Do you have that experience where you have an idea and then you try to write it down before it leaves your brain? And sometimes it's like no pencil or paper, you can't get to your phone and you're like, oh no, it's gonna go away.

• 9:50Kelly Weinersmith?

  Yeah, does it go away? Cause it does for me a lot of the time. Or are you just scared, but it stays?

• 9:55Daniel Whiteson?

  It absolutely does.

• 9:55Kelly Weinersmith?

  Okay.

• 9:56Daniel Whiteson?

  No, and then sometimes I have like the remnants of the idea. I'm like, I remember feeling this way about it and it was something about that. And what was it?

• 10:04Kelly Weinersmith?

  Yep.

• 10:05Daniel Whiteson?

  Man.

• 10:05Kelly Weinersmith?

  Yep, no, I, I'll think to myself, don't get distracted, don't get distracted while I'm looking for the pencil. And then I always think about like, oh, did we make Ada's lunch this morning? And then it's gone. And anyway, okay. So the thought that we do not want to forget is what is relativistic beaming?

• 10:20Daniel Whiteson?

  That's right. And the story starts with the things shooting out of the centers of galaxies. These things called astrophysical jets. If you have a mental image of a galaxy, you're probably imagining something like a disk. You've got a bunch of stars, they're all swirled together. And that's what the Milky Way looks like. And that's what Andromeda looks like. But there's another really important feature of galaxies that's not always visible to the naked eye. And these are the jets that shoot up and down from the poles of the galaxy out of the center. So instead of just imagining a disk, imagine a huge beam of light beaming up and down relative to the plane of the disk. These are astrophysical jets.

• 11:01Kelly Weinersmith?

  Okay. And so the jet is made of light. And just so I make sure I'm picturing that, because you said photons, right?

• 11:07Daniel Whiteson?

  Well, the jet has light in it. They are bright, but they're actually not just made of light. They're mostly plasma. So they're like high speed particles. There's electrons, there's protons, and there are photons as well.

• 11:18Kelly Weinersmith?

  Wow. Okay. So I'm, I just want to make sure that I've got my image of a galaxy correct. So at the center of our solar system, there's the sun. But at the center of a galaxy, there isn't necessarily some big thing. It's just, what is at the center of a galaxy? We talked about it maybe being a black hole, but we don't really know, right?

• 11:34Daniel Whiteson?

  Well, there are a lot of questions about what's at the center of the galaxy because it's hard to see. It's so dense there. You know, I think a lot of people have the image of a galaxy as like just a bunch of stars sprinkled around. But there's a big density variation, like the center of the galaxy is much denser than the outskirts. It's sort of like, you know, there's Manhattan, and then there's the suburbs, and then there's the exurbs. And we live kind of in the suburbs. It's not very dense, but it's not as rural as it is further out in the galaxy. But near the center, there's a lot of stars and there's a lot of gas and dust. So it is difficult to study the center of the galaxy. But we do know a lot about the centers of galaxies also by looking at other galaxies. And so far, every galaxy we've studied has a supermassive black hole at its center,

• 12:18Daniel Whiteson?

  with a couple of exceptions in cases where we're like, pretty sure the supermassive black hole has been ejected by like a recent collision or something.

• 12:26Kelly Weinersmith?

  You can eject a supermassive black hole? We've probably talked about this on a prior episode, and my bad memory is why life is so endlessly surprising to me. But whoa.

• 12:34Daniel Whiteson?

  Yeah. Well, when galaxies merge, what happens is the centers merge. It takes a long, long time. And then the black holes merge, but not always. And if you have like three galaxies merging at the same time, two of them can work together and eject the third one. And so, yeah, gravitational kicks can eject a supermassive black hole from the core. And it's not something we understand super well. We do think that there are supermassive black holes at the cores of these galaxies. So imagine a very, very dense center of the galaxy, and then fewer stars as you move away from the center. And then from the center, shooting up and down are these massive astrophysical jets. They can go for like hundreds of thousands of light years.

• 13:14Kelly Weinersmith?

  Wow. But they're not necessarily coming from the supermassive black hole, but just from like the general center.

• 13:20Daniel Whiteson?

  We're going to dig into that later in the episode, but we think they are connected, yes. And this was one of the central puzzles of astrophysical jets, and continues to be like, what exactly is powering them? It's a really fun question.

• 13:31Kelly Weinersmith?

  Okay, so stuff is shooting out. Is it just kind of like trickling out? Or is it moving really fast?

• 13:37Daniel Whiteson?

  These are some of the fastest things in the universe. Like, these jets are shooting particles out often very close to the speed of light. Like, the energy of particles in these jets is often much higher than energy of particles in our experiments here on Earth. Like, the Large Hadron Collider, we accelerate particles to have an energy of like around five to seven tera-electron volts. That's trillions of electron volts. But these galactic centers can accelerate particles to much higher energies, which connects to lots of fascinating mysteries. Like, we see super-high-energy particles arriving on Earth, and we don't understand where they come from. And one theory is that they're being kicked to super-high energy by these galactic accelerators, essentially.

• 14:21Daniel Whiteson?

  That these centers of galaxies are like enormous guns, shooting out particles at super-high energies.

• 14:28Kelly Weinersmith?

  But then you, so you shoot the particles out? And then where do they go? What happens to them?

• 14:35Daniel Whiteson?

  Well, if you believe that it's natural, right? And there's really fun theories out there about how like, maybe aliens have mega-structures, and they're engineering the centers of galaxies to do particle physics experiments.

• 14:44Kelly Weinersmith?

  What?

• 14:45Daniel Whiteson?

  That would be awesome. Two galaxies pointing at each other. But in general, they just shoot out into the universe. And you can see these astrophysical jets, if you look at it in the right spectrum. Really beautiful. You should Google these images. They're spectacular. Often, these things are bigger than the galaxies themselves. They just shoot out into the universe, and then, you know, there are magnetic fields out there in the universe, and these are mostly charged particles. And so, they bend and they fly around. And one reason why we like to study the cosmic rays, the super-high-energy cosmic rays, is that they are less bent than the other particles. So, you want to know where something came from? If it's like gotten bent and zipped around and changed direction 100 times, it's hard to tell. But if it's come mostly straight at you, and high-energy particles get less bent by

• 15:29Daniel Whiteson?

  magnetic fields, then it's easier to sort of point back in the sky and say where it came from. So, that's one reason why we look for the super-high-energy particles, because they tend to point back to their source more than lower-energy particles.

• 15:41Kelly Weinersmith?

  Yeah. Very cool. Okay, so they're going really fast. It's a lot of different stuff. Is this like a narrow beam? Or is this like pretty wide and spread out?

• 15:50Daniel Whiteson?

  It's pretty narrow. Like when they were first discovered, and we'll dig into that. These are little sources, like in the sky. They're pretty small, which is one reason why it was such a puzzle. And it's it's sort of amazing. And, you know, you have these galaxies and they're emitting these things up and down the north and south pole from the center. And it's fascinating because it's not shot up by the supermassive black hole itself. Obviously, black holes do not emit photons. It's not like, you know, black holes are shooting particles out into space or anything like that. But the environment the black hole creates, and in general, the environment of the galaxy, might be the thing that's powering these particles and creating these beams.

• 16:31Kelly Weinersmith?

  Awesome. So we we've gotten to the what? And now we're going to take a break and then we'll get to the why. Why do you get astrophysical jets, not the baseball team?

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• 17:18Speaker 07

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• 17:38Speaker 08

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• 19:03Kelly Weinersmith?

  All right, we're back. We've described astrophysical jets and now Daniel's going to help us understand why you get these bursts of loads of different kinds of things coming out of the center of galaxies.

• 19:13Daniel Whiteson?

  Yeah, and I think a fun way to attack this is to take us through the history in the last century of people trying to understand them and putting together lots of different things simultaneously. Because astrophysical jets are connected to something else we've probably heard about, which are quasars. Let's put astrophysical jets in our pocket for a minute and talk about the history of quasars, why they were confusing, how we understand them, and then how they come back together to help us understand astrophysical jets.

• 19:42Kelly Weinersmith?

  Let's get into the quasar question.

• 19:44Daniel Whiteson?

  So quasars are fun because like the word itself is like, sounds super cool in science fiction and they're named because we didn't understand what they were. Right. So quasars are short for quasi stellar objects. And they were first found back in the 1950s when we didn't really understand a lot about the galaxy. It was only like 20 or 30 years since we understood that there were other galaxies out there in the universe. And we started studying these things they called nebula that turned out to be other distant galaxies. And then in parallel, we had the birth of radio astronomy. And astronomy used to be just in the optical, like you look through a telescope and you see, what do I see out there? And let's make a map. But radio and World War II led to the advent of radio telescopes, people listening to

• 20:28Daniel Whiteson?

  the sky in the radio. And what they found were these radio sources in the 1950s where they couldn't find any optical object as well. They were like, hmm, there's something out there that's emitting in the radio, but the telescopes at the time couldn't see anything there in the visible. So they're like, what are these things?

• 20:47Kelly Weinersmith?

  So then are they quasi objects? Cause they're like, maybe that's from space. I don't know. Maybe we messed something up. Like, why, yeah, why the quasi part?

• 20:55Daniel Whiteson?

  Yeah, exactly. They didn't understand what they were. So they're like, maybe there's something like stars because they're sort of localized, but there's no visible object there initially. So it was a real mystery at first, which is why I think they went for like, let's give this kind of a fuzzy name. So we don't, we don't paint ourselves in the corner, which hey, maybe that was wise.

• 21:14Kelly Weinersmith?

  Oh yeah. So maybe after they figured out what it was, they should have called it like straight up stellar objects. Like, we're totally sure about this.

• 21:20Daniel Whiteson?

  But they're not stars, right? They're not stars. So it was good that they left that fuzz.

• 21:25Kelly Weinersmith?

  Oh, so stellar means star, not just like spacey?

• 21:27Daniel Whiteson?

  Yes, exactly. Something like a star. Yeah.

• 21:30Kelly Weinersmith?

  Yeah. Kelly is really good with words. All right. Moving on.

• 21:36Daniel Whiteson?

  And they knew that they had a very small angular size, right? Like they could tune their radio telescopes in a certain direction and see it, and then turn it a little further away and not see it, right? And so you could tell that this thing was coming from a localized spot in the sky. And by the sixties, there were like hundreds of these things had been catalogued. And so people started a dedicated search for like, let's look to see if we can find something that corresponds to them. And then in the early sixties, they finally found one. They found like a, what looked like a faint star right at the location of the radio source. But the spectrum of it didn't really make sense. It was very confusing to understand like what this object was.

• 22:15Kelly Weinersmith?

  What was it? It was the quasar. But then what is a quasar?

• 22:19Daniel Whiteson?

  And what is a quasar? That was the question, right? So first thing they did is look at the spectrum and they noticed like, hmm, this spectrum implies that it's really, really, really redshifted, meaning that it's really, really far away. Because remember, as we look out into space, we're not just looking back in time. We're looking at things that are moving away from us. Hubble's big discovery was that the further away something is, the faster it seems to be moving away from us. And so if you find something which is super redshifted, meaning it's moving away from us very fast, that also means it's super distant. And that was one of the early puzzles. It's like, okay, we're seeing this star. It's not super bright, but it's crazy far away, which means that at its source, it's got to be like insanely bright for us to see it.

• 23:04Daniel Whiteson?

  These things were apparently like most of the way across the universe. And yet somehow we were still seeing them. So people were like, wow, what? This doesn't make sense. If our calculations are correct, there's an incredible source of energy being shot at us from across the universe. How can that be right?

• 23:21Kelly Weinersmith?

  Yeah. How can that be right? It's like a murder mystery. I'm waiting for the end.

• 23:26Daniel Whiteson?

  Exactly. And so you have this combination of like extreme velocity and distance, yet we're able to see it. And this implies some intense source of power, right? You need something in order to generate something to make these things brighter. Essentially, it would have to be like a thousand times brighter than the entire Milky Way for us to see. See it across the universe. So we're talking like three billion light years away. And so the early explanation was that you have an active galactic nuclei. So the the centers of the galaxies are not just like, here's a bunch of stars all swirling around. And they're just sort of denser than they are out here, but that there was something else going on.

• 24:07Daniel Whiteson?

  And this is essentially at the same time as we're starting to understand, hey, are black holes a real thing? They're not just like a calculation that Einstein and his friends did, or like an actual thing out there in the universe. And so this all came together into this cohesive explanation that the center of the galaxy is very dense gravitationally. And you have these supermassive black holes at their cores. And the gravity of that supermassive black hole, combined with its magnetic field, is generating these astrophysical jets.

• 24:39Kelly Weinersmith?

  Okay, so a quasar is the center of a galaxy where you have a black hole and all of that denseness and stuff is shooting out?

• 24:45Daniel Whiteson?

  Yes, exactly, as seen from Earth. So like, you could describe it in several ways. You could say you have an active galactic nucleus, which is generating these jets from Earth. If you see it, you call it a quasar. And so it's sort of the union of these things as seen from different angles.

• 25:00Kelly Weinersmith?

  So does every galaxy have a quasar?

• 25:03Daniel Whiteson?

  No, every galaxy does not necessarily have a quasar.

• 25:06Kelly Weinersmith?

  What?

• 25:06Daniel Whiteson?

  It's fascinating. Not every galaxy has an active nucleus, right? It's really interesting.

• 25:12Kelly Weinersmith?

  And is that because not every galaxy has a black hole at its center, maybe? Or this is a different reason?

• 25:18Daniel Whiteson?

  We don't know. It's a real mystery. It seems like the universe made a lot of quasars about 10 billion years ago. And since then, it hasn't been making very many of them. So like, that's why most of them are far away. Like, there aren't quasars that are like quasaring right now nearby. Like, the Andromeda doesn't have a quasar. It doesn't have massive bright poles of plasma shooting out from both sides of it. You have to look further away, which implies that it was in the past. So there was something in the conditions of the universe 10 billion years ago, which was really quasary. And it's no longer, is the universe very quasary?

• 25:54Kelly Weinersmith?

  It's like the fashion of the universe, like neon leggings were big in the 80s and quasars were big at some point, but both went out of style.

• 26:01Daniel Whiteson?

  Yeah, exactly.

• 26:03Kelly Weinersmith?

  But the leggings are coming back. Maybe quasars will come back.

• 26:06Daniel Whiteson?

  Yeah, nostalgia for the early universe. I don't know, these things are dangerous, right? So it's crazy. The oldest quasar we've seen comes from a galaxy we visualized 690 million years after the Big Bang. So it's less than a billion years after, you know, the first atoms are formed and then finally stars are formed and then galaxies come together and already you have the conditions necessary to create a quasar. And this is one of the bigger puzzles in the early universe recently is like how things got so big so fast, you know, how did you get super massive black holes at the centers of galaxies so quickly after the beginning of the universe? Our simulations can't explain that. James Webb

• 26:49Daniel Whiteson?

  Space Telescope, which looks in the infrared, can see super distant, super old stuff and it's visualized galactic formation that nobody understands either. Like very early in the universe, you have galaxies that are much bigger than anything we can understand. So this is a core question. It's like, how does stuff come together and form structure in the early universe so quickly? There's definitely an element there that we don't understand and quasars are a big part of that. Why did they come up in the early universe? Why aren't they making them anymore?

• 27:18Kelly Weinersmith?

  Why did they go out of style like the fashion in the 80s, which I would say was a really good era. So, okay, so the jets are different than the quasars. The jets come out of the quasars. And so why are the quasars making the jets?

• 27:31Daniel Whiteson?

  Yeah, I would say quasars are the thing we see from Earth, right?

• 27:34Kelly Weinersmith?

  Okay.

• 27:35Daniel Whiteson?

  The jets are the sort of underlying physical process that generates our observation of the quasar. But you're right, it's a good question. What is making these jets? They're super bright, they're super intense. We think they are powered by this active galactic nuclei and fundamentally, the black holes at their cores, right? These are super massive black holes. And remember, black holes come in two categories. There's like, there's a star that burned up all of its fuel and the fusion is no longer providing pressure to keep that star puffed up. And so the gravity eventually wins and it collapses and you get a black hole. That's going to give you a black hole up to like 50, 80, maybe 100. Times the mass of our sun. But the black holes at the centers of galaxies, these things are like millions or billions of times the mass of the sun.

• 28:20Daniel Whiteson?

  So definitely not the collapse of an individual star. And again, a big mystery as to how they form. But they're enormously massive and they're at the centers of these galaxies. And we think that the gravitational energy of these black holes, as well as their spin, is what's powering these astrophysical jets.

• 28:37Kelly Weinersmith?

  All right. So as a biologist,

• 28:39Daniel Whiteson?

  Yeah.

• 28:39Kelly Weinersmith?

  it's counterintuitive to me because I feel like the main thing I know about black holes is that they like suck things in if it gets close enough.

• 28:46Daniel Whiteson?

  Yeah.

• 28:46Kelly Weinersmith?

  And so now we're talking about stuff getting seemingly spit out of black holes. So what bridged the gap there for me?

• 28:53Daniel Whiteson?

  Yeah, it's a good question. And remember that black holes are super gravitational and powerful, but they're not magical, right? They're just like suck everything in. You can, for example, orbit a black hole the way you can orbit the sun, because the gravity from a black hole is just gravity. So if you're at the right velocity and at the right radius, you can orbit a black hole forever. It's not going to magically suck you in. So let's think about how black holes at the centers of galaxies work. Well, you have the black hole, then you have stuff swirling around it, right? So that stuff could, in principle, stay in orbit forever. So just because it's near the black hole doesn't mean it's going to get sucked in necessarily. And that's why you have like this accretion disk. If you think about your image of a black hole, it's not just like a black sphere.

• 29:36Daniel Whiteson?

  There's like a disk of stuff that's orbiting around it. That's the stuff that's like on deck for going into the black hole, hasn't fallen in yet. All right. So why does it actually fall in? It falls in because there's friction. Like if you're just orbiting a black hole or a star, you could do that forever. But if you and 10 trillion of your friends are all orbiting a star, you're going to bump into each other and occasionally somebody's going to get nudged into the center, right? Out of orbit. That's what an accretion disk is. It's like a huge cloud of gas and dust and little bits. And there's friction between them. They bump into each other. They pull on each other gravitationally. So some of this stuff falls in. All right. So particles are now falling in towards the black hole. But black holes also have magnetic fields. They're not just gravitational objects.

• 30:24Daniel Whiteson?

  And what do magnetic fields do? They bend the path of charged particles. Think about particles coming from the sun towards the earth. What happens to them? They don't just hit us down here on the earth. They get deflected by the magnetic field. And they get deflected towards the north pole and towards the south pole. And some of them, because the magnetic field is different at the north pole, go into the atmosphere there, which is what causes the northern lights or the southern lights. Those are super high energy particles from space hitting the atmosphere and then glowing.

• 30:54Kelly Weinersmith?

  Gorgeous.

• 30:54Daniel Whiteson?

  Yeah, and so just like the earth has gravity, but also has a magnetic field, particles falling into the black hole will get deflected up towards the north pole or the south pole because of the super intense magnetic field. And so they get sped up by the gravitational field and then they get bent by the magnetic field and then shot up or down the poles.

• 31:14Kelly Weinersmith?

  Ah, okay, so everything that's getting shot out then has some charge.

• 31:18Daniel Whiteson?

  Yes, almost everything here is going to be charged because it's very hard to stay neutral. Like if you have protons and electrons and they're in hydrogen atom, the energy of that bond is tiny compared to the energy of these particles. And so they're just going to blow apart, right? So basically, everything is plasma here, everything is charged. And so you get plasma, they get shot up and down the north and south poles, and plasma itself glows. So where do the photons come from, right? Photons come from these particles getting bent by the magnetic field. Because how does a charged particle change direction? Every time a charged particle change direction, it emits a photon. That's the only way you can do it. You can't just be like, I'm going this way, now I'm going that way. The way it does it is by emitting a photon.

• 32:00Daniel Whiteson?

  It's like, I'm going straight, I want to go right, I'm going to emit a photon to the left. Therefore, I'm going to recoil against it to the right. Just like if you're flying through space and you want to change direction, what do you do? You fire your rockets and you shoot some stuff out in the opposite direction that you want to go. Charged particles have to do that also. And they shoot out photons, they have like an infinite supply of photons inside of them. You can imagine, they don't literally have all those photons. They just, you know, dump some of their energy into the electromagnetic field with momentum in the opposite direction that they need to go. And so then they go that way. And there's nobody like driving these particles. I'm making them sound like they're making these decisions, but this is just the process. Anyway, so stuff falls in towards the center,

• 32:44Daniel Whiteson?

  gets routed towards the poles using a magnetic field. And that's how you get these jets. And the power comes from the gravitational energy of the black hole.

• 32:52Kelly Weinersmith?

  So the centers of galaxies that have astrophysical jets are only the centers of galaxies that have a black hole in the middle. Is that fair to say? Because you need the black hole's magnetic field?

• 33:04Daniel Whiteson?

  Yeah, exactly. And that's because almost every single galaxy has a supermassive black hole at its heart.

• 33:11Kelly Weinersmith?

  Okay.

• 33:11Daniel Whiteson?

  So it's pretty safe to say, anyway.

• 33:13Kelly Weinersmith?

  And do all black holes make these jets?

• 33:15Daniel Whiteson?

  Yeah, that's a great question. And so some of these active galactic nuclei have all the conditions, we think, for making a jet, but they don't have jets. Right? There is a big, powerful black hole there. There's a swirling mass of gas and dust and particles, but there's no jet. And so, as we said earlier, this is not something we currently understand. And there's a lot of current research on, like, understanding the magnetic environment around a black hole, because it's funny to even think about, like, well, why do black holes have magnetic fields, anyway, right? Aren't they gravitational objects?

• 33:47Kelly Weinersmith?

  Yeah. Why?

• 33:51Daniel Whiteson?

  Black holes are really weird things, and there's only three things that they can have. They can have a mass, right? You can put stuff into a black hole, and it grows, so its mass increases. But they can also have an electric charge, right? Like, what happens if you have a black hole, and it's neutral, and you drop an electron into a black hole? Well, now it has a charge, because the universe conserves electric charge. It can't just eat the electric charge, and then, boom, it's gone. You've deleted it from the universe. The universe conserves electric charge. So if you drop an electron into a black hole, we don't know what happens to that electron. Is it still an electron, whatever? Is it something else? But we do know that that charge is now added to the event horizon. So we don't know what's going on inside the black hole, but you can think of the event

• 34:34Daniel Whiteson?

  horizon itself now as charged.

• 34:37Kelly Weinersmith?

  So do most black holes have a negative or a positive charge? Or is it, like, split 50/50? What is the predominant charge of black holes?

• 34:45Daniel Whiteson?

  Yeah, great question. Most black holes have either a positive or a negative charge. It's about split 50 50. We think we haven't measured this in detail for any black holes. But you know, imagine that you randomly throw in positive and negative particles, and you do it a billion times. In order for the black hole to be neutral, those would have to be exactly equal. It's like flipping a coin a trillion times and getting exactly half of them to be heads and exactly half of them to be tails. Very, very unlikely. So we think there probably are no electrically neutral black holes in the universe. Probably every black hole out there has some charge because it's eaten positives and it's eaten negatives. And the chances that they add up exactly to zero, basically zero.

• 35:27Daniel Whiteson?

  So now you have a black hole has gravity, has mass, and has electric charge. There's one more thing black holes can have, which is spin, because the universe also conserves angular momentum, right? Momentum is just like if you're moving through space. Newton tells us that you can't just move without something pushing you, or this conservation of momentum. Well, spin is also conserved. If you like, set something spinning in space, it'll spin forever. The only way to stop is to come with some external torque. Same thing is true if you drop something into a black hole. Instead of just dropping an object straight in, imagine if you drop an object, so it hits the black hole like sort of near the edge. Sort of like spinning a bicycle wheel, right? Pushing on the edge to make it spin rather than poking it in the center.

• 36:12Daniel Whiteson?

  Same thing, if you drop an object into a black hole, you can make it spin, and it conserves that spin. The universe can't just get rid of angular momentum. So now you have an object which has an electric charge and it has a spin. What happens with that?

• 36:25Kelly Weinersmith?

  You've got a magnetic field!

• 36:27Daniel Whiteson?

  Boom! Oh, my gosh! Congratulations!

• 36:30Kelly Weinersmith?

  Woo! P O D in physics!

• 36:32Daniel Whiteson?

  Exactly. And because magnetic fields are not generated by magnetic charges, we don't know if monopoles exist in the universe, right? The only way to make a magnetic field in our universe is to combine electric charges and motion. So currents generate magnetic fields, spinning objects generate magnetic fields. So, black holes have magnetic fields, and this is fun to think about. The way I visualize it is that I put the charge and spin on the event horizon. We don't know what's going on inside. This way you don't have to worry about like, how is the information getting from inside the black hole to the outside? Just imagine a spinning sphere of charge. And that generates a magnetic field. The Event Horizon is conceptually similar to that.

• 37:14Kelly Weinersmith?

  Okay, so all black holes, it sounds like all black holes should have magnetic fields because probably none of them are neutral.

• 37:21Daniel Whiteson?

  Exactly.

• 37:22Kelly Weinersmith?

  But they don't all make the jets. Is that because some of them have stronger magnetic fields than others? Or we really don't know?

• 37:29Daniel Whiteson?

  We really don't know. Yeah, it's a mystery. Active galactic nuclei, hot area of research, and definitely not something we understand. But you know, when they do this, it's really dramatic. One other way to study these things is not to look for the active galactic nuclei, but to try to study the black holes and their magnetic fields in more detail. And so, for example, we have image black holes, a couple of them, right? Remember these pictures that look like a Krispy Kreme donut of the accretion disk around a black hole? Super awesome from the Event Horizon Telescope. That's the stuff that's swirling around the black hole, waiting on deck maybe to go in. Well, a few years after they released that image, they released a follow-up image where they studied the

• 38:10Daniel Whiteson?

  magnetic field lines near the black hole. By looking at the polarization of the photons that come from different parts of the accretion disk, they can understand the magnetic fields. And polarization of photons is kind of weird. It's because photons are vector objects. They're not just like a location in space. They also have like a direction. And so they can essentially spin as they move. And so photons have like this little vector, extra vector that you can measure. We don't have to dig into the details now, but we are studying the polarization of these photons that come from the vicinity of black holes and trying to understand which models of magnetic fields in the vicinity of black holes make the most sense, best agree with the data with what we see out there in the universe.

• 38:55Kelly Weinersmith?

  Cool. All right. So let's take a break. And we've talked about astrophysical jets. And I realize that in my head, I've decided that that is what relativistic beaming means. But maybe that's not actually true. So let Daniel shaking his head no. So let's clear up Kelly's misconceptions after the break.

• 39:20Speaker 01

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• 39:51Speaker 07

  Hey, it's Niall Rogers, host of Before the Moment, a Lincoln original series. I'm driving across the country, meeting some of today's most fascinating artists. We're exploring the stories before the moment that changed everything. This week, I'm joined by my friend, John Ledge. What still makes you just sit down at the piano?

• 40:13Speaker 10

  If you sat down at 9:00 AM and then at noon, you had a full song that you recorded and put in your voice recorder or you recorded at your studio. You've just created something brand new that didn't exist when you woke up. What a beautiful feeling it is. I'm always excited to write something new. I've been writing for Broadway, which has been a new challenge with new collaborators and amazing performers who are triple threats, who can sing and dance and act and do all these amazing things. And I want to keep feeling that. And so that means not resting on my laurels, going out there and continuing to create something new.

• 40:49Speaker 07

  Experience Before the Moment, a Lincoln original series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

• 40:57Speaker 09

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• 41:40Kelly Weinersmith?

  All right, so astrophysical jets are those things that get shot out of quasars that have black holes, but not all of them. And I thought that this resulted in relativistic beaming, like the beam that comes out of the center is, but no, you shook your head no. So what is relativistic beaming, Daniel?

• 41:59Daniel Whiteson?

  Yeah, so we have these astrophysical jets. We understand something about how they're made. They're extraordinarily powerful. We used to call them quasars when we saw them in the sky. And we see them all over the universe. There's lots of them that we've spotted. We've, I think, identified 750,000 different quasars in the universe, which is a lot. Most of them are not pointed at us, right? So we can see them even if they're not pointed at us. And the most dramatic pictures you'll see online are ones we see sort of from the side. We can see them from the side because they emit photons also from the side. They hit each other and they glow, et cetera, et cetera. But the brightest ones are the ones pointed right at us. Like if there's a galaxy out there that's oriented perfectly,

• 42:41Daniel Whiteson?

  so we're looking at exactly at the plane of the galaxy, and the core of the nuclei is pointed like directly at the Earth, then those particles are shooting exactly towards us when they're emitted from the galaxy. And then they benefit from a super awesome, extra special boost that makes that galactic core even brighter than it otherwise would be. And that's relativistic beaming.

• 43:07Kelly Weinersmith?

  Ah, okay. So it's not brighter just because it's pointing at us, making it easier to see. It's brighter for some other reason?

• 43:13Daniel Whiteson?

  That's right. It is brighter because it's pointing at us and that makes it easier to see. But plus, it gets souped up because of this relativistic effect, which you could also consider to just be like the relativistic version of the Doppler effect, right? Anything that's moving towards you is going to get blue shifted. Anything moving away from you is going to get red shifted. And it's easy to understand that. It's something we experience every day. If you like hear a police car drive by you, you hear the sound that its siren makes changes as it passes you, right? When it's approaching, it's a higher sound. When it's moving away, it's a lower sound. Why is that? It's because the wavelength gets shifted to longer wavelengths when it's moving away from you. All right, if you just imagine like a source moving away from you, it's going to draw out

• 43:58Daniel Whiteson?

  longer wavelengths than a source moving towards you. And so each wavelength is a little bit shorter. That's the generic Doppler effect. Things moving away from us are redshifted, which is also how we can infer distance because there's a relationship between redshift and distance in the universe. Things moving towards us are blue shifted. And we see this in the sky, like not everything in the sky is moving away from us. Andromeda, for example, is overcoming the expansion of the universe. A local gravity is pulling it towards us. So Andromeda in the sky is blue shifted, not red shifted. Okay, so that's the Doppler effect, which is something fairly well known. But special relativity changes everything, right? Normal Doppler effect is what happens when things are pretty slow and not moving super fast, like the way I move here on Earth, right? Especially now that I'm 50 years old.

• 44:43Kelly Weinersmith?

  You're a spry 50, Daniel.

• 44:46Daniel Whiteson?

  Thank you. Astrophysically speaking, I'm quite young.

• 44:49Kelly Weinersmith?

  That's right.

• 44:51Daniel Whiteson?

  These quasars make me feel like a spring chicken.

• 44:55Daniel Whiteson?

  But when relativity comes into play, things change. And astrophysical jets are moving near the speed of light relative to us. And so they benefit from the relativistic Doppler effect, which super enhances the brightness in the direction of motion, the energy of these things in the direction of motion for two reasons.

• 45:14Kelly Weinersmith?

  Reason one.

• 45:18Daniel Whiteson?

  And reason number one is our old friend, length contraction. And the rule of thumb for length contraction is moving objects seem shorter. So if you're just like looking at a ruler and it's sitting next to you, you measure it's a meter long. If instead it's zooming towards you at nine tenths the speed of light and then you measure it, you're not going to measure it to be a meter long. You're going to measure it to be less than a meter. Moving objects are shorter.

• 45:42Kelly Weinersmith?

  Okay.

• 45:42Daniel Whiteson?

  And that's a super fun and mind bending consequence of special relativity, which I love thinking about. And people often ask me like, well, why is it shorter? And you know, I think that's a really revealing question because the answer is it only actually makes sense for it to be shorter. In a universe where the speed of light is fixed for all observers, it has to be shorter. It wouldn't actually make sense to measure that meter stick as a meter if it's moving. But our intuition is that speed shouldn't change the length of things. Kelly thinks, oh, when my daughter's running across the yard, she's the same person, the same size as she was when she was standing still. And mostly she is almost, she is, you can't tell, which is what gives us this intuitive feeling that

• 46:26Daniel Whiteson?

  length shouldn't depend on velocity. But we're wrong. It actually does. There's no good reason why length shouldn't depend on velocity. So this question like, why does length depend on velocity? Reveals again, just our bias towards things we find intuitive. If I told you, oh, length doesn't depend on velocity, you wouldn't ask me why. You'd just be like, yeah, cool.

• 46:49Kelly Weinersmith?

  Makes sense.

• 46:50Daniel Whiteson?

  Anyway, that's a digression on special relativity. But in this case, what's happening is the thing is shooting right at us, moving very, very high speeds, right? So from the point of view of that object, the distance between it and the earth is contracted, right? Because it sees the earth moving towards it at really high speeds, right? So we're seeing it as if it was closer, right? So relativity is like shrinking the distance between us and the center of this galaxy, this furnace where the black hole is shooting bullets at us at super high speed, it's bringing us closer to that.

• 47:22Kelly Weinersmith?

  And that's what makes it brighter.

• 47:23Daniel Whiteson?

  That's one of the things that makes it brighter. Yes, that's reason number one. And that's why it's called relativistic beaming, because it's like the relativistic Doppler effect is making this much brighter if it's pointed at you.

• 47:35Kelly Weinersmith?

  That's amazing that we figured that out, because you'd look out at the sky and you'd be like, some quasars are brighter than the other. But like to account for that, anyway, go humans.

• 47:43Daniel Whiteson?

  And that's why I started this episode with like, to understand this, you got to understand gravity of black holes, you got to understand magnetism of the bending, and then you got to bring in the relativity to show why these things are so bright.

• 47:54Kelly Weinersmith?

  So many blocks. All right. Reason two.

• 47:58Daniel Whiteson?

  Reason number two is the other fun bit of special relativity, which is time dilation, right? So special relativity tells us that moving objects look shorter, but also that moving clocks run more slowly, right? And so what's happening when you're looking at a quasar is relativity changes the frequency of these things, right? We talked about how you go from redshift to blue shift, depending on the velocity. Well, changing the color, changing the frequency, also changes the energy, right? And so if these things are blue shifted, that makes them more energetic. So the particles are not just pointed at us, they're moving at us at very high speed. And relativity boosts that to make them have more energy in our frame. And that's a confusing thing to think about,

• 48:43Daniel Whiteson?

  like, how does relativity give something more energy? Remember that energy is conserved in a static universe. It's not actually conserved in our expanding universe, but it's not invariant. Meaning like, I can measure the energy of something and you can measure the energy to be different. If your daughter is running past you on the lawn, you measure her to have a certain velocity, a certain kinetic energy. If your husband is running next to her, he says, no, she's not moving at all. She has no energy. So you two can disagree on how much energy she has because energy is frame dependent. We think it's conserved in a static universe, but it's not invariant, which often leads to confusion. So you and I can disagree about how much energy something has. And the energy of these astrophysical jets depends on the observer because energy is frame dependent.

• 49:28Daniel Whiteson?

  It's relative. It's not an absolute quantity.

• 49:30Kelly Weinersmith?

  Okay, okay. And so while you were describing this, I realized that, so we're talking about charged particles moving super fast towards us. Is this galactic cosmic radiation? Is this what the astronauts have to worry about?

• 49:43Daniel Whiteson?

  This is one source of that, absolutely, yeah. And when you're out there in space near the ISS, for example, this is one of those elements. You're absolutely right. It's a dangerous environment. And that partially comes from the sun and partially comes from inside our galaxy and partially comes from other galaxies. We think the highest energy ones come from the centers of other galaxies.

• 50:04Kelly Weinersmith?

  Whoa, okay. So, so I should be saying that galactic cosmic radiation comes from quasars? No, from astrophysical jets.

• 50:11Daniel Whiteson?

  Or quasars, yeah, either one works.

• 50:13Kelly Weinersmith?

  Okay, and they're super bright because of relativistic beaming.

• 50:16Daniel Whiteson?

  Yes, absolutely. They're super bright even without the relativistic beaming, but then they're super double extra bright because of the relativistic beaming. The ones that are pointed right at us get super enhanced because of these relativistic effects. So it's this incredible dance of all these pieces of physics. And it took us decades to put this all together. And so many different branches of physics and so many different historical traditions came together for us to like, start to understand a coherent picture of what's going on inside galaxies. And that's such an important thread in science, you know, is understanding things from different perspectives and like, making sure the story you're telling is coherent when you come at it from different angles. And that's often how we unravel mysteries, right? We're like, well, this seems to work, but wait, what about this piece?

• 51:01Daniel Whiteson?

  If I measure it differently, if I come out from this angle, it's not making sense. Because we think, we hope, the universe does make sense and that there is a story out there that we can unravel, no matter how you look at it.

• 51:12Kelly Weinersmith?

  And I really love human stories. So let me tell an astronaut story really quick. So when I was reading astronaut memoirs, there's a lot of times where they'll talk about like, being in space and then like, a flash of light, it's like it passes through their eyeballs. And they were kind of not sure what it was. It's probably kind of a scary experience. And I think that the main hypothesis to explain what's happening is that galactic cosmic radiation is passing through your eyeballs and it like, lights up, you know, the receptors in your eye. And that's what you see. It's kind of-

• 51:44Daniel Whiteson?

  That's scary.

• 51:44Kelly Weinersmith?

  Yeah. One, super scary. Two, kind of amazing, though, to think that your, you know, vision is being impacted by something happening in a quasar on a distant, you know, galaxy. Anyway, what a crazy universe we live in. Also, I like it down here on Earth.

• 52:01Daniel Whiteson?

  I know, it is nice to live here beneath the shelter of our magnetic field and our atmosphere.

• 52:06Kelly Weinersmith?

  Yeah.

• 52:07Daniel Whiteson?

  Where our eyeballs are not getting pelted by bullets shot out by black holes from other very distant galaxies.

• 52:13Kelly Weinersmith?

  Thank you, magnetic fields, protecting our Earth.

• 52:15Daniel Whiteson?

  Thank you, our fragile environment. And thanks to everybody out there for being curious about how the universe works and listening to this explanation for how the centers of distant galaxies combine gravity, electromagnetism, and relativity to shoot particles at you.

• 52:33Kelly Weinersmith?

  See y'all next time.

• 52:41Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 52:47Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 52:53Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 52:59Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 53:06Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 53:15Daniel Whiteson?

  Don't be shy. Write to us.

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• 53:47Speaker 12

  Hey, it's Covino and Rich Davis from Covino and Rich. Buy smart, drive for less, and trade for more. That's Toyota affordability. And it starts with a great deal on an off-road ready Tacoma or half-ton Tundra, two of Toyota's most capable and longest-lasting trucks. Combining power for work, tech for adventures, and style in between. Built on reputation for quality and reliability, Toyota trucks are known for holding their value, which can mean big savings when it's time for your next Toyota. So get a great deal today and great value tomorrow. Shop toyota.com for more. Toyota, let's go places.

• 54:22Speaker 07

  Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything. Because every musician remembers the moment where it all began. Experience Before the Moment, a Lincoln Original Series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

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