Science

Supermassive Black holes

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Collin Sinclair: Oh, hey! Welcome back to “A View From Earth” brought by the Fiske Planetarium at CU Boulder! We hope you’re all staying safe and doing well. Collin Sinclair: As with the rest of the university, and many public spaces around the world, Fiske’s theater is closed to the public for the foreseeable future due to the COVID-19 epidemic. Collin Sinclair: However, we are still so committed and excited to bring astronomy and education to you that we’ve started a whole host of free online offerings so that we can stay connected and keep bringing you the Fiske content you know and love. Collin Sinclair: Plus some new stuff, like this podcast! So thanks for tuning in and learning with us here today. Collin Sinclair: My name is Collin Sinclair and I am a CU student, I am a presenter at the Fiske Planetarium and I am co-host of this podcast.

Tara Tomlinson: And my name is Tara, Tara Tomlinson. I am a planetary scientist and a CU alum and also a presenter at Fiske Planetarium. I also coordinate our community outreach program Tara Tomlinson: and obliously co-host the podcast as well. Collin Sinclair: This week, we’ll be talking about Black Holes! Collin Sinclair: Now these are some of the most intriguing and elusive objects in the universe, and astrophysicists have done an amazing job of studying them and sharing their findings. Collin Sinclair: Today’s guests are Jimmy Negus and Dr. Andrew Hamilton, and they’ll be answering the questions: “What is an Active Galactic Nucleus?” and “What is the interior of a black hole like?”! Collin Sinclair: But first, the news… Tara Tomlinson: Alright, so for our new segment this week, we have our friend rainy here with us rainy once you introduce yourself a little bit about you. Rémy Morgan: Hi, I’m Remy, I’m an astronomy student at CU Boulder with Collin and Tara and I work as planetarium as a presenter usually

Tara Tomlinson: Awesome. And I hear you have some cool black hole news to share with us. Rémy Morgan: Boy do I so you know as a news anchor. I have made it my mission to track down, you guessed it anchors, but also news and I just so happened to have some about the topic at hand, Rémy Morgan: which is supermassive black holes which is such a coincidence. I know. Rémy Morgan: So Word on the street is that some compact objects like neutron stars or stellar mass black holes have heard beats. Rémy Morgan: Not from pumping blood, but from eating material is called a quasi periodic oscillations. Say that three times fast. And it happens when a black hole has an accretion desk is eating stuff like you can see behind me. Rémy Morgan: So the intensity of say x ray emissions ends up with a bit of a beat to it a particular frequency, a fairly regular amount of time between peaks and output. Rémy Morgan: It’s not terribly uncommon event. It’s interesting and can tell astronomers a lot about like what sort of system you’re looking at kind of give an idea of the mass of an object, but it’s not really a miraculous find in the long run. Rémy Morgan: But why is this news rainy you ask.

Rémy Morgan: Well, dear listener. What makes it news takes a bit of digging.Firstly, this sort of event is extremely uncommon in supermassive black holes. The ones at the center of galaxies like you’ve been talking about. Rémy Morgan: So smaller black holes you know that tracks, but even the most extremely energetic active galactic nuclei don’t often have these oscillations. These heartbeats. Rémy Morgan: So the number of, you know, galaxies that have this can be counted on your fingers, which isn’t much compared to the number of active galactic nuclei that we know of and have observed. So that’s know worthy. Make note. Rémy Morgan: The reason it’s news and not notes, however, is because there’s a pretty neat case that they very recently published some data on. Rémy Morgan: So the first first galaxy to have these quasi periodic oscillations or QPO measured is called REJ1034+396 which is catchy.

Rémy Morgan: So REJ10, REJ. It’s “REJ” for the moment wretches QPO was first identified back in 2007. The x ray oscillations were on the scale, about an hour and again pretty unexpected. Rémy Morgan: So they continued observing this galaxy for a few years until that pesky Sun caused some troubles preventing proper observations from 2011 all the way through 2018. Rémy Morgan: Data were taken again, finally, in 2018 and the results were published just last month. And it turns out that oscillation is still going strong. That’s a pretty long time to have such a regular heartbeat. Rémy Morgan: So generally, QPOs are a byproduct of those feasting compact objects, but to have such a regular pulse for such a long time for such a large black hole, this one a few million times the mass of the sun. It’s pretty exciting.

Rémy Morgan: So according to Professor Chris Done at Durham University these pulses are likely indicative of maybe change in size or shape of its accretion disk, expanding and contracting. Rémy Morgan: So this sort of behavior has really been seeing a stellar maps black hole feeding off a companion star. So black holes on the scales of like 100,000 times smaller than this one. Rémy Morgan: Though no particular cause has been identified and confirmed as of yet they’re looking into it with anticipation. The papers lead author Dr Chichuan Jin, Rémy Morgan: who rightfully calls the heartbeat “amazing”, believes that this will provide the best opportunity for scientists to further investigate the nature and origin of this heartbeat signal. Rémy Morgan: So next on the to do list is to keep up with the analysis and do some comparisons with those similar behaving stellar mass black holes, which means it’s a DEVELOPING STORY. An active mistery. So keep your finger on this black holes pulse, because it’s got plenty to tell us Tara Tomlinson: Fabulous, really, really cool.

Rémy Morgan: Definitely is. Collin Sinclair: Okay, a cool. Wow. That’s, yeah. I had no idea that black holes had heartbeats. Collin Sinclair: I didn’t know that Collin Sinclair: for even stellar mass black holes. Collin Sinclair: Thank you for for putting that research together and sharing this with us. Rémy Morgan: Absolutely. Tara Tomlinson: So, our first guest for today is Jimmy Negus. Tara Tomlinson: This is excerpts from a recording we did a couple weeks ago. Tara Tomlinson: So, hope you guys enjoy our chat with Jimmy. Collin Sinclair: And today we are going to be joined by Jimmy Negus who is a PhD candidate at CU Boulder studying active galactic nuclei or referred to as AGN. Collin Sinclair: With the Sloan Digital Sky Survey or SDSS. Which is a telescope survey. And with this survey, he can analyze the light from 10,000 galaxies to identify signatures of movement and composition in their bright centers. So Jimmy, did you want to add anything to that or correct anything? James Negus: I think that was a beautiful explanation I you know I obviously think AGN are James Negus: the best objects in the universe. Collin Sinclair: “The best!” James Negus: And I look forward to discussing more about, you know, sort of our attempts to understand their nature and their impact on galactic evolution. Tara Tomlinson: That is very cool.

Tara Tomlinson: I love how you put it on your website. I love this sentence that you wrote out that says “at the core of each galaxy, there exists a supermassive black hole, a dense cosmic region with a mass equivalent of up to a billion solar masses.” That’s just so poetic. Tara Tomlinson: I like how you put that. Tara Tomlinson: Just to clarify, so do most scientists now think that every galaxy has a black hole of the center? James Negus: Every massive galaxy. James Negus: So the exception of course you have dwarf galaxies or irregular galaxies. James Negus: So you can think of objects like the Small Magellanic Clouds, the Large Magellanic Clouds. James Negus: For objects like those. It has not been confirmed that at the center of all of those entities, there exists a black hole. James Negus: But what has shown in the literature, with very, very strong consistency and evidence is that supermassive black holes do occupy these inner regions. James Negus: And, you know, of course it’s astronomy, so we can only provide the strongest consensus. James Negus: It’s, it’s always it’s a scientific process. So it’s always under constant review and evaluation. And so that’s why we, you know, nothing is 100% definitive but we strongly believe that this is the case for our massive galaxies in our universe. Tara Tomlinson: Okay, cool. I like that, because you know it’s one of my favorite things to tell people is that black holes are not like this rare exotic thing. Tara Tomlinson: They’re kind of everywhere.

James Negus: There are many to be believed to exist in our, in our own galaxy just at a much smaller scale than the supermassive ones. James Negus: And when I say supermassive. What I mean is: James Negus: by a million or more solar masses. The equivalent of a black hole is mass. Once you’ve reached that threshold, you are then considered supermassive. Tara Tomlinson: Let’s bring it a little closer to your research. You specifically look at active galactic nuclei. The center of galaxies. So how is an AGN different than a black hole, specifically? James Negus: Indeed, indeed. James Negus: So an AGN is where things – It’s no holds barred – it’s where things get very interesting. James Negus: And what we have is usually most galaxies host quiescent or quiet black holes, so they exist at the center of these galaxies, and matter James Negus: you know tends to orbit around them, but they don’t cause too many problems. James Negus: However, if you have perturbations or disturbances or things become uncomfortable for that black hole…. So you can think if, say, a merger is underway, or if you have James Negus: collisions of of massive compact objects…. If you have turbulent events, what can happen is this supermassive black hole can begin to accrete matter violently around this black hole.

James Negus: And for about 10% of the cases we believe that very powerful electromagnetic radio jets can stream from James Negus: the axis perpendicular to the plane of the galaxy. And so what we’re seeing in these active galactic nuclei is essentially particles that follow strong magnetic field lines. James Negus: But to answer your question directly, an active galactic nuclei is when active accretion which is just the rapid funneling and spilling of matter directly James Negus: Onto the sphere of that black hole. Once that begins, we consider that galaxy active and for reference, our own black hole Sagittarius A star. James Negus: Is acquiescent galaxy. So we believe that it is not active, but it’s not to say that it cannot become active or that it was active at some point in its lifetime. Tara Tomlinson: Okay. So, and that’s another question that I get all the time with, you know, we hear about these bursts and these radio jets and things if these black holes are so dense and have so much gravity that like not even like can escape this, how is this huge jet of radio Tara Tomlinson: coming out of it?

James Negus: Of course, of course. So we have entirely different processes that at effect. And so the gravitational force is actually one of the weakest forces in our universe. James Negus: And what is stronger than that are electromagnetic forces. And so what happens is you’re having particles dust gas you have stars, James Negus: baryonic matter, that is is funneling around this black hole. But these are all electrically charged particles and states of matter. James Negus: And what happens is when you rotate these electrically charged particles you create magnetic field lines perpendicular James Negus: And this is actually much stronger than the gravitational force that’s trying to pull the matter in. And so what you’re having is is is an interplay between James Negus: This matter and the magnetic field lines. That’s overcoming the force of gravity and these are actually some of the most powerful signatures of the universe that are usually observed an X ray James Negus: And have velocities that can approach fractions of the speed of light. So these are very, very energetic and powerful.

James Negus: Radiation that we’re we’re observing Tara Tomlinson: Yeah, but for now we can study these the specter of the light than the energy that’s, you know, around that black hole and coming out of the AGNs, which is what you do, you look at the go light Tara Tomlinson: This reflecting off of their being admitted out of there. And so what kind of things can we learn from the spectra of these Ag and James Negus: Indeed, indeed, so spectroscopy isn’t astronomers best friend, you know, unlike many sciences physical sciences. James Negus: On Earth, you know, we can’t just go to a laboratory and measure James Negus: Measure properties we want. So we have to rely upon our observations and of course these objects are extremely far and we can’t just send a probe to a black hole. James Negus: So our best friend is how can we analyze the light that is emanating or produced by these objects. And through spectroscopy, we can attempt to gain some understanding about the fundamental physics of what we’re seeing and James Negus: in particular AGN are known for the extremely fast cloud velocities that orbit their black holes.

James Negus: And so the first sort of telltale sign that you’re viewing an AGN, particularly if you’re looking at it pole on James Negus: His will notice very, very broad emission lines and broad emission lines correspond to the velocity of the matter that’s orbiting these black holes. James Negus: Or that’s being ejected from these black holes. So one of our best friends is studying a lot of the spectral lines and for my project in particular I’m looking at the ionization states. So when an atom becomes ionized or effectively stripping an electron James Negus: And to in order to strip electrons from certain species of matter. James Negus: It requires abundant supplies of energy and we believe that there are certain highly ionized species that unambiguously correspond to active galactic nuclei. James Negus: And so my project is can we hunt down these ionized gas signatures, so that we can better find these AGN James Negus: And that is the true challenge is finding the age again because we would love to study them, we’d love to learn the properties, but we’re learning that it’s hard to James Negus: Hard to find these AGN, you know, in some cases, there’s not enough light that’s being emitted for us to detect and so similar to black holes that are quiet. We try to infer the presence, based on the response of the matter around it.

James Negus: And so my project is really getting at the heart of understanding the behavior of the matter that he and are interacting with Tara Tomlinson: So even though these things are, you know, super active and bright and fast everything are still difficult to find. James Negus: So a caveat here is, they’re very bright and they’re very active. But what we have is other processes that can mimic AGN James Negus: So they’re very bright. But imagine if you had an James Negus: AGN that is millions of light years away. James Negus: And let’s say you had a supernova, you know. So what happens is you can have supernova remnants that mimic James Negus: These AGN signatures because they’re also very bright powerful events and given the distance. Sometimes it’s hard to infer which one is which. James Negus: And most of our advances in the field of AGN study rely upon the ratios of prominent emission lines to determine this. If it’s an AGN or not. James Negus: And this is due to the energies, like I said, that are required to produce certain lines. The problem with that is, again, you can have star formation contaminate. A lot of these ionization ratios.

James Negus: Because fast out flowing energetic processes tend to mimic each other and so it can be very challenging and and this was actually the foundation so AGN James Negus: are called quasars, which the root of that is quasi stellar object. And that was because we didn’t know if they were just very bright stars or if they were actually what we know today as active galaxies. James Negus: So it’s a very challenging field but spectroscopy is is an astronomers most valuable asset in terms of peering through the night and and really resolving some of the mysteries of the universe. Tara Tomlinson: Yeah, it’s, it’s definitely my favorite thing Tara Tomlinson: to tell peole all the time. Tara Tomlinson: Yeah, just it’s I think it’s crazy that just by seeing the different ways that light. Tara Tomlinson: Can be emitted from something, you know, hundreds of millions of light years away, like if you look at it until if that’s grass or astroturf you know it’s James Negus: it’s crazy it’s crazy. James Negus: It really is fascinating.

Tara Tomlinson: Awesome. Well, I’m gonna pass it back over to Collin and he’s gonna ask you some more personal, but just more questions about you as a scientist James Negus: Of course, of course. Collin Sinclair: So, so, yeah, it’s just that I’m going to kind of we’re gonna, I like to always go back in, in, you know, it’s fun to kind of learn about the the backstory is and kind of your personal story. How did you get to where you are working on all this cool stuff. Collin Sinclair: That’s my question for you. Did you always want AGNs or black holes or astronomy in general or James Negus: Yeah! Collin Sinclair: About yourself. James Negus: Indeed, so, um, this truly started in in 11th grade for me where I built my first Dobsonian and telescope and you know I really just knew I had a broad interest in astronomy. I wanted to study the stars. I wanted to learn more about our origins and and the greater context for how our universe. James Negus: Is woven together, you know, what are the fundamental laws dictating it. James Negus: I wanted to see what the true extent of our backyard was and this motivated me through college to study physics. I knew I had to get the fundamental understanding of the physics and math.

James Negus: And a lot of students I have, you know, they begin to astronomy and they just want to see pretty pictures and that certainly is a part of it. But the fundamental underpinning of that is understanding the physics and the math. James Negus: And so I went to University of Chicago, and I got my degree in physics with a specialization in astrophysics, and my interest were still pretty broad James Negus: And I actually after undergrad took a few years off and I studied actually assumed position doing engineering at a company in Boulder, Colorado. James Negus: Working with atmosphere. Atmospheric profiling right it’s it’s you know it’s it’s small scale astronomy, it’s, it’s very local. James Negus: But I knew after a few years, that my true interest was returning to the cosmos and, in particular, a thing that fascinated me was high energy astrophysics. James Negus: And the root of this interest is the influence high energy astrophysics can literally change the very basis of a galaxy, it can it can alter. It’s very evolution.

James Negus: And so everything that stems from that evolution from planetary science to astro-chemistry to astrobiology are all to me, symptoms of the high energy processes that determine the structures and their behavior. James Negus: And so to get to the root of high energy processes. What better than AGN, you know, these are some of the most powerful objects. Some of the most distant objects. James Negus: That power. A lot of the galaxies that we observed. And so for me, it was really just wanting to understand more of that. And the process was James Negus: Working closely with my advisor and discovering I really loved observational astronomy, I really loved not only understanding the physics, but seeing, seeing, you know, the objects that James Negus: Were compelling me so and so really observational astronomy and AGN sort of found me. And, you know, as I understand, more and more about AGN James Negus: The more I learned about you know everything about astronomy and astrophysics. It really has a huge expansive trickle down effect. And it’s been a pleasure to see how it connects and how that web James Negus: Really links to other other events in the universe.

Tara Tomlinson: Yeah, so now we’re going to transition into our Tara Tomlinson: questions from the public segment we’re calling this CAPCOM. Tara Tomlinson: People are reaching out to us and we’re releasing their messages to our expert. Tara Tomlinson: So we’ve got some questions from the public that we’re going to throw at you see what you think. Tara Tomlinson: So the first one is from Mic in Boulder. He wants to know, what’s the tiniest black hole we know of? And do we Tara Tomlinson: Still think Tara Tomlinson: micro black holes exists? James Negus: Alright, so the tiniest black hole. James Negus: Is on the order of a few solar masses. And so these are James Negus: Black holes that can arise from the stellar evolution process. So they are very tiny. James Negus: But they’re nothing compared to micro black holes which are still from what I understand, theoretical objects. And so I’m not sure if many of you are familiar but CERN, there were concerns about, you know, are they going to create a black hole and destroy the earth. James Negus: And so let’s think about the most famous equation E equals MC squared (E=mc^2). And so if we’re talking about James Negus: A black hole. We’re talking about a dense concentration of mass which is equivalent to a high abundance of energy. So mass and energy are essentially equivalent James Negus: And so you could consider if we had a very energetic process, such as two particles smashing into each other could recreate a micro black hole and the theoretical minimum size of such a black hole is known as the James Negus: Sort of the Plank mass would be the massive such an object. And that’s about the massive a flea egg for reference.

James Negus: And these are purely theoretical and it has long been suspected that we don’t even have the energy capabilities to create such an object. And if through some crazy act we did it will survive for tend to the negative 24 of a second. James Negus: So it would be extremely, it would evaporate instantaneously. In essence, because its massive so small and it could not sustain itself. So what essentially evaporate almost immediately. Collin Sinclair: So, Tara Tomlinson: I go back, sorry. Go ahead. Tara Tomlinson: What I was going to say, and kind of going back to what we talked about earlier black holes are not like these infinitely sucking things. There’s only so much that it can do. And if it’s exactly we’re probably not in any danger. James Negus: Exactly. So we’re safe for now, folks. Tara Tomlinson: Excellent. Collin Sinclair: For now, James Negus: For now.

Collin Sinclair: Jimmy your response to that question actually leads perfectly into our next question, which comes from Vince in New York State Vince asks, you know. All I know about Hawking radiation is that Collin Sinclair: Black holes evaporate. And so the first question is, if nothing can escape through a black hole, then how can they evaporate if that if that information is destroyed?Then you know how, how can kind of come back in that way. And second of all, Collin Sinclair: If they can evaporate and if the black hole we “saw” Collin Sinclair: Recently M87 is is 53 million light years away. Is it possible that it’s gone by now, at this point in space because what we’re seeing is Collin Sinclair: million years old? James Negus: Excellent. These are great questions. And so, Hawking. James Negus: Was a great scientists who study by calls and he you folks, the theory of Hawking radiation. And so essentially there is quantum law quantum law called quantum unitarity James Negus: And essentially what that means, what the law dictates is that no information in the universe can just be lost, it must be accounted for, or traced in some form. James Negus: So as we’re all familiar with energy is conserved. So if something disappears, that the logic is that energy is somehow just transmuted to assume a different state.

James Negus: And so that is sort of the fundamental backdrop for Hawking radiation. And so, Hawking radiation to resolve the information that is “lost” in a black hole. James Negus: posits that as a particle enters a black hole in his last forever to preserve the signature of that particle, there is an anti particle James Negus: That is emitted in an opposite direction. So, one goes in as last one comes out an antiparticle James Negus: And the theory is at Hawking radiation is it accounts for this radiation that to an observer would seem to be lost from a black hole and over long enough timescales, that the equation suggest that if a black hole can actually evaporate over long enough time scales. James Negus: Hello. However, the theory also suggests that the order is longer than the time of the universe for a black a typical black hole to evaporate. So again, we’re talking about billions and billions and billions of years to theoretically evaporate any sort of moderate or massive black hole. James Negus: So yeah, no, it’s very, it’s very certain that that black hole did not evaporate. James Negus: On the time scales. What is far more likely would be, say, a James Negus: Merger or if the AGN turned off or turned on. These are much more reasonable on on our cosmological timelines.

Collin Sinclair: So when we talk about the little micro black holes that we were discussing from that first question, you mentioned that you know it would almost instantaneously evaporate. Is that through the same process of Hawking radiation or is that something else going on there. James Negus: So my understanding is, those are just inherently unstable processes, it’s, it’s not massive enough to really sustain itself in the first place. So I’m not an expert on on micro black holes I studied the big guys James Negus: But my theory is that they are too disconnected processes and it’s more of a stability issue because we’re creating energy James Negus: Almost instantaneously. And that black hole just cannot sustain itself long enough. Collin Sinclair: Got it, thank you. James Negus:No problem. Tara Tomlinson: So I think we talked about this next one a little bit, but I’ll throw it out there again because Ray in Austin wants to know about the distortion of Space Time. Tara Tomlinson: And how does that affect the motion of other kind of cosmic bodies moving around the vicinity of like you mentioned, this trampoline with the huge the huge dip in it. Do we we directly see that sort of motion happening? James Negus: Indeed, indeed, and it’s most traceable by simply looking at light so light is obviously, you know, it’s how astronomers view of the universe. And so what we’ve noticed is through gravitational lensing.

James Negus: If we have distant stars and galaxies that are emitting light and there’s a black hole in between us and those sources will notice that the light itself becomes distorted. James Negus: And that is a property of the black hole, its gravitational influence is literally bending that light. James Negus: And in similar processes through gravitational effects you obviously have stars that are tidally disrupted and rupture and fantastic explosions as James Negus: As the star as part of the star is is is pulled towards the black hole, it becomes shredded, in a sense, and so you can have funnels of matter that are also that also result from black holes pulling on neighboring matter. James Negus: So these are very, very intriguing objects, you know, very intriguing objects and and that is, in fact, how we know they exist is through their distortion and their effect on matter, that is that is how we we infer that they they are our companions, you know, in the universe. Tara Tomlinson: Alright, well thank you so much for joining us JImmy. Jimmy Negus our grad student from CU Boulder awesome to have you on the show and Tara Tomlinson: If anybody has any other black hole questions they get submitted, we might contact you a little bit later and see if we can get an email response. Otherwise, yeah. Thanks again for coming in and chatting with us. It was really fun. James Negus: It’s been a pleasure to be on board. Thank you very much for having me. Tara Tomlinson: Alright, thank Jimmy. Collin Sinclair: Thanks, Jimmy.

Tara Tomlinson: Alright everybody, I am super excited to introduce our next guest, Dr. Andrew Hamilton. He’s a professor of astrophysics here at CU Boulder is also a fellow at the Institute for laboratory astrophysics. Tara Tomlinson: He’s got interest in relativity and cosmology and of course black holes. Tara Tomlinson: Dr. Hamilton was also a contributor to the planetarium film “black holes.The other side of infinity” which we show here at Fiske and it shows at planetariums all across the country.So we are super excited to talk to you today, Dr. Hamilton. Dr Hamilton: It’s a great pleasure, Tara. Thank you very much. Tara Tomlinson: Thanks for joining us. Collin Sinclair: So I’d like to kick things off with what to us, seems like a very simple question, but it’s perhaps the most important question of the episode and this is coming from all sorts of listeners, and the question is:”What is a black hole?” Dr Hamilton: A black hole is a place where space is falling faster than the speed of light. That’s it.

Collin Sinclair: So concise so straightforward. You said it’s where space is is falling faster than the speed of light. That’s right. Dr Hamilton: People often say a black hole is a place where gravity is so strong that not even like can escape. Dr Hamilton: But that leaves. Again, why can’t light escaped from a black hole. The answer is a simple one space itself is falling faster than light inside the horizon of a black hole, and that’s why light cannot get out Dr Hamilton: You may have heard, perhaps, that nothing goes can go faster than the speed of light. Dr Hamilton: The trick is nothing can go through space faster than the speed of light that space itself in Einstein’s general relativity can pretty well do what it likes including pieces of space time being able to depart from each other, faster than the speed of light. Tara Tomlinson: I’ve never heard it explaned that way, that’s great. Collin Sinclair: That is very, very cool. I haven’t. Yeah. That is awesome. So there we go. Dr Hamilton: Let me give you a little bit of attribute here. It wasn’t me. Who came up with this idea of space falling faster than the speed of light. Dr Hamilton: It was come up with by two gentlemen. One, Allvar Aullstrandand the other Paul Painlevé 1921 Dr Hamilton: What they did was a piece of mathematics. Curious enough, hey didn’t understand the mathematics. And that’s very common in the field of general relativity Dr Hamilton: But nevertheless, they showed, even though they didn’t understand in that space phones faster than light inside the horizon of a black hole.

Dr Hamilton: Allvar Aullstrandand was a Nobel Prize winner. He won the Nobel Prize in 1921 for his work on the optics of the human eye. And he was on the Nobel Prize committee that in 1921 prevented Einstein from winning the Nobel Prize for relativity Dr Hamilton: They awarded it to Einstein, not for relativity, but for the photoelectric effect. Dr Hamilton: And Paul Painlevé is equally interesting because he was Prime Minister of France on two occasion for a short amount of time before 1921 and after 1921. So it was an interesting set of folks. Tara Tomlinson: Sounds like. That’s very cool. Collin Sinclair: Yeah, and I think it’s it’s really nice to incorporate these kind of historical stories into the science that makes it a lot more interesting. Collin Sinclair: You said something that actually leads perfectly into another question that we have for you, which is that Collin Sinclair: You’ve said, as Dr. Andrew Hamilton that to understand black hole theory: “You just have to trust the math.” Collin Sinclair: And on the surface, the mathematics in the papers that you’ve written and in countless others, doesn’t look too crazy advanced beyond an undergraduate mathematics education.So what is it about the math and the equations that is or seems so challenging to trust it. Dr Hamilton: So first of all, Dr Hamilton: Even though astronomers see evidence for things that look very much like black holes stellar size black holes and supermassive black holes of the centers of galaxies, even though astronomers see these things.

Dr Hamilton: We can’t go inside, so we can’t test them. Dr Hamilton: And so in order to understand what these things are black holes. We have to understand the mathematics. We have to understand the physics we have to turn that handle Dr Hamilton: And a priori, one doesn’t know what you’re going to get. You don’t know what you’re going to get before you do the mathematics. I got into studying black holes through visualization. I didn’t start off with thinking black holes are called as a research project I thought Dr Hamilton: What happened was I wanted to teach relativity to undergraduates and for some strange reason which escaped me undergraduate seemed to be fascinated by black holes. Dr Hamilton: And so it was undergraduates and teaching that got me into this role of doing visualizations of black holes and, in particular, visualizing what happens when you fall inside the horizon of a black hole. Dr Hamilton: Which hadn’t been done before. Dr Hamilton: And it’s very interesting because Dr Hamilton: I didn’t know what it would look like I did the mathematics that Dr Hamilton: The equations of general relativity are quite specific. So you knew what equations to solve and you knew how to do the ray tracing, but you didn’t know what it would look like. And then when you did those visualizations. They wouldn’t look at all like I expected.

Dr Hamilton: And in my experience that is quite typical in general relativity, you do a calculation and you have a preconception of what it should look like. Dr Hamilton: And that preconception isn’t borne out by the actual mathematical calculations you do Dr Hamilton: So if you find yourself sometimes baffled by black holes and possibly baffled by the mathematics of black holes. Welcome to the club. Dr Hamilton: Because I’m the first person to admit and constantly baffled. It doesn’t stop me doing the calculations and eventually slowly figuring out what those mathematical calculations mean. But beforehand? No, I have a success rate of zero percent on anticipating, what’s the right answer. Tara Tomlinson: Fair enough. Dr Hamilton: I should say I have become more interested Dr Hamilton: In high energy physics and theories, then, of everything in the last few years because it does seem that in order to understand what’s happening inside black holes in particular in this extraordinary region near the inner horizon. Dr Hamilton: where things get bang together a Big Bang energies to understand the physics of what’s happening there. I need to understand high energy physics and possibly theories of everything. Tara Tomlinson: And that kind of perfectly leads into my next question is, as someone who you know lives and breathes in this field, where do you see the black hole research sort of going or where do you hope that research is going your future. Dr Hamilton: I’m going to speak.

Dr Hamilton: For myself, personally. Dr Hamilton: There is a substantial community of astronomers who do real work. Dr Hamilton: Real black holes observing black holes, one way or another with various telescopes optical x ray radio nowadays, you’ve heard about The Event Horizon Telescope. Dr Hamilton: Gravitational waves being detected from mergers of black holes all good real astrophysicist, I find myself a little bit lonely in trying to study what happens inside black holes. Dr Hamilton: My excuse is is that I didn’t want to get wonderful inside a black hole, but because I was doing visualizations and taking people through the horizon of black hole and trying to figure out what happened. Dr Hamilton: My research basically got preempted, and has forced me into that area. And I’m very thankful, because it’s a fascinating area. Dr Hamilton: But I would love to see more Dr Hamilton: Scientists interested in black holes I sometimes hear from my colleague, I sometimes hear from my colleagues that is astronomy of black hole stops at the horizon, because you can’t see beyond the horizon. Dr Hamilton: And there’s something to be said for that idea, but on the other hand, what happens inside, inside black holes is to me the most interesting question. Dr Hamilton: In all of physics and could potentially lead to an understanding of such things of how our universe was made, how baby universes might be made. Dr Hamilton: Is there a multiverse. What are the laws of physics at very high energies. I think these are fascinating questions which can be answered in a more practical way than just sitting down and trying to dream up new ideas. Nature is already giving us clues with black holes. Tara Tomlinson: Um, and in working with, you know, kids and adults public audiences that sort of thing,do you ever find there’s any really sort of common misconceptions that you end up clarifying a lot or things that you especially like to harp on? Dr Hamilton: The world of black holes is I’m sad to Dr Hamilton: say packed with misconceptions.

Dr Hamilton: Deary me. These statements that are made, often by my colleagues and often repeated in the popular literature. Dr Hamilton: And here I am saying that these are misconceptions. Why? based on my own authority. Why do I say that because Dr Hamilton: I’ve done the calculations and I did the calculations expecting to get the standard result. And lo and behold, they didn’t agree with what people say. Dr Hamilton: And you’ve got to believe that mathematics. So eventually, you say, oh, okay. I have to revise my thinking here. Let me give you Dr Hamilton: Probably the most classic example is a statement that is very commonly made the black hole is a place where matter get compressed gets compressed to an infinitesimal point called the singularity at the center of a black hole. Dr Hamilton: That is wrong. Dr Hamilton: Would you like me to list of famous people who have stated that Dr Hamilton: Would you like me to list of famous people who have stated that Dr Hamilton: Nevermind. There’s, there’s a whole bunch of people who say that the singularity of a black hole is a point where all the matter that is accreted into the black hole concentrates into an infinitesimal point of infinitesimal density Dr Hamilton: Here’s the problem. Dr Hamilton: If you fall into a black hole. Imagine two people falling into a black hole. Dr Hamilton: And it’s a spherical black hole. Let’s make it that way, non spinning so it has something called the singularity of what appears to be a center. So these two people try to fall in and they try to fall in at the same time.

Dr Hamilton: The question is, do they meet the answer is they don’t Dr Hamilton: Because inside a black hole space is falling faster than the speed of light. So if you’re inside a black hole, whichever direction you’re looking at. You’re looking always looking at outside your position. Dr Hamilton: Let me take you through this a little bit more carefully. Dr Hamilton: So people ask this question. For example, suppose I fall feet first through the horizon of a black hole. Dr Hamilton: What happens? Dr Hamilton: So you’re going to be freely falling, you’re not going to be fighting it. You’re going to be free falling and so your feet fall through the horizon of the black hole Dr Hamilton: At the moment, your feet fall through the horizon, your eyes are outside. So they you’re looking down at your feet, your feet are below. Dr Hamilton: Your feet emit light and because space is falling at the speed of light that the horizon, the light that your feet in it sits there and the horizon barreling away at the speed of light through spaces for speed of light. Meanwhile, your head comes down. Dr Hamilton: And catches up with a light from your feet. Dr Hamilton: And the question is, do you catch up with your feet? No, you don’t. You look down. You still fee see your feet below you. And if you continue to fall inside the black hole. Dr Hamilton: You look down, you still see your feet below you. But you see an image of your feet as they used to be above your head. Dr Hamilton: Yes, your feet inside the black hole, your feet emmit like upwards, but because faces falling faster than the speed of light it drags of the light downwards, like a Michael Jackson moonwalk and your eyes eventually catch up with that.

Dr Hamilton: I want to do a little aside here and you can edit this. Dr Hamilton: This is something that it seems the community doesn’t understand very well in, particularly with regard for example to Hawking radiation and quantum gravity. Dr Hamilton: Hawking radiation, Hawking told us as admitted that horizon of a black hole, and it seems like many physicists, imagine that when you fall to the horizon of a black hole, you will catch up. Dr Hamilton: With a Hawking radiation. Well, no, you don’t catch up with a Hawking radiation, you don’t catch up with a light from your feet and you don’t catch up with a quantum radiation called Hawking radiation. Dr Hamilton: So there’s some deep misconceptions about the nature of of the horizon amongst the quantum gravity community. Dr Hamilton: Back to where I was that you can just cut all it was to to advance. Where were we. Yeah. Dr Hamilton: So, Dr Hamilton: The light that’s emitted inside that a black hole has to be falling in words and Dr Hamilton: In order for light for me to be able to Dr Hamilton: I really want to show you a picture. Am I allowed to show you an image instead. This is getting too complicated. Collin Sinclair: You can. The trick is that we expect a large portion of the listeners to be listening audio only so they will not get the experience of looking at the picture.

Collin Sinclair: And if we’re over our heads. That’s okay, we can kind of Collin Sinclair: Back out of this knowledge. Right. Dr Hamilton: Let me see if I can summarize what’s really going on. So you’ve got two people who are falling in at the same time or train these trying to Dr Hamilton: But because of this strange business of space falling faster than the speed of light. Dr Hamilton: And I can imagine I’m one of those infallers none looking and trying to look at this other person here, but because space is falling faster than the speed of light. I’m actually seeing stuff from outside of me. Dr Hamilton: And if I try and connect my light rays to the other person. I find that they connect only when the observer as well away from the horizon. Sorry, well away from the singularity. Dr Hamilton: So the net result is, I not only do not collide with this other person of the center but I lose causal contact with this other person already well away. Dr Hamilton: From the singularity of the black hole. And if we lose causal of contact. That means that when we fall to the singularity for to too causely separated pieces of Space Time. So the right way to think about the singularity is it’s actually a surface. Dr Hamilton: When people fall along different anger positions they fall to a different point on that surface the singularity of a black hole is a surface and not a point Dr Hamilton: If you want to understand Dr Hamilton: What that surface is you do have to go beyond Dr Hamilton: General Relativity, you have to understand quantum gravity, but within the context of general relativity, you can say without Dr Hamilton: Any doubt the singularity is a surface and not a point Collin Sinclair: Thank you again so much for, for being here. It’s been a pleasure to have you. Dr Hamilton: Absolutely. Thanks for all the work that you’re doing for Fiske it’s so fantastic to see you guys doing that. And I must say I’m terribly impressed, not just with you, but the rest of the Fiske staff. Dr Hamilton: And with the Fiske director John Keller, who, as far as I’m able to see is doing an absolutely fantastic job of keeping Fiske floating and thriving in these difficult times, and getting all of you guys functioning in the best possible way. So thank to to you All Tara Tomlinson: Alright folks, that our episode for today.

Thank you so much again to our guests Jimmy Negus and Dr. Andrew Hamilton. Tara Tomlinson: Now these are just excerpts of these interviews. We will air the extended interviews, with the full information.Those are going to be avalible on our YouTube and on SoundCloud. Tara Tomlinson: Now, come back next week for sure, because we’re going to be talking about Mars! Tara Tomlinson: We’re going to have Andrew Wilkoski, another grad student here at CU, as well as Dr. Dave Brain.

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