字幕表 動画を再生する 英語字幕をプリント Hello and welcome to dark frontiers a conversation about the science of black holes thanks for tuning in i'm lee billings an editor covering space and physics at scientific american and our guest today is Dr. Priya Nadarajan an astrophysicist at Yale university and author of mapping the heavens Hi Priya hi hi everyone now priya is very interested in what we might call the dark side of the universe and i'm not talking about sith versus jedi here i'm talking about all the mysterious things that lurk out there unseen dark matter dark energy and oh yeah black holes so priya again thank you for being here today now before we really get into it i want to do a minor bit of housekeeping for everyone watching uh if anyone in our live audience has trouble hearing or seeing the discussion uh please use the chat function to let us know my colleagues jeff delicio uh sonia buddha and macarena carazosa are standing by to assist you and if you have questions for me or for priya remember this is going to be a q a at the end you can submit them to the organizers using the questions panel in your go to webinar menu we're going to answer as many as we can during that q a session at the end of our conversation and you know speaking of audience participation jeff if we could go ahead and advance the slides one uh we're gonna kick things off with our first poll that's right pop quiz guys um this is one of three that we're going to be doing throughout the presentation uh the first question here you can see is how massive can a black hole become how massive can a black hole become you're going to have about 30 seconds once this kicks in uh and there will be multiple choices and then we're going to read them out we're going to have priya talk about it really quickly they're going to get into the meat so let's go ahead and have this first poll folks we're going to see what happened paul results we have i think everyone maybe can see this but i'll read it out loud hey as massive as hundreds as 100 stars we have four percent saying that b as massive as millions of stars six percent said that see as massive as several billions of stars that's a lot of stars 25 a quarter of you said that and d said no limit black holes can grow indefinitely 65 percent of you said that now priya let's go to the experts priya i want to know which answer is right right lee do you want to take a shot first so i thought the answer was d black holes can grow indefinitely that's kind of what i thought but you know i i've kind of cheated i had a little bit of behind the scenes uh coaching on this apparently priya that's that's not the right answer it's not the right answer okay so in fact um it turns out you know um we did some work about 10 years ago where we showed that from what we understand so far about black holes they actually kind of limit their own masses so they start their own growth eventually so we believe that they can grow up to several billions of solar masses but then eventually stunt their own growth so they don't grow indefinitely because you know they are locked in into the host galaxies that they're sitting in and so it's the interplay of the available gas and what's going on in their larger environment and what they actually do black holes do to impact the environment that they're sort of unnaturally they stunt their growth so a galaxy of a given size ends up having an optimal size black hole and so it doesn't grow indefinitely okay okay i'm trying to imagine some kind of weird scenario where there's you know a big galaxy cluster with hundreds of thousands of galaxies and somehow they all just glommed together and then it all feeds one big central one but but maybe we'll get to that later whether or not that's feasible because we first do that later because what i want to get to right now is actually the first section of our talk we could have the next slide please um we started out just the basics how black holes became real and i want to start really quickly with an anecdote for you priya this is actually based on a real life experience of mine a real friend of mine every single time we get together she knows i'm a science writer and she always has the same question for me which is lee why does anyone think black holes are real they're too ridiculous to exist it's impossible how could they be real they're too radical to exist and i want to i want to raise that because this is actually not that crazy of a question in fact as i understand it and i'd love to hear more from you about this einstein einstein who's whose theories of general relativity and special relativity really inform the basis of understanding of black holes at a fundamental level famously he used his intuition for all kinds of things he imagined he would ride on a beam of light or uh ride in a windowless elevator he had these thought experiments that he would do to to help his thinking about the universe um and through his intuition he would come to these great conclusions yet even so he did not believe that black holes were real when they kind of popped out his equations right so so how is that true that is true so einstein was really quite an intriguing person like and he was a real sort of hold out when he came up with the most radical theories that completely transformed our understanding of the universe right the fact that um you could describe the entire universe on his contents and so on his general theory of relativity reworking gravity um but when the implications of his theories were worked out he often didn't like the implication like he didn't i like the idea of an expanding universe it was a natural consequence of Einstein's field equations right he didn't like that why because he was you know emotionally attached to the idea of fixity of a steady universe it was very disorienting to think of the universe as expanding right likewise the reason he didn't like black holes first of all he never expected so the black hole solution which is the gravity of a very compact mass how intense it is and how it deforms the space around it is an exact solution it's a simple exact solution to his very complex equations he never imagined there would be a simple solution so that was a surprise but then it was what this solution was that he didn't like so this solution as we'll see later on there are many different ways of thinking about a black hole n cases what is called a singularity so it's a place where all the known laws of physics break down and he did not like that he said oh that's really perverse and um so again it's sort of aesthetic reasons almost that he didn't like it but you know eventually he sort of got around but i think what is more interesting about black holes right um you know coming back to your friend you know is oxygen not real just because we can't see it that's not the case right i mean there are lots of entities that we are happy to believe they exist whom whose existence we infer only indirectly so you know black holes we infer their presence indirectly as with dark matter for example right so there are lots of entities um that we are used to in life there uh but you know you need incontrovertible evidence and i hope today during our conversation i'll convince your friend and anyone else who's skeptical that you know we really um know quite well not just that they exist but also many of their peculiar properties we actually see evidence for their peculiar properties go ahead well i was going to say you raised two really interesting points there that i want to get into and one is how there are kind of different definitions of black holes what is a black hole we can answer those in different ways and depending on how you answer them maybe that that gives a kind of different window upon you know their behavior or understanding of them or how they manifest in the universe and similarly uh we've talked about um how we don't really see them directly and so there there are obviously ways that we can study them and we're gonna get into those in much more detail later uh but i wanted to kind of focus on on those things right now um about just kind of getting getting the fundamentals again and maybe we could maybe we could talk about that about about how there's different conceptions of what a black hole is um in the context of history right because people kind of we forget we forget that here we are in 2020 and of course everyone knows the black holes are real of course black holes are this thing but it's really i mean in the big scheme of human history it's a very new idea and it's so radical and you know and like all radical scientific ideas it you know it it was not easily accepted so one of the first people to really come up with the idea was chandra shikhar an indian astrophysicist who in 1935 actually had worked it out a little bit before um he was in cambridge england at trinity college and as he was coming from india to cambridge to study he had worked it out on the way on the boat well on the ship on his way he had worked it out that the end state of some stars would would be a very very compact dense objects and when he presented this is a famous controversy known very well in astrophysics where he made this presentation at the royal society and you know arthur eddington was one of the famous astrophysicists a senior astrophysicist of the day uh refuted it because once again he didn't like these peculiar properties of black holes nobody wanted to believe they existed so it took till about the 1960s when we sort of had the first evidence of the end states of stars so stellar corpses have you know there are different kinds of courses depending on the mass of the births birth mass of the star and so when they discovered one of the possibilities they knew that aha so the other possibilities could exist and so that's how you they really became real as in observationally but you know and i think that part of the reluctance um is because of what peculiar things these objects are they're so enigmatic i mean this is what i find so seductive about them right that you kind of think you understand them there are a bunch of different ways to think about them and you kind of hit a wall every which way that you think you feel slightly illuminated but then you can't grasp it so could we have the first slide please so we need to think about it yeah yeah so it creates sort of different ways of thinking about it and the reason these three different ways allow you to make sense of their properties and of course black holes are simultaneously everything right all these three things so one way to think about it is the kind of strength of gravity that they exert so for example a black hole the gravity is so intense that not even light can escape which is why they're called black holes so um so the way to intuitively think about it is you know if we launch a satellite from the earth say cape canaveral or whatever right for the satellite for the satellite to escape the gravity of the earth we need a rocket we need um we need to blast out at a velocity that's about you know 11 kilometers per second yeah and so that's the kind that's why we need the boosters we need the rockets right to boost it out of earth's um gravitational field so if you can imagine that gives you a sense of sort of the strength of earth's field for a black hole that speed that you would need to launch anything with is the cosmic speed limit the speed of light and of course we can't speed make anything get close anything material get that close to the speed of light so that's one way to think about it now real quick before we go to the next slide i want to i just want to unpack a few things that i'm seeing here in this slide for some of our viewers i'm noticing at the bottom there's a there's a strange term here it says schwartz child radius now i'm assuming Schwarzschild must be a person uh but can you tell me what that is yeah sure the Schwarzschild radius washer is a person this was named after carl Schwarzschild he is the person who right after einstein announced his theory of general relativity he was uh fighting um uh is world war one in the trenches he heard about the lecture worked it out got the solution of the black hole which is the sort of the intense gravity he mapped out the shape of space around a black hole and this was radius is sort of the sort of an odd weird radius region around the black hole that is also called the event horizon this is the point of no escape okay so you have a black hole it has this boundary called the event horizon and anything that makes it in including light cannot make it back out so it's the point of no return if you will for black hole and to give a sense again of why is the gravity so intense and how could it be and what do i mean when i say it's really dense and compact so if the earth were to have the kind of gravity that a black hole does all of us everything on earth would have to be crunched to the size of a penny everything including all of us right now talking everything yeah that's frightening it's really fantastically dense incredibly dance so could we go to the next slide please so another way to think about black holes and i think this is what i was mentioning earlier this is what chandra shekhar came up with right thinking of them understanding that they are the end states of stars so if you have massive stars so if you have the birth mass of a star to be about eight times that of the sun or above then after finishing its life cycle exhausting all its fuel it will actually explode and end its life as a black hole okay okay and then the way that works uh so we we mentioned that there's another kind of stellar corpse earlier and i think they might be pictured here all of them we have white dwarfs right white dwarfs and then there's neutron stars and then black holes right that's right like black peculiar properties the most peculiar properties neutron stars are intriguing in their each one is intriguing in its own way but you know neutron stars are just packed with neutrons right and a black hole is just much more compact and so a neutron star is basically as you said it's like a big giant neutron essentially uh you know what it's like it's a star the size of a city or something like that you know a teaspoon weighs as much as i don't know and uh and then if you just throw a little bit more mass on there a little bit more of something i guess like i guess i could do a couple different things so we don't need to get too technical but if you threw enough on there all at once presumably it would just collapse straight away to become a black hole that's right if you throw enough mass you could um and uh and the black hole is much denser i mean i think relatively speaking a black hole is much denser than a neutron star and it has this peculiar property of having an event horizon right and speaking of which let's let's go to the next slide as well because i think that that this is a good segue here um what i want to notice here and and i want you to take a lead in a moment but um we've been talking about you mentioned singularities earlier about this place this place where everything kind of comes together in a very literal sense and all our theories break down all our understanding breaks down we can't predict what happens um but that's not the same thing as an event horizon so let's let's just just no no no no right yeah yeah so so one of the fundamental contributions that you know einstein made the reason we all think um you know hero worship him is this profound profound way in which he was able to link mass the shape of space and motion so he sort of showed that sort of the geometry or the shape of space is defined by the distribution of masses so you can think of you must have all heard this analogy of the entire universe as a sheet a four dimensional sheet or a tarpaulin or something you know and every piece of matter in the universe causes a little pothole is pock marking the universe this sheet and the more massive an object the deeper the pothole the deeper the dent in this sheet and remember there's nothing unlike this figure where this sort of a cartoon you know there's nothing above the entire universe is the sheet we are all living on the sheet so there's nothing above there's nothing below so we are all confined you know all celestial bodies are confined to move in this sheet and let me just point out also let me add the other wrinkle right which is remember the sheet is expanding all the time it's not a static so i mean it's it's a complex kind of you know interrelationship between the shape motions and matter so if you look at how not only does the mass of an object determine the shape the depth of the pothole that it creates but how mass is packed in it so the density matters so in this schematic you see like the sun would cause sort of a nice big pothole and then you have a neutron star yeah in the bottom panel and um and if you have a neutron star notice it's much it's it's denser than the sun so it's going to have a deeper pothole and a black hole is going to cause a puncture in space-time that's how dense it actually is okay so we're so we're seeing black holes as you know products of einstein's equations as almost like mathematical entities we're seeing them as the end states of massive stars we're seeing them as punctures in space-time maybe that's the same as number one um and i just find it so fascinating that that you know we're talking about if you compress the entire earth for instance into a black hole now that would be an awfully small black hole i don't know if black holes could be that small can they be that small per year they could in principle they could in principle but you you compress it all and you think about all the books all you know shakespeare history uh uh the continents uh my memories everything all of it all of the bi you know the biosphere dna and it all gets compressed down to a black hole this little tiny penny shaped thing and then i don't want to do that we don't want that but there's another reason there's another deep reason why we don't want that which is the loss of information so once you cross the event horizon right something bizarre happens you because no light nothing can escape you we don't actually know what happens to objects that actually cross the event horizon of a black hole uh but we have some ideas but what we don't know is what happens to the information what is their mass what is what was that object right if i fall into the black hole i mean you would never know did priya have blonde hair did she have dark hair was she wearing glass no you there would be nothing you would know nothing you wouldn't even know there was a priya right right and this is a big unsolved problem so that is the peculiar nature of the event horizon because you know light is our cosmic messenger all information in the universe is transmitted through light we obtain that through light or some other kinds of waves like gravitational waves which we will talk about later right and we're just about to talk about them but before before we get to that next section really quickly i actually want to have there's one follow-up follow-up question there which is so we compress all this stuff there's all this information that goes in but what are what what are the fundamental properties of a black hole you've mentioned a couple but i want to make sure we have them constrained because it's only like a handful right i mean i could write it on my hand yeah it's basically three properties are needed to fully define a black hole it's mass it's spin whether it's spinning or not and uh its charge for most astrophysical black holes charge is not really a relevant quantity but so it's mass and spin so that's what we're really after in astrophysics we're trying to measure masses and spins because the measurements of masses and spins then we can confront that with our theoretical understanding of how black holes grow and so on and test our models but you know i can see why that's kind of abhorrent to einstein the total loss of information the fact like you can reduce all this complexity to just this bulk thing that just sits right yeah so you know there's a beautiful analogy that um stephen once um used and explained to me and i love it and he's presented this in many talks uh this is hawking so he said that you know it's like having an encyclopedia britannica and looking up say you know you look up new haven connecticut and you see you know where it is on the map you see the population 100 000 whatever right and then you you actually put the encyclopedia britannica in a box in a really tight box from which nothing can escape and you burn it down completely burn it down but you've caught every particle of ash inside that box nothing's left that box right so the information that was in the encyclopedia britannic is still in there it's just no longer stored in the form of pages and printed ink and so on so forth and we no longer know the act of reading like of actually accessing the information we don't have that either so the information is clearly there but it is in some form perhaps that is um that we cannot recover and we don't even know how it's stored so i think this is the best that you know the best analogy that i've heard uh and um it's an unsolved problem by the way of what really happens to the it's controversial their ideas and so on but no real resolution quite yet but i mean the resolution that we are inching towards is exemplified in this analogy that the information is likely there we just don't know quite how to retrieve it so we're not completely losing it it's that's the direction in which the solution is going so hold on we'll have to wait and see there's always a chance you're telling me there's a chance okay good let's um let's advance to the next slide i think it's another poll actually because we've been talking about i think it's another poll yes how do astronomers observe black holes and i gotta tell you folks priya already gave you some big hints right so let's go ahead and kick it off let's see what we can do we got about 30 seconds which of the following is a typical way that astronomers observe black holes is it a x-ray emission b gravitational waves those ripples in space-time that love to make headlines c stellar motions or d all of the above let's think carefully about this remember black holes are black we can't really see them directly yeah i think i kind of let the cat out of the bag a few times didn't only only for people who are paying very close attention i know some of you are are stroking your cats right now on your laps i know some of you are scrolling your phones shame on you you should be paying attention to me and appreciate come on it's the joy of the zoom universe it's true it's true we can all be connected in this in this crazy time of cobit despite being isolated in our houses ah yeah i can't believe how many months it's been right since i sort of i finished teaching a couple of months ago and it was all shifted online in march but um but i think what is really fun is that we're not letting this little nanometer-sized virus get us down man we're still thinking about black holes the universe all kinds of things about nature and the wonderful things that nature offers yeah if you're going to be bummed people we were more boned about falling into a black hole and never no i never knowing you existed okay here we go poll results uh we have x-ray emission five percent gravitational waves eighteen percent c stellar motions ten percent and d all of the above 67 percent a whopping 67 percent the ds have it all and that is the right answer and now now priya just as a segue into the next uh section that we're going to talk about which is called the black hole bestiary we can go ahead and get that next slide up uh i think it would be useful to talk about how we have these different observables and maybe they give us uh different windows onto different sorts of black holes just some some sorts of black holes right now for us with our current capabilities um present themselves more in one way than another when we're thinking about these ways to look at them does that make sense yeah well i mean i think you know um black holes first of all right they come in a range of sizes yeah right and their sizes determine the gravitational influence that they exert as we saw and therefore the ways in which they will render themselves um render their presence is going to depend on the sizes of these black holes so typically we tend to see black holes especially the super massive black holes these are we'll talk about in just a minute uh these are some of the most massive black holes in the universe like the one in the center of our own galaxy and remember these gal these black holes that are sitting in the centers of galaxies can be either fasting or feasting like the one in the center of the milky way um the supermassive one four million times the mass of the sun is actually fasting there's not much gas so that is swirling in so the way we typically see black holes is when matter is swirling in and it's being pulled in by the gravity of black hole gas typically it gets heated and it gets it gets hotter and hotter as it's getting closer and closer to the event horizon starts to glow and it glows in the x-rays and that's how we see most commonly feasting supermassive black holes so stellar mass black holes on the other hand they are having little feeding episodes so if you have a stellar mass black hole that is next to a star that strays close or it's bound to another star then it could start feeding slowly ripping the star apart and start feeding so once again that gas as it falls in so you always see sort of these dying gasps of gas around black holes then for the black holes like the one in the milky way we actually see them in a completely different way they are not feasting so what they do is they control the motions of the stars that are right nearby so can we go to the next slide please so these are actually real data from the center of our galaxy two different groups one from reinhard genzel and the other from the ucla group led by andrea getz and these are the same stars whose motions are being followed and this is real data so you see the clock on the top right yeah and notice that these orbits are closing in so it's like the solar system right we see the planets on elliptical orbits and the sun is one of the foci and you know the most massive object in the solar system is the sun similarly the black hole is really sitting right there and so we are able to measure the mass of the black hole by looking at these orbits so in the right hand panel you saw something more exciting happen and that was there was a little gas blob that came close to um the black hole in the center of our milky way and we we thought and we were really hopeful that we might see like a feasting episode we actually didn't we saw a little bit a trickle in and then it just zoomed past but you know it can't go too far it's in the gravitational grip of the black hole it's going to come back around and what you see with the dates in the future is a prediction of when that gas blob is likely to come back around wow so this is the way in which we have detected pretty much and measured the masses of all nearby supermassive black holes it turns out that almost all the black holes supermassive ones nearby are fasting so this is the way to detect them but then this method doesn't work for black holes that are far away because remember you have to resolve all the stars you've got to like map motion of every star and that's incredibly hard because the centers of galaxies if you see them are incredibly bright they're chock-a-block filled with stars so you can't resolve them till you have huge telescopes so next generation telescopes will allow us to go even further out than we have uh to detect these fasting black holes but it's the feasting ones supermassive ones that we detect much more easily because you see x-ray emission and then of course the dramatic new way in which we started detecting black holes recently was when two black holes collide and we have detected the collision of two stellar mass black holes so black holes come basically we categorize them in mass as in slim small stellar mass black holes the end states of stars very elusive we'll talk about this more in a little bit intermediate mass black holes that are about a thousand to ten thousand you know forty fifty thousand times the mass of the sun and then super massive are black holes that are you know million to a billion solar masses then you have the obese ones the ultra massive black holes that are more massive than billions of solar masses and the reason we you might say well this looks kind of arbitrary actually it's not arbitrary the way we've classified them because um they have different ways of being born so stellar mass black holes we've nailed it they're born and states of stars and the question of course for people like me who've been working in the field for a long time is try to see can you start from these stellar mass black holes can we like over feed them and make them intermediate mass black holes and then supermassive black holes and ultra massive black holes yes that is one way to do that but it turns out that there are many ways to make the first sort of black hole so-called seed black holes you don't have to start with just the first stars could we have the next slide please now real quick just for re for our viewers so they understand when you're saying that that the c black holes didn't have to come from stars is that because we're talking about so early in the universe that stars did not exist is that what we're talking about no it was probably these these uh what are called direct collapse black holes so these are basically when you have a lot of gas in the early universe um and it settles down into kind of a disk in the center of a galaxy no stars have formed yet in this particular galaxy but you know the gas siphons in because of an instability it's like you know you're sitting in your bathtub and you pull the plug and you see that vortex of water going in really really fast that kind of instability the pulling the plug kind of instability equivalent of that loosely speaking happens in the very early universe can happen and you can siphon a lot of matter down very fast because that's what you need to make a black hole right you need to put a lot of pack a lot of matter down very very rapidly and this we believe can happen simultaneously when the first stars form in the early universe and we believe that this is one way to make intermediate mass black holes you know a thousand to ten to the five times the mass of the sun very early on in the universe and of course from those you can easily build up the supermassives from these direct collapse black holes that are intermediate mass black holes in the very early universe you can build them up very rapidly to actually make very supermassive black holes even early on in the universe the reason you want to make them early is because you're seeing these feasting black holes which are called quasars out to the largest distances at the earliest times in the universe so there's like a timing crunch you have to really kind of you know as i said if you start with a stellar mass seed you have to like overfeed it and that's kind of challenging so but if you start off with a seed that's already intermediate mass then it's very easy to account for the supermassive black holes so here i just want to plug some recent work a paper that i just wrote so we wrote a paper a set of papers showing how you could make these direct collapse black holes more than 10 years ago but we recently realized that there was another way to make an intermediate mass black hole so if you form a cluster of early stars you form one of the stars actually gives you a little stellar mass black hole this little black hole could be bouncing around and eating a lot of gas feasting and kind of you know be a complete glutton and it could become an intermediate mass black hole in the very early universe so that we worked out and i recently realized i just submitted a paper a little while ago where you know there's no reason that cannot happen later on in the universe so basically continually you could form these intermediate mass black holes so you might say oh this is all great we're making all these intermediate mass black holes the problem is we're not seeing them in that stage so it's almost like you know you have the photo album of black holes you're seeing pictures in infants say you're seeing nothing in teenage and early adult years and then you're seeing kind of the older like midlife and the geriatric black holes so there's kind of a gap and so you know that is one of the open kind of puzzles could we have the next slide please i mean to be fair i i tried to kind of mask my aqua adolescence too so you know no one can find those pictures of the internet i hope yeah like you thought maybe that we should yeah maybe that's not a bad idea right we should all hide our pictures but you know i don't know i think you know i was actually kind of that was the time that i was actually pretty so that's too bad i don't have many photos but um anyway so this you know this is i wanted to show this movie uh because it's such a beautiful visualization it's from one of my recent phd students angelo riccarde what it the these are this is how black holes grow so black holes grow by eating gas by feasting and they also by colliding with each other so what you see here is the life cycle of black holes you start out as a cluster and that's a cluster that you have to start out with you see them growing by eating gas and colliding with each other and then eventually what you see at the um when they reach the top that is the real data of nearby black holes like our milky way is a point on that graph in that black cluster on the top the milky way black hole is there and so this shows you the sort of dissects how black holes grow over cosmic time so this is a time lapse if you will of the assembly of a black hole so an individual black hole the supermassive one that we see today has had a very complex history by growing not just feasting but also merging with many many other black holes and the reason these kinds of you know so it's a story line right so this is we've built this of course it's based on science and physics but this is a model that tells you how you can end up to explain everything that we see now so one of the intriguing things that we see is that that's what is shown on the right panel the size of the black hole that you find in the center of a galaxy in the central galaxy is adjusted to the size of the galaxy somehow the galaxy and the black hole know about each other as it were and this is where we come back to the start to our first question they somehow know about each other so they regulate each other so in some sense the inner part of the galaxy kind of controls the feeding of the black hole and as i'll tell you in a minute black holes actually kind of burp and so they're they sort of burp and they emit and push stuff around in galaxies as well so there's a kind of intimate relationship between the um the inner part of a galaxy the star is in the inner part of a galaxy and the black hole and so we've been trying to work out you know as astrophysicism is this just a mere correlation or is this actually causation so that's the deep question we actually think it's causation and that's what these models show you yeah you know this is kind of you know i i'm kind of an exoplanets and astrobiology guy i mean i really love black holes and fundamental particles all that stuff too but you know my heart isn't big dumb objects like that you can live on right but i don't want to fall into it and just become a wisp of plasma i hopefully can i want to talk to aliens um and i was wondering the relation to that is with this is um you're talking about this correlation that might exist this causation that might exist um between the central black hole the central supermassive black hole and the the environs the outer parts of the galaxy the whole galaxy as a whole so i mean doesn't that kind of mean you're cause i think people would want to say a lot of times oh who cares who cares about black holes sure they're out there doing their thing they're feasting they're famine they're they're fasting they're they're burping but who cares they're so far away it doesn't affect your life here at all but i mean isn't there if if a central black hole in a galaxy controls the size of the galaxy and can burp out things and cause problems doesn't that kind of to some degree mean that i mean we might actually we might actually have the central supermassive black hole the milky way uh to thank for our being here to some degree or maybe or maybe maybe it's just that you know uh there is a relationship that's a great question because i mean i think okay first of all let me like we are very safe we in the solar system are very safe from the central black hole of the milky way so let's not worry about personal fate but absolutely i mean i think that in many ways um we thought that black holes because you know in the grand scheme of a galaxy right i told you they're massive and all of that or if you take the milky way the mass of the black hole is 4 million times the mass of the sun the mass of the galaxy is 10 to the 12 it's a million times more so the black hole is really tiny it's you know in the grand scheme of things however it punches more than its weight in terms of what it does to regulate the galaxy so we used to believe when we first measured these masses right of black holes from the motions of stars like we just saw people thought okay you know what they can't count for much they're the mass budget of a galaxy they're nothing it turns out and so they must play a very marginal role so it turns out that actually they punch much more than their way they play a central role in shaping galaxies so one could kind of poetically say that you know maybe we wouldn't even be here if black holes and galaxies the centers of galaxies were not so tightly locked in right that the galaxy and its ultimate shape and its fate and what it looks like is shaped by the central black hole wow and and just one more thing i know we're actually moving on to the next section soon but i i want to clarify for people very quickly in this animation on the bottom right uh these little these little red dots those are those all actual data points or those things from simulations these are black holes so this is the growth history of a black hole that will end up and what you really see there on top is the clock and when it says zero that actually corresponds to today so that's what you want to end up today so so this is explaining and you know and what you see these models are very very rich so we can take a slice in different moments of time and we can match it to what black the black holes that we detect in the universe at each of those epochs so the model that i'm showing you is one that is well calibrated that is the best to date that explains all the data that we see okay and so that's the black hole best area and some we have the stellar mass stellar corpses which can get a little bigger we have intermediate mass ones we're going to talk a little more about those i think they're kind of mysterious and strange the adolescent period the awkward adolescents and black holes of super massive black balls then the ultra massive black holes the really the really big boys that are that are the centers of galaxies and and is that is that the entire best area are there any other is there room in there anywhere there is room for another sort of speculative kind of black hole um and you know i kind of said uh you know could they be tiny when you ask me so there's speculation that in the primordial universe very very early universe prior to the universe becoming matter dominated where prior to even sort of the fireball stage very early sort of seconds of the universe's life you could have formed a population of primordial black holes right and they would be tiny tiny black holes they would form and so but you know we don't have i mean it's speculative we don't have evidence for them and you know we're constantly trying to figure out because you know these little black holes primordial black holes you know that formed if they were more than 10 to the 15 grams they could have survived anything that was less than 10 to the 15 grams if it formed with a birth mass of less than that early on it would have evaporated by now we'll come to that later uh but the other guys could have survived and maybe they could have grown maybe they could have formed they could even be the precursors of some of these supermassive black holes so but that that is still pretty speculative because you know from that epoch in the universe we don't actually get any direct or even indirect data at the moment okay so um that is speculative so before we uh before we move on to like you know one of the ways in which intermediate ma black holes were actually unmasked recently it's like totally exciting because i wanted to talk about a little bit of personal history and personal anecdote right um which is you know we always think about so this correlation that we just saw in the previous slide between the size of the black hole and the galaxy the stars in the galaxy the inner regions of the host galaxy i mean one of the things so that result was published in 1998 and i was a graduate student at cambridge cambridge england and i realized at that point that if this little black hole had to somehow impact this large galaxy because remember this washed shield radius is tiny tiny tiny around the black hole okay it is it is well well well inside when we saw the milky way the stars moving around remember those toys are well outside this watch child radius almost a million times outside so the swastika radius is like a tiny region so right so if the black hole that is you could think of the black hole as the event horizon how does it have a reach that far out into the galaxy right so the first speculation so you know i was young and bold and radical and i said okay you know what we should there is a way in which we've always been fixated thinking about black holes as things getting swallowed into black holes what if this energy that is being emitted as matter is falling into the black hole could be tapped somehow and be used to push gas out it behaves like a piston that energy could be you know put in and you know assembled into like a piston outside well outside the black hole then i realized there was enough energy to push gas out to very large distances in fact even outside the galaxy outside the stars for sure and so that was a revelation i thought oh that's really cool so that's a burp so black holes can actually burp so it's not like the matter that goes in gets filled out it's on the way the stuff that is getting heated and you get energy that energy can be tapped in mechanically if you will you can think of it like a piston and then there's a piston that pushes all the gas that's around and it turns out that those gas blobs i realized that those gas blobs would glow in a very special way there'd be large bobs of gas and they would actually glow in the x-ray because they would cast a shadow on the cosmic microwave background radiation which is sort of the relic radiation from the big bang you know that's like a thermal radiation that is all around us even now we are bathed in it and early on in the universe this is because the universe is expanding this radiation has been cooling and today it's at three degree kelvin it's very cool it's not that's why we don't even feel it we're bathed in it but we don't feel it right and um and it's measured extremely well very very accurately but earlier in the universe it was hotter and so this hot gas is actually hotter than that relic radiation and it will cast a shadow and that that shadow should be measurable but this i wrote this paper in 1998 right after because i was trying somehow to link the scales the small scale with the big scale but we didn't have an instrument we didn't have we needed the alma array the atacama alma array and chilly telescope yeah it's a very large radio telescope many many dishes many frequencies and you needed this real wide span in frequencies to actually make this measurement and i was super excited because like less than two years ago they actually detected one of these first gas blocks and what is exciting about it is this blob is almost eternal relatively speaking it lives on forever so your quasar might have feasted and then be in a fussing mode which means we wouldn't see it and if it's far away we wouldn't be able to see the motions of the stars like in our galaxy yeah but this glowing blobs of gas would hang around and linger and so you would detect the presence of a quasar that was actively feasting ten to the eight years ago if you see these blobs this kind of reminds me of like uh you know maybe i i ate mexican yesterday and then i just you know i we should released on okay okay but i mean the point though is is that you could actually you could track the the quasars activity the big black holes activity through time and kind of see almost excavate previous meals and things you see exactly wow so does that mean does that mean that you could in some way maybe constrain or figure out um how quasars uh affect some this part of evolution of galaxies because obviously you need that gas you need that gas to form stars right that's right or prevent it from forming if it's too too hot it'll prevent the formation of stars that's actually what we think happens and that's how black holes limit their own growth so you have this gas that is too hot so you prevent the formation of stars right and so you keep this hot halo of gas around and the gas is not going to get um um you know it the gas gets fed in and then there isn't enough time to replenish for gas to come in from the outside to repopulate the inner region and so that is how black holes could stunt their growth they could eat all the gas and then the um evacuate the central region basically and then it may take too long for the gas to fill in and the other way in which so you know you raised a really important point that's worthwhile mentioning that we believe that quasars turn on and off episodically so they feast and then they fast they feast and then they fast so once a black hole is exhausted all the gas right around it it can get rejuvenated because it takes gas for gas to trickle in it takes a very long time but there's another way in which you can get gas if it goes quack with another galaxy so we believe that galaxies are constantly colliding in the early universe and when they collide you know their stars collide their dark matter kind of goes past and the gas collides the black holes collide and the black holes could collide merge produce what we call the gravitational waves which basically shake up that fabric of space-time that sheet of space-time gets tremors when the two black holes merge they become one and then you could have the lot of the gas still there so it can start feeding again it can grow it can grow by merging and then also a big feeding episode because when these two galaxies merge there's a lot of gas that ends up right in the center wow will we go to the next slide please yeah i think the next slide might be another poll let's see what's poll number three folks if you're still listening i hope you're with us how does a black hole die let's let's do it let's get to it how does a black hole die let's choose one of the following uh choice a it vanishes suddenly due to quantum fluctuations b it tunnels into another dimension or universe c it evaporates over almost incalculable periods of time or d it doesn't black holes last forever which is it gonna be i'll give you a hint priya mentioned it earlier were you paying attention i hope so yeah i think this question is something that people love to speculate about because you know we are so um hardwired to think about life and death and that you know the sense of of our own experience of life on earth that you know the sort of the notion of eternity i mean i think in a way that's what is so incredible about the cosmos right the kinds of time scales that um where um astronomers are talking about um they feel like eternity compared to sort of our lifetimes right well you know they say they say eternity uh uh you know it lasts a really long time especially towards the end right that's right but yeah so it sounds like i've always had the impression that you know black holes seem like these we can probably go ahead and put up the results i think um and we'll keep talking as we as we look let's see so okay poll results a advantage is suddenly due to quantum fluctuations only six percent said that b it tunnels into another dimension or universe three percent said that c it evaporates over almost incalculable periods of time 69 said that nice d it doesn't black holes last forever 22 oh the 69ers have it that is great that is the right answer it evaporates over almost incalculable periods of time uh priya tell us more yes so for example that is the right answer and for example um a black hole that's the mass of our sun like 10 to the 30 uh 33 grams or so that will last it will evaporate over 10 to the 64 years that is like super eternity as far as we are concerned because even on even you know by cosmic scales right the age of the universe is 13.8 billion years that's 10 to the 10 years roughly speaking so and of course the more massive a black hole the longer it will take so the as i mentioned earlier the only black holes that could have evaporated formed and evaporated sort of without a trace already or ones that might have been born at the big bang with a mass that is less than 10 to the 15 grams okay remember the sun is 10 to the 33 grams to just give you a feel right so those tiny tiny black holes are the only ones that could have evaporated so essentially black holes are eternal they're going to be there it'd be here forever so so i just got i just got i got to wrap my head around this real quick bro go to the next section i know i know we're kind of running out of time almost but i think we can still pack a lot of this stuff in um so we're talking about these things evaporating and i understand you mentioned steven stephen hawking earlier and obviously this is due to a process called hawking radiation which we can get into a little bit if you want to but but i had a question so everyone always talks about this slow sedate evaporation and i guess maybe it speeds up and gets more intense the smaller the thing gets um but what happens at the end like does it just kind of fizzle out or does it just explode at the very end like what is it like do we know well we don't know we think it becomes a singularity we're back again to a singularity right okay okay the so-called naked singularity where maybe it's just it's my mind's being blown right now okay and the other thing is just these time scales again so so you mentioned that that that black holes are going to be around practically forever anything above stellar slow mass and size um but then the super massive ones i mean you you you quoted a huge number that made my brain hurt uh the 10 to the 64th yeah 10 to the 64th is a is a solar mass black hole right these chinese stellar mass black holes we're already talking about just you know those that are detected by the ligo collaboration they've crashed into each other gravitational waves these guys would live for more than 10 to the 65 years they would live forever so i mean not only are black holes littered of every size littered everywhere in the universe tiny to the ultra massives they're also gonna basically hang around and be there they're gonna witness everything i mean i've heard some people speculate that you know people think about like proton decay the idea that the protons that are inside your atoms um are act in the nucleus of your atoms are actually going to decay at some point because they're not stable and so no one has i think the time scale picks that exactly but i've heard that you know the notion is that eventually they're going to decay which is bad news because then that means you just crumble apart into nothingness um so i guess in some sense falling into a black hole a supermassive black hole would be really bad because you would you would die um but on the other hand you would kind of stick around maybe longer than anything else right sure i mean it depends on what you want to do with your life when you're sticking around right i mean right i if i can't have my favorite flavor of frozen yogurt i mean life is pretty pointless pardon a silver silver lining every cloud yeah that's right if you cannot if you cannot enjoy doing science listening to music um uh creating and uh enjoying art we can't do any of these things what's the point of living forever i mean really yeah it's true so we should probably move on right let's move on that's right we're gonna have to go to kind of hyper speed we're gonna have to go faster than the speed of light now guys it's part three what comes next uh and let's actually go ahead and go to the next slide from here um we need to talk about next generation facilities and observations that are gonna really tell us even more about black holes the real dark frontiers so let's look at this uh so uh coming back to this elusive stage of intermediate mass black holes um so it turns out right so you might think as i've gone on and told you you know super massive black holes in the centers of galaxies and so on it turns out that's where we were looking for intermediate mass black holes so we were looking at tinier galaxies we thought okay you know what we know that the scale of the black holes and that of the galaxies they kind of scale that correlation so to find an intermediate mass black hole all we have to do is to look at a you know fainter and fainter tinier and tinier galaxy like a dwarf galaxy you know wimpy galaxy right that that is hard we're starting to have hints but the thing that we have missed and this was the very exciting detection and measurement now of the mass notice that little circle on the left hand panel so that is an image of a taken from chandra space telescope and the hubble space telescope overlaid x-ray and or and optical image and notice the little circle that is off-center yeah that's the intermediate mass black hole so we've been looking in the wrong places they're not necessarily at the center they're kind of wandering around in the outskirts of other galaxies that actually host supermassive black holes these guys likely off off-center then you might say hey how are we seeing them we're seeing them because they're glowing in the x-rays they're still feeding so some of them are feasting so you spit them up second this one was actually detected because of something called a tidal disruption event a star sadly skirted close by and got completely ripped apart and so that flare was detected oh that's that's uh that's that's that's disturbance into the force right there i'm guessing the planets probably uh wouldn't have a good time if their star got totally disrupted right that would be bad yeah that would not be a fate that you know i would i would you know we're worried about the story itself let alone the hanging on planets right and else possibly on those planets yeah we should probably let's move on but yeah so so we've seen some intermediate mass black holes though it sounds like and now there's other ways to study them with some next-generation stuff right that's right so i i mentioned earlier right so one way to detect black holes and measure their masses and their spins right is to actually detect gravitational waves from their collisions so the ligo collaboration already detected the collisions of nearby stellar mass black holes little ones and the the collisions of these supermassive black holes which are going to be in the centers of galaxies when they collide we will see a tremor uh in space time similar tremor but it's at a lower frequency so we actually have to be above the earth's atmosphere in a satellite so could you start the animation on the bottom yeah and so this is what is planned the europeans and nasa esa and nasa are planning what's called a laser interferometer space antenna so a configuration of three satellites and they will actually measure the collisions of supermassive black holes distant ones and the collision of a supermassive and an intermediate mass black hole so that's another way in which the intermediates are going to come into view very i mean this is an experiment that we think will fly in the 2030s or so and actually i'm part of the nasa leasing science team you know trying to generate you know models and understanding of what all should be detectable one of the interesting things about supermassive black hole collisions is because these supermassive black holes tend to be in the centers of galaxies there's lots of gas and stars and so on when they collide we will actually see simultaneously signatures in other parts of the electromagnetic spectrum because these gravitational waves are not part of our usual electromagnetic spectrum they are waves that travel at the speed of light because remember they're almost like they're waves in space-time itself so they're different from light right but the nice thing about supermassive black holes and it turns out some stellar mass black holes as well might have these counterparts we might have telltale signatures that we can see in the x-ray and optical and infrared so we might be able to actually nail down where the collision is happening because we'll see and a siren go off before the actual collision happens so that's the goal and of course james webb space telescope is in there and i'm of course deeply invested in it because uh once the telescope launches hopefully on october 31st next year uh we should be able to it will bring into view the first black holes the very first black holes that likely formed in the universe so if this idea of direct collapse black holes are forming these intermediate-sized black holes from the get-go bypassing the formation of a star remember from the gas and the vortex analogy if those are really there we will see them so that's what i'm most excited about because that's a window that's going to open uh first wow that is so exciting and amazing i hope we managed to be around for to see these things launched hopefully you know james webb next year and i i hope lisa in the 2030s you know we'll see it's pretty advanced tech but uh i'm sure we can do it we put people on the moon right so why not i mean and you know that the tech for lisa is already there was a test um uh a prototype and the prototype performed better than expected than specifications so very optimistic it's only now just sort of money and time that we need to build everything and test everything um and launch i think that is that was our last slide wasn't it i think we have one more which is just want to know more i want to plug your amazing book mapping the heavens the radical scientific ideas that reveal the cosmos excellent and then of course anyone who's interested in black holes could also check out scientific american in our ongoing comprehensive coverage um so we're a little over time only by two minutes though we went hyperdrive we nailed it no no i um i i want to add that you know i was very very excited that um scientific american sort of asked me to write about these first black holes and um it was an article that came out in february 2018 but i think it was republished in this volume that you have exciting discoveries in black holes so that's an excellent volume to get a special issue that's an excellent one to get there are many uh interesting articles about the frontier what's happening uh for black holes of all sizes i think we're gonna have to have you back pretty soon to write an update because it sounds like we're gonna have to rewrite the textbooks at some point the next couple of years again if james webb goes up and because i think that's my excuse so i have this report physics reports is very prestigious um place where we'd write review articles and so you know i've been waiting they've been asking me they asked me invited me to write a review on black holes and i said oh just wait there's this one new discovery and you know i heard a hint about this you know i heard a rumor let me wait and i'll hand you that article once i put that in but it's been non-stop i mean we've had these wonderful discoveries like pretty much you know even the last few months like every few weeks there's something exciting right so yeah it's crazy so more things to come and now now the part that maybe some folks have been waiting for you get to ask for your questions not just me with my dumb questions you could ask questions i'm going to read them off we're going to handle as many as we can we have until um can you hear me but now i can hear you and i lost that question i don't know if that was the trick that you kind of stretched it out and i had to figure it out i think it fell into a blackberry that shifted the question could you um repeat the question sure it's from ariel bach it is what is your favorite theory about what happens beyond the event horizon um i think okay so look there's in in in science right i mean science is like a creative process so there's like the real and the imagine so we take little leaps of imagination and then we figure out and work out the physics right so let me just quite clarify now that when we talk about anything inside the horizon it is pure speculation pure imagination okay so this is not scientifically a realistic option or a solution the thing i find most fascinating is when you fall into a supermassive black hole the possibility that you know that singularity could take you places right that it could potentially tunnel you and take you into a brand new universe i think i saw matthew mcconaughey the most important i think i saw matthew mcconaughey do that one time yes that's right that's right in interstellar yes yeah uh but i have to say sometimes right this universe and this earth i get really depressed right when i see you know the the reluctance to accept climate change and all the anti-science stuff i was like you know what i feel like tunneling out into a different universe man there are times when you really want that portal as well well folks i want to see more questions from you only have one of them coming up which gives me a space to ask another question right now here it is uh if you fell into a black hole uh i've heard some people say that you'd be able to see something really strange uh on the on the sky as you were falling in is there do you know what i'm talking about right so first of all um when you fall into a black hole it kind of depends uh on your point of view so if you are looking at things as a distant observer whereas you are the sad person who is hurtling in right so you see different things but the intriguing thing is that if you are the person falling in so the person who is sitting outside will basically see you hurtle towards the uh event horizon and the light from you getting redder and redder and redder and then you will basically freeze for them they won't be able to see anything right the minute you cross because no light can escape so they cannot see you anymore so this is the distant observer whereas meanwhile you the sad person who's falling in unfortunate fate you will see weird things when you fall into the horizon you would see the light from behind you bent because light is bent in strong gravity this phenomenon is called gravitational lensing so you would see the weird effects of light bending you would see um you would see everything getting redder than getting white and then you would see the cosmic microwave background it will flash by so you'll see very bizarre optical um i wouldn't call them illusions but i guess yeah illusions is the right word yeah you would see all these weird optical effects what about time dilation anything weird there yes of course time i mean you know time and space switch in terms of their place in the mathematical equation once you cross even horizon so um basically it would take you once again it depends on the person was really far away it would it would take in from that person's point of view you're frozen it would take an infinite amount of time for you to actually fall into the singularity from their point of view right but their point of view doesn't count as much because you're the sorry person who's falling in right right so once again if you are falling in uh to a stellar mass black hole remember it is much more compact it's a schwarzschild radius or the event horizon is smaller the size of the event horizon is directly proportional to the mass of a black hole so if a black hole is small the event horizon is even tighter so then and and the force the forces are intense right so as for a stellar mass black hole when you're getting close aside from all the optical effects one thing that's going to happen is that the let's say you're falling in head down first the difference in gravity between your head and your toes is going to be so strong that you're going to get stretched out so you would be spaghettified it's a technical term spaghetti i mean i always want to be taller i mean so that doesn't sound like that's one way i think this is like super desperate right this is super desperate yeah but then if you are falling into a supermassive black hole it's not as dramatic but you know you will become you will eventually you will become ashes whatever that mean you will not exist basically let's not go there is like what's going to happen to every individual atom in your body it's a pretty sad and violent kind of uh death nasty stuff we got another one from shintanu harad what is the mass of the biggest black hole that we know oh the biggest black hole that we know is in a nearby what is called a brightest cluster galaxy it's a galaxy that's the center of a cluster of galaxies and a cluster of galaxies is about a thousand galaxies held together by the gravity of dark matter and i believe the latest number that is published that i know is a few times 10 to the 11. there's an uncertainty in that mass so i mean i would say that for sure there are black holes that are 10 times 10 to the solar masses that's is that is that like hundreds of billions 10 billion 10 billion for sure i mean there are uncertainties in masses there are some there is one that's claimed to be uh closer to 100 billion okay okay um here's another one from an unnamed an anonymous submitter are gravitational waves quantized like waves are they evidence of gravitons um they're not quite evidence for gravitons um gravitational waves um we believe propagate through gravitons um loosely so you know we think about uh you know we think about light as photons uh similarly we think that um gravitational waves have gravitons associated uh with them we do not yet have um you know from the measurements that we have currently made uh we can reconcile that picture it doesn't mean that we've tested that picture or that we've detected them okay so gravitons we think they're there but but but we haven't we haven't found them yet there's no detector that said ping ping ping graviton is detected for sure okay um okay wow we just got a bunch oh just a huge number came in let me sift through them very quickly um why are black holes in the center's galaxies i think we covered that a little bit um unless you have more to say there's many more um let's see what do they want to um that was it just why are black holes in the centers of galaxies i think but i think yeah i think we kind of covered that a little bit i mean they're quite massive they end up they either form there we know that many of them form there to start with because i told you that you know the formation of the black hole and the growth of the black hole is intimately tied to the assembly of stars in the center of a galaxy so some of them are born there some of them end up there because of mergers they get you know twice and sent to the center and then we also believe that if you had that you know that intermediate mass black hole that we saw that was wandering in the outskirts we think it will eventually wander in and get pulled into the centers it could take a long time um and then some black holes could be lingering around right but in general you either make your way in wandering or during a collision or you're born there okay okay very cool so we still it's there's there's a couple of different options uh here's a fascinating one from uh caleb eridani uh what do you think will be the next multi-messenger method that most greatly influences our knowledge lisa neutrinos radio waves gravitational wave decryption or something mathematical wow that is a there's a lot of options there that's a lot of options i'm just going to pick my favorite um i think my favorite so multi messenger uh is basically this idea that you would see a phenomenon in many many different wavelengths obviously with some time delays because of the processes that produce them so for example one my favorite is lisa and the fact that you would see merging black holes you would detect the gravitational waves from these merging supermassive black holes or a supermassive and an intermediate mass black hole um or a supermassive and a tiny stellar mass black hole so you could see all these combinations um with lisa um that that is my favorite um multi-messenger phenomenon because in this case we believe that one of the ways in which though when two galaxies merge their black holes are going to merge so every uh black hole in the center of a galaxy has a feeding disk of gas that is sitting around it and that's called the attrition disk and so when the second black hole during a merger is brought in and threatening to the center it will fall plop into the accretion disk so that is gas and this gas will torque and drive these two black holes together in the final final stages right so remember black holes are so tiny that when two galaxies merge they're gonna miss they're not gonna you know you're not gonna be able to hit them and make them stick as it were and collide right on right they're gonna kind of miss gonna get you know trapped around each other grinding closer and closer and then it's gonna plop into that feeding disc of the bigger one and so the secondary will slowly kind of spiral in in that disc and that entire process of spiraling in because it's gas it's going to be glowing we're going to be able to see it feeding it'll feast because it's going to be embedded in gas so we'll see a precursor to the actual collision in electromagnetic components we might see it in optical infrared radio and so on and then after the two black holes merge remember there's still a lot of gas around in galaxies so after that there could be a superfeast there could be a gluttonous feast where basically all the gas that's left over in the center is going to go slack into the very massive black hole so you could see various stages and that's why it's my favorite in the multi-messenger you could see precursors you would then see so you would see precursors that would alert you a week before a year before months before then you would see the actual gravitational waves and then after that you could see a post-cursor another feeding episode of the very massive merged black hole now feeding and evacuating all the gas that's right around it so it's you know you would get an observation that is spread out over a couple of years and we can pin down so many properties of the system so that's why that's what i find super fascinating that is super fascinating and also i just want to say i want to lobby for you making those technical formal terms both plop and thwack when we see this i want to i want to hear i want to see those in papers so okay we've got to i'm going to get a bit of a reputation right like burp with quack i mean i have to kind of improve my um lingo now this is a here's an interesting one um it's from lisa holt she asks how big a role does dark energy play in a black hole's feeding slash fasting process interesting question so it turns out that dark energy actually plays no role because at some level right dark energy if you will is this large-scale uh countervailing gravity kind of entity in the universe so once a galaxy forms right it's like a little closed box it's its own little universe remember the galaxy itself is not expanding right so remember dark energy is what we think is propelling the accelerating expansion of the universe so once you form a galaxy you have separated out from the expansion of the universe which is why you know our galaxy is intact right it's not being spread out and expanded out our galaxy is intact the milky way and and we know that right even nothing is expanding like the milky way is not expanding the solar system is not expanding because we have so this is what we mean when we say a galaxy has formed it has separated out it has decoupled from the largest sale cosmic expansion and it's the larger scale cosmic expansion where dark energy is relevant and that is what is driving it on very small scales inside these objects are called collapsed objects in the universe a galaxy is a collapsed region of the universe which means that basically it's an airtight region that is its own entity and so the and you know the black holes are sitting in the center of the galaxy so by and large they are really not affected by dark energy of course the early formation of structure etc happened in the backdrop of dark energy being around except that now we know from you know dark energy was discovered only in 1998 right the accelerating expansion of the universe but we also know that in terms of cosmic epoch right that dark energy most likely was always around as the what we call the cosmological constant it's one of the constituents of the universe it's like the baseline energy of the universe if you will but that it was constant over time and that the universe went through stages where the energy of the radiation dominated then matter dominated and then late in the universe several billion years ago like five billion years ago or so is when we believe our universe became dark energy dominated so dark energy did not play a starting role it was kind of wading in the wings and has only sort of taken off in terms of its effect in the universe of course it's deeply important for the future of the universe of course yeah and actually that's a follow-up question very quickly uh there's more here but one that's bringing to mind for me is you know we talk about the different scenarios that exist for the future of the universe long-term we talk about the so-called big rip the big crunch and i guess maybe the big chill the big grip being where dark energy somehow accelerates run away exponentially and then you know next thing you know your atoms are being pulled apart ah i'm dead and everything's terrible uh there's the big crunch where somehow it ends up reversing you know as if as if maybe there's enough matter in the universe to pull it all back together via gravity doesn't sound like that's gonna happen uh and then it goes back to the singularity almost uh and then you have the big chill which is you know where it's almost like a flat universe and everything just kind of severely spreads out you get the kelvin style heat depth however um if there was a big rip what would that do to black holes do we know well um well we we believe that you know one way the uh the the big rip uh could impact black holes i mean you know it it it depends it depends on the nature of dark energy in detail so um i think it would be um we would have to work with a particular model to sort of work out what the consequences would be but what is very clear i think is the one of these three possible deaths the one that is easiest to visualize for black holes and galaxies and so on is the big chill so that's the one in which basically the universe is going to expand dark energy is going to cause the expansion to speed up and so the distances between galaxies is going to grow very very dramatically it'll be a very lonely and isolated universe and so the black holes themselves will be intact in the centers of galaxies but nearby the distance between nearby galaxies is going to grow so dramatically large wow so folks we only have about 10 minutes left but i think that's time for enough questions i'm going to try to squeeze in some more pre are we good on time you've got some more time yeah well i have a few more minutes so actually here we go so uh here is one from juan pablo salazar it is is there any theoretical basis for wormholes and would they be in any way related to black holes well um no um i mean you know you can think of if i want to be generous i can say that you know um we can think about wormholes this sort of this possible this imaginative thing where i said that you know you could tunnel into possibly another universe so that would be the wormhole um and i mean that's what we saw in interstellar right which was i mean in every aspect i love interstellar except for this one thing where you know there's this little wormhole near saturn or whatever right that they go go through um but um yeah no i mean they're speculative i wouldn't um yeah they're speculation mathematical speculation where's kip thorne when you need him kip kip log into the chat let's talk uh okay i think kip kip would also agree that they are speculative he he i mean i think he would like them to exist i mean so would i as i said right portals i also want to be mathematically so i mean maybe in that universe somewhere out there that can happen um let's see uh now here's one from oh oh i don't even know how to read this one hold on i'm gonna do skip on that one uh here we go um from hamad yusuf will spooky action at a distance we're gonna have to define that um will spooky action at a distance uh hold true when an entangled particle goes inside the black hole this is a good one all right this is a good one so let's just define split the action at a distance so that's quantum mechanics i think that is um spooky action at a distance it refers to the very smallest scale phenomena in which we have fundamental uncertainties so facts things like the uncertainty principle heisenberg's uncertainty principle right so where you cannot simultaneously measure the position and the velocity of a particle and and the kind of domain in which this separation between the observer and the observed kind of neat separation breaks down so the very act of measurement influences what you the system that you are measuring it tweaks the system right so uh so you know i'm going to interpret this question as sort of a big picture question which is that you know um right now we have not yet we've unified all the forces in the universe right the four forces in the uh the four forces that we know exist in the universe electromagnetism the strong force the weak force and gravity right so the goal is to unify all the forces and to but so far um gravity which is the force that governs the larger scales and is relevant over the cosmos as we discussed today has not been integrated with quantum mechanics which is the physics of the small so we don't yet have a theory of quantum gravity a theory of quantum gravity which would integrate these microscopic whatever phenomena with cosmic level sort of phenomena so a force that acts on those ranges that is the kind of theory you would need to actually explain what would happen to have a good quantum description of what would happen if a particle follows and falls into a black hole so one you know so this hawking radiation that we talked about earlier right so one of the kind of it's still sort of classical thermodynamics but that is kind of gives you a hint of the kinds of things we're talking about so you know vacuum is not actually empty right so vacuum is basically particles and anti-particles whizzing and coming together destroying each other and then kind of you know so they're called there's a constant whirl of particle anti-particle pairs and um and the hawking radiation and this black hole evaporation all of that has to do with the fact that right around the horizon when you have these particle anti-particles pairs you could occasionally have one particle go in um into the horizon whereas the anti-particle comes out right so you're actually losing energy if you will so um i think all i can say is that you know we don't quite have a relativistic and a quantum level deep understanding yet to talk about the quantum mechanics of particles that fall into but you know there are people working on it and there has been quite a lot of progress made and in fact um you know hawking was working on it till his last few days you know i i think that's a beautiful answer because you you answered actually about four or five different other questions in the queue right there uh and unfortunately unfortunately everyone we are out of time at this point um i wanted to just tell everyone you know that i hope you had fun i had a lot of fun uh i hope you had some fun priya and thank you thank you it's fun right so so you've shared your outstanding knowledge with us today and uh and everyone out there watching it again thank you and i just i want to say i have to plug uh at scientific american we look forward to seeing you all future webinars uh and uh in the meantime i really hope that you can uh follow us on twitter instagram and facebook also priya has twitter and it's a hot place for astrophysics news let me tell you check it out yeah and also i um i have a webpage if you want to read more a little more technical stuff on the papers and the work and look i love black holes and so it was the sheer pleasure for me to talk about something that i know it's really strange to say this but i really care about black holes i think maybe maybe again why are we here we could just be the product of the burp of uh yes and looking forward to many new discoveries meanwhile uh stay safe everyone all right i think i'm breaking up i'll see you guys i'll see everyone have a good one bye
B1 中級 米 Geek Out Session: What do we really know about Black Holes? 7 1 joey joey に公開 2021 年 04 月 28 日 シェア シェア 保存 報告 動画の中の単語