Wandering Supermassive Black Holes and Where to Find Them – Dr. Michael Tremmel

is it is a former University of Washington graduate student Meetup got his PhD no I have to call the doctor Michael travel from the earth thanks for having me so today I'm gonna talk about some simulations that we have Ronnie that predicts that galaxies like our Milky Way actually have several gigantic supermassive black holes wandering about that we don't see and maybe we'll never see but they exist out in the galaxy floating around and so that's what I hope they convince you of in this talk but first I'm going to start from the beginning so when I talk about black holes there's sort of two two types of black holes that now we think about the first one are stellar-mass black holes and these are I find them to be a bit pedestrian if I'm honest so I know hello miss Lu style mass black holes but there's there's many of them in every galaxy mean we know about them for a long time every vein acid star which there's lots of them in the galaxy ends up exploding as a supernova but the the only part that explodes is actually the outside of the star but the inside the core of the star collapses and forms a black hole which you can't see because you can't see a black hole but this black hole is about the mass of our Sun so you think about it incidences these black holes are like if you take all the mass that our son has and cram it into an infinitely small point in a black hole and they're very cool you know if you're into that what I like to think about are a bit more exotic than that supermassive black holes these black holes are millions or even billions of times the mass of our Sun so millions of billions of times more massive than those stellar-mass black holes and one of these we know exists in the center of our galaxy and we know that because some very smart people looked at some stars moving around the center of the Milky Way and they can track the orbits of these stars over many about 10 years or more and they found okay these stars are moving about an object that we can't see and so you can do Kepler's laws very easy math and you can see oh there must be something very massive and also very very small at that point in the middle there ends up the only answer that makes and since is a black hole that's about a few million times the mass of our site that exists in the center of our own galaxy this is this is pretty crazy to think about the two behemoths black hole that's pretty close to us actually I mean relative extinct but actually all galaxies are most galaxies have one of these supermassive black holes at their Center in fact these black holes can do a lot of damage to their galaxies so these black holes whoa they can actually fling off a lot of mass into the galaxy so these are images of two two particularly cool galaxies that have a black hole at their center and that little black hole which is big but is actually the size of our solar system so compared to a galaxy is pretty small but it's causing gigantic outflows of gas that even sometimes dwarfed the Galaxy itself you can see in this picture here this guy innopolis the galaxy is this small thing in the center so this black hole is disrupting entire galaxies all on its own which is really interesting so there's a lot we want to know about these black holes how do they affect their galaxies as one but also where do they come from and how did they get so big these are clearly not from stars exploding so where'd these black holes come from well as with anything in astronomy to learn about it we have to look at it but as I said black holes are invisible so it's hard to see them but luckily for us lots of these supermassive black holes because they exist in the center of the galaxy have a lot of guests around them and because they're so massive they can match yes gravitationally and I eat it more or less that gas falls into the black hole and as that gas falls into the black hole it actually gets very hot and very bright and so even though we can't see the black hole we can see this guess that's moving around it and being eaten by the wrong cold and oftentimes these black holes I get right there's a computer-generated one from the movie time we can talk anyway so these he's my cold actually can not only today do they fling out all this gas but they can get so price well the gas around them gets so bright I think outshine their entire galaxy so we can actually see these black holes very far away from us and then towards the very beginnings of the universe itself and we use this using all these telescopes mostly space-based like Hubble Chandra and well sometime soon Jaime we have steam but the problem is is that when we look at what goes in this way we're limited because in order to see the ones that are far away we can only see the ones that are extremely bright and often the ones that are extremely massive but to understand where they come from and how they got to be so big we really want to see them at the very earliest times in the universe that's really hard because you're only you're only able to see the some very rare bright ones and even that there's lots of stuff in the way so if you fill all those billions of years back and try it between you and the black so you're seeing lots of stuff and getting away and make it hard to see okay so recently you might have heard a gravitation of waste in the news and so far using Lego which actually exists in watching one of the like of detectives is in Washington State they observe the merger of two stellar-mass black holes so loneliness what's interesting is if news today okay a lot of galaxies and have supermassive black holes in their centers we also know that galaxies merged sometimes and this here is showing a simulation of two galaxies that you know with the simulators base of English they made their galaxies from scratch on the computer and they flung them together and then saw what happened and what they saw is that the central black holes in these galaxies also end up coming together and forming a binary black hole and eventually merging together and with two supermassive black holes merge just like stellar-mass black holes they invent gravitational waves they orbit around each other and create ripples in space-time that you can detect with detectors here on earth now LIGO won't be able to see these black holes do you think of gravitational waves like sound why go sensitive to a certain frequency of sound in space-time but these black holes are urban higher pitch frequencies and so you need something well a bit a bit bigger actually to detect it so what we planning I'm doing is watching something called Lisa the laser interferometer space antenna and this will be three satellites orbiting the Sun orbiting Earth and orbiting the Sun connected by lasers but event measuring how space-time is wiggling how these ripples are passing through these lasers and it'll be able to detect mergers of supermassive black holes all the way back to the very very earliest stages of the universe when the universe was only a few million years old a hundred million what that's really interesting because this is a whole new picture that will have a new window into the supermassive black hole that we have never seen before which is really exciting so Lisa is gonna fly it roughly fifteen years or so so we got some time but people like need theorists are going to kind of predict what what sort of things will Lisa actually be able to see how often and where will these black bolt mergers take place and in reality these the simulation I'm showing here is kind of a live galaxies yeah this happens sometimes it's a very idealized case but in real life in the real universe this is how galaxies form small little galaxies form at early times this is showing gas in a region of the universe small galaxies form in early times and those small galaxies merge together to form bigger galaxies and those bigger galaxies merge together to form using bigger galaxies etc there's a lot more message there's a lot more mergers taking place one right after each other the galaxies are changing with time the properties are changing over time the black holes and those galaxies are changing over time and so the question is how many of these mergers of galaxies will result in a black hole merger to all and what happens to the black golden those ones that don't urge so that's what we set out to ask do this during my PhD I'm here at here in Seattle I developed a simulation that I call Romulus uh what what what the simulation is it's a big volume of the universe a big chunk of the universe that we put it dark matter and gas and all the physics that we want we're running on a gigantic supercomputer it took something like I think 75 million CPU hours to run the simulation so it ran for several months on hundreds of thousands of computers and in the simulation we the simulation naturally predicts like you saw in that video all this structure is filaments of gas and dark matter in the form and the galaxies is that form of these no points here so this image here is showing us gas temperature so these hot regions here are actually dense galaxies forming some of the big some of them small here I'm looking at the Stars and showing you what the stars those galaxies in play we have a variety of colors and shapes some of them are all alone some of them are in big groups and what we could do in this simulation is we can watch the simulation go through time and we can pick out events like this we can pick out where two galaxies are merging together and we can look at what the black holes are doing during that merger how are they moving around relative to one another and how long does it take them to actually merge together an event that would create gravitational waves or maybe they've never merged together into actually relatively brittle this is all purely a prediction of our simulation which is nice because we're not putting anything too much and then we can make a prediction for observations from Lisa and what we find just like those simulations I showed you before the idealized simulations of individual galaxies we find that that also happens in our simulations we have a galaxy merchant the points here the dots members of the black holes and see it is possible to have a merger of galaxies that bring together those black holes relatively quickly those two black holes merge together to become one as those galaxies merge and bring them close together but this actually doesn't happen all the time we also have cases like this so in this case we also have emergent 2pcs but the black hole ends up taking billions of years to merge so this final picture here the black hole's look kind of close but they're actually going to take another billion years moving around the galaxy before they merge together and so what's the difference between these two cases is that in this top case here hopefully I guess those the back right now so let's see again this both of the black holes have a galaxy around that this spot this this secondary Michael here you can always see a galaxy around there the galaxies existence is dense clump of stars and those two galaxies interact with each other and bring the black holes together but on the bottom this what this black hole here is all lovely there's no galaxies around them anymore it's just by itself wandering around the galaxy and it takes up a long time for that black hole to find its companions and murders so we can understand this a little bit better with the movie so what's happening here is that that small galaxy that brings that other black hole in ends up being destroyed by the bigger galaxy that small galaxy gets ripped apart by the gravitational force of the bigger galaxy as it interacts leaving the black hole all on its own and so this is a more extreme example here so inside the people in the back also might have a hard time seeing this there's a smaller galaxy down here with the white point of the black hole and small and red and it's gonna fall into this bigger galaxy this is right from the simulation and if you watch this black hole it's galaxies right around here is being torn apart this galaxy that used to be this little puffy bucket around the black hole is being torn apart by the bigger galaxies and destroyed and it's not to leave this black hole all on its own so have we seen the black hole up here and the black hole is gonna lose its galaxies and all by itself this black hole the supermassive by foolish about a million times the mass of our Sun is left way outside the galaxy the places where it will remain for billions of years and even trillions of years before ever the cost of these maintenance of the center and find its companion and so this actually happens quite often because merger like this are very common in the universe mergers between big massive galaxies like the magnet life simulations those are actually relatively rare and so the result of this is that big galaxies massive galaxies like ours that have gone through a lot of these versions remember to grow as big as they are actually we predict have many of these supermassive black holes so we already understood that there's a central black hole supermassive black hole in both galaxies like our own but we were predicting here is that there's actually several other ones though you can't see we've never seen them before because they're they exist so far away from the center of the galaxy so here's a couple images from the simulation of two Milky Way light galaxies and the white points and the arrows show the black holes at when their velocities are and so these black holes are on a very wide orbits randomly strewn about the galaxy although actually not quite random because it may notice where these black holes are they tend to if you look at these sidon images of the galaxies they don't actually exist in the disk so galaxies like ours have a disk of gas and stars and these wandering black holes tend to preferentially exist outside of that disk and that's because the black holes that would exist at the disk have had shorter time scales to fall tennis engine so the ones that stay behind the ones that have a very long time to reach the center are the ones that buy based purely on luck from the galaxy mergers exist outside of this galactic plant so that's the negative thing but it means it's a problem to see them because the disk of the galaxy is what all the gases that's the stuff that the black hole can eat to become bright but these wandering black holes is million solar mass black holes wandering around that halo in the Milky Way don't have any gaps around them to eat so they remain invisible to us and so this is now the next step and the research is trying to figure out how might we actually be able to get observational proof that these black holes exist and it's hard and I don't know the answer right now but that's that's where we're at so the simulations they have to predict that these massive galaxies in a series of these destructive mergers end up having several behemoths black holes wandering about very wide orbits that still at least for right now aren't visible to us even invisible to gravitational wave Observatory is like what you like Lisa so not even gravitational Williams can help us see these guys for like now yeah so that's that's the conclusion thanks for listening and I'll take your question [Applause]