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GMT20210426 180133 Recording 1920x1080

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00:08
hello everyone hi welcome my name is fiona welcome to our astronomy talk for this evening or it might not be evening when you're watching this uh this meeting is uh being recorded this webinar so you can you might be watching this later or it might be a different time where you're watching us in the world because looking at the chat and we've been asking you to let us know where you're watching from i'm in edinburgh so i normally work at the royal observatory in edinburgh i should say my name is fiona if you haven't met me before
00:39
and i've noticed that we have people from all over the world watching so i think we have america uh venezuela i saw romania india ireland all over the uk um where else oh canada brussels every single country you can think of so welcome everyone thank you so much for joining us it's brilliant that you can all join us uh here for our talk this evening uh hello from blackpool as well hi not far away so um i'll just go through a couple of
01:10
things before we start you may know these things already if you've used zoomed a lot before so it won't take me long so you've already noticed that there is a chat function as we said you can use that to say hello to the panelists to me to matt who is in the chat and he will be there if you've got any technical problems as well so if you can't see or hear something if you ask matt in the chat then he can try and help you out also on your toolbar as well as the chat button you should notice
01:41
that there is a q a button so you can submit questions for our speaker which we'll get to at the end of the event you can do this at any time and we will be asking questions at the end as i've said so uh one final thing as well so we've got the chat we've got the q a and the last thing you might notice is that we have auto transcription for this event so it's not perfect as you might have seen if you've got it on you can hide the subtitles if you want to you can also change the size of them
02:13
if they're getting in the way of other things on the screen or you can hide them completely if you don't want to use them okay so that's everything i think i need to say other than introducing our speaker for this evening his name is phil short and he's an astronomer at the royal observatory in edinburgh so i think he's lurking in the background somewhere so phil hopefully you can hear me hello hello i can hear you but i can't see you i really am my video's going oh there we go there we go there you are fantastic hello how are you doing
02:44
not too bad thanks yourself good yeah i'm really good we've got a bit of sunshine in between the rain at the moment in edinburgh so yeah too bad not too bad so can i um hand over to you to start your talk you're all ready yeah absolutely let me just show you scratch brilliant and there we go uh can you just uh can you see the slides okay yeah that looks perfect thank you so much phil fantastic okay uh yeah so thanks um thanks everyone for coming today that's
03:15
a fantastic attendance from all over the world i'm phil i am a phd student in edinburgh and my area of research is in active galactic nuclei and tidal disruption events so uh don't worry if those that particular secret words doesn't mean anything to you right now uh if i do my job okay then hopefully by the end you shall understand everything um so um before we go into these astrophysical phenomena um i first want to discuss the thing
03:45
that links to two things which is uh black holes uh so what is a black hole exactly uh there's a few different ways you can define a black hole uh but i think the simplest way to do it is that it's a region of space from which nothing not even light itself can escape and um the reason for this is that you have a huge amount of mass a lot of matter in inside a tiny little space and uh yes so this uh exerts an incredibly strong gravitational pull
04:17
um and not light not even like an escape um and we define the the region around the black hole um from which there is no return it's called the event horizon so this is the point in space from which you will have to be traveling at the speed of light to be able to escape um so this is the escape velocity um you may have heard this term before so um on earth the escape velocity is about 11 kilometers per second so that's pretty rapid um if you were to throw a ball from the ground upwards
04:48
at this at this speed it'll be able to make it into space um we can't but you know we can launch rockets up at that speed um but the speed of light is a uh a speed barrier that nothing can cross um and that's that's how we define the black hole uh so there are two sort of flavors of black hole that we we usually usually look at in uh astronomy these are uh the stellar mass black hole and the supermassive black hole so as you might expect the stellar mass
05:19
black hole is about the size of the mass of a uh of a star so these are typically a few solar masses and what i mean by solar mass is um well a solar mass is the mass of the sun so the sun weighs 2 times 10 to the 30 kilograms that's a 2 followed by 30 zeros which is a really big number and not one that we want to deal with on a regular basis so instead we say the sun is one solar mass and base everything relative to that um so yes a cell mass black hole is
05:50
typically a few solar masses in size and typically around tens of kilometers in diameter and this diameter i'm referring to is the the size of the event horizon essentially the radius of the event horizon and these types of black holes are formed uh from dying massive stars so when a star um that's massive enough uh runs out of fuel in its core so it stops fusing um hydrogen and all the other elements uh there's nothing to support it anymore so it starts to collapse
06:21
and if it's massive enough then the gravity will be able to overcome any pressure going on in the inside and it'll just collapse all the way into a black hole there's many of these in our galaxy probably millions of billions just floating around not really doing much this one we see in the picture here on the left is a it's a black hole in a binary system so lots of stars form in binary systems where it's two stars orbiting each other and then if one dies before the other one then you get a black hole and a star and the black hole tends to accrete material so it sucks material
06:52
from star onto the black hole but the type of black hole we're interested in today is the supermassive black hole so these things are huge right they are they can be anything from hundreds of thousands of solar masses to uh tens of billions or so that's it's absolutely enormous um and they're typically sort of roughly solar system size so they're kind of um the distance from sun to pluto so uh usually a little bit smaller actually um so you've got um tens of billions of
07:23
solar masses potentially um in a region the size of the solar system which you know our solar system has star a few planets and a bunch of rocks so it's a little bit denser than that um and we think well we're pretty sure at this point that these types of black holes uh reside in the centers of all galaxies including our own milky way but we don't actually know exactly where they come from uh so there's kind of a few possible methods that we've come up with one being that um back in the early universe there are
07:54
these huge uh clouds of gas that sort of condense down under gravity and eventually form these black holes and the other potential um formation mechanism is that they came from the first start of the universe so uh they they died and became sort of stellar mass buckles and sort of gradually built up as the universe went on um but i said we usually see these well we think that these supermassive black holes uh like the centers of galaxies um but how do we know this uh i just defined a black hole as being a region from a region um
08:26
from which not even light can escape so how do we see these kind of things uh and the trick is to look at not the black holes themselves but the effects they have on the stars and gas around them um so what i'm going to play for you here which hopefully you will be able to see clearly is a video um zooming into the center of our own galaxy the milky way and seeing what the stars do when we get right into the center um so i apologize if you can't see this clearly but what you should be seeing here is uh we start off with a nice video
08:58
a nice picture of the milky way as you might see it from earth if you have really good vision and um a very powerful telescope like we do here and we just zoom in um these images are uh sort of a collage of images from the vlt the very large telescope in chile which is one of the most powerful telescopes that we have at the moment um there's some more powerful ones on the way but this is this is still pretty good um so you can still see we're still zooming in here uh maybe don't get too close to the screen because uh it can be a little bit
09:28
dizzy in this video um okay so we're now getting to the point where the stars are starting to look a little bit blurry now hopefully it was it was nice and that crisp before that um and now we get into this point here where we're right into the central region so if i'm pausing the video now um because what we're going to see here is basically a stop-motion film of about 20 years worth of images taken um by eso so this is the observatory in chile which has the vlt
09:59
um and what i've done is record the motions of stars in the middle of the galaxy over a period of 20 years and sort of condense it down into a few seconds so what i want you to do if you can is observe this star in the middle uh i think you can't see my cursor but there's a bright star in the middle and just just watch how that star moves oh no we started again hold on [Music] okay here we go so hopefully you can see how that star just zips around the middle there
10:32
so um what astronomers actually did um was measure the speed that the star gets up to and actually reaches three percent the speed of light which is an incredible speed for a star to get up to um and what that means is that it's got to be um orbiting something that's very massive and in fact when they when they go for the mass they figure out that the the mass of the object that they start to be orbiting is 4 million so masses so it's a lot of mass and it's in a tiny little area so how do we get a lot of mass into a
11:03
tiny area it's a black hole um so that's yeah that's how we measure basically the the mass of black hole in our own galaxy the supermassive black hole that is um but this is easy right this is um this is only um eight kiloplus x's away which is what uh uh 24 like 24 000 light years away uh it's nothing um so how do we observe that supermassive black holes in galaxies that are further away um well the way we do that is is this
11:34
okay um is by looking at active galactic nuclei so the supermassive black hole in our own galaxy and in many other galaxies is that dormant what we call quiescent which means it's just sitting there just happily chilling doing black hole things uh not really doing a lot um but in some galaxies these black holes are in an active state so this is what we call an active galactic nucleus and what that means is that there's um a whole bunch of gas and dust around the
12:06
black hole that's falling onto it and this produces loads of light um a tremendous amount of light but how is that possible a black hole doesn't let light go um that's because it's not the black hole itself that's emitting the light but the the matter that's falling onto it and actually um these things can get so bright that just that central region of the galaxy can outshine the entire rest of the galaxy so all the billions of stars that make up that galaxy can be outshone by this tiny little
12:35
central region excuse me um so it'd be criminal of me not to mention at this point uh the recent result which is the uh event horizon telescope which uh it was 2019 now the eht so what they did here was they combined and a whole bunch of radio telescopes from around the world and using this method what we which we call interferometry so this essentially allows us to combine a whole bunch of telescopes from around
13:08
the world into one giant super telescope and that's what the eht was and they pointed it at one of the nearest aegean on the brightest again as well in our vicinity which is m87 agn by the way active galactic nucleus just makes it easy to say um so yeah what that allowed them to do was um really zoom in on the central region so this picture on the left is from the hubble space telescope and you can see basically the galaxy is a hole and it's very bright central
13:40
point in the middle hopefully i've kind of blocked it out with the arrows but okay and what they did is zoom right in on that and actually what we're seeing in this sort of orange image on the right is a disc of material around the black hole that's uh being accreted onto it and this black sort of shadow in the middle is the black hole itself or at least a shadow as casting this is an incredible result and i know it doesn't look like much from here but believe me it's uh it's very impressive and um it's not
14:10
something we've been able to achieve of anything else the problem is that most agn are a lot further away than this um so how are we supposed to figure out what's going on here i told you there's a black hole in there but you know and the lights being produced by mata falling onto it but how do we know that how can we see that if we can't actually resolve it with our own telescopes so for that we're going to look at the electromagnetic if i can say it properly the electromagnetic spectrum
14:40
um so um agn very conveniently uh emit light all across the en spectrum um at all wavelengths and we can look at these different wave bands to figure out uh what's going on different structures at play so hopefully you're familiar with the the em spectrum to some extent uh so at the short wavelength side on the left um we have x-rays uh so short wavelengths mean higher energy and when it's higher energy we usually think higher temperature and then we move along to
15:12
the ultraviolet um then visible which is obviously the the region of light that we can see with our own eyes and then it comes to longer wavelengths with the infrared and the radio and what you see is that agn actually emits in all of these wavelengths so first we're going to look at um the ultraviolet so uh ultraviolet light is emitted by this disc around the agn so this disc um where it comes from is essentially as matter falls onto the black hole or
15:44
towards the black hole it tends to interact with itself and circularize is what we call it and it forms this disc of matter around the black hole and we call this the accretion disk this matter is being accreted onto the black hole and as the material spins around the black hole um it's releasing energy it gets incredibly hot and um like you may think of you know like if something if a piece of metal gets hot it emits light uh same thing happens here so the gas gets really hot and emits
16:14
a lot of light um and as you get to the center so closer to the center of the black hole the disc is hotter so it's emitting at higher energy and it's around here that we see the uv wavelengths being emitted but as you actually get further away from the center and out towards the edges of the accretion disk the temperature goes down slightly i mean it's still hot but it goes down and actually extends down into optical wavelengths of visible band but the brightest um the the wavelength
16:46
range that the accretion disk is brightest in is ultraviolet the uv wavelengths um so we're going to pop that onto our little em spectrum here and that's this is a key part of the accretion disk uh that's sorry a key part of the agm the accretion disc because this is what's producing most of the light you see or at least what it's going to see and so then we're just going to pop back to the x-rays quickly um so x-rays are produced um not in the accretion disc itself but in this sort of region of charged
17:16
particles that lies above and below we don't know exactly how this works to be honest so i'm not going to go into the complexities but it's somewhat similar to the corona that we have um at the edge of our sun i know corona but yeah so what happens is these charged particles get um they interact with these really strong magnetic fields and um basically get super heated and admit in x-rays and this is really handy actually for finding uh agn at long distances you know what's a long
17:46
distance in space but the real really long distances um we can spot x-ray but we can spot agn by looking for the x-rays um so that's where the x-rays come from and um yeah so we've covered x-rays and ultraviolet so we're where we've been looking at the accretion disk and the corona and now we're going to move on to the visible part of the spectrum the optical light so this is a graph um it might look hideous to some of you at the moment um but i assure you this is really
18:17
interesting and it tells us a lot of information so um just a quick recap of what a spectrum is so you take an image of say a galaxy a star whatever you want to take a picture of but instead of producing you know your regular image that you're used to seeing we split the lights up into its conceptual wavelengths and make a plot like this so um along the x-axis we have the wavelength so on the left side we have the shorter wavelengths so higher energy and we call this the we tend to call this
18:48
the blue end of the spectrum so it's a shorter wavelength region so we call it the blue end and then that extends all along to the right where we have the red end of the spectrum so this is longer wavelength and lower energy region and then on the y-axis is just this um what we call flux uh that's just a fancy word for brightness essentially um brightness per unit area if you want to know but essentially what you need to know is wavelength along the bottom brightness along the y axis now so what are we looking at here we've got a series of squiggles what do they mean why do we care
19:20
um well so let's ignore these spikes that we see for now and just look on the sort of overall shape of what we're seeing so if we start at the on the right at the red end of the spectrum and work our way inwards to left we see that it starts to slope upwards uh it's brighter at shorter wavelengths than it is at longer wavelengths and what we're seeing here is actually the sort of tail end of the accruing disc emission so i said before that the accretion just peaks at the ultraviolet wavelengths
19:51
well if we carried on this slope that's leading up to the left if we carried that onto shorter wavelengths beyond the range of this particular instrument we'd see that peak in the ultraviolet so that's what the kind of overall shape is from it's from the accrual disc itself um but what's uh perhaps a little bit more interesting here are the spikes so these spikes are what we call emission lines and i'm just going to quickly take you for a little bit of science to explain what they are and why they look like what they do
20:22
i assure you it's hopefully nothing too complicated so hopefully you've uh you recognize this little diagram here that i've created as the hydrogen atom um and not the scale um what we have is uh in the nucleus there's a proton that's bothered to be charged and the orbiting around it is a negatively charged electron currently in the ground state so that's the lowest energy that the electron can have in its orbit now what happens if we move this uh atom
20:52
close to an accretion disk excuse me um well what might happen is that a photon of light so this is just light from the accretion disk um might hit the atom and what happens here is that the the electron absorbs the energy and jumps up uh an energy state so they can jump up one it can jump up to it depends on the energy of the photon that comes in but the electron doesn't really like sitting up here it's unstable it wants to jump back down to the ground state so after some time it does that again
21:28
it can either jump all the way down or it can jump along at different energy levels along the way um but in order to do this it has to release energy so uh what it does is it emits light instead of so it initially um it absorbed light from the approaching disk and now to get that down again it's a little light and this um this light that emits is what produces a mission line and um we can we know exactly which um [Music] emission lines different elements could
21:59
have met because we can we can do this in the lab it's the same stuff hydrogen in the lab is the same as hydrogen space um not entirely true but sure enough so we know we can tell from uh which emission lines you see what which elements were present um but you might be thinking um well hang on a second if this if this um electron is emitting light at a specific wavelength then why is the emission line um not just a straight line why is it got a width to it um because if it was just emitting at one wavelength then we just see a
22:30
straight line going upwards well in order to explain this we have to look at another physical concept so this is the doppler effect now um this is probably uh something you might be most familiar with uh when it comes to traffic so um most of us would have heard the sound when a car comes towards us and goes further away we get this right um we've all heard that um so what this is is when the car comes towards you uh obviously submitting a sound and um
23:02
the sound wave gets compressed as the car comes towards you and it gets compressed it goes to a shorter wavelength and emits a higher frequency um then as the car goes past it drives away the sound wave starts to get stretched um so it gets stretched to a longer wavelength therefore it's emitting at a lower frequency and that's where the sound comes from well it turns out that the same thing happens to light so um let's say that someone's running towards you really fast with a torch what happened is that the wavelength of
23:32
the light coming from the torch will get squished it will become a shorter wavelength and so it will appear bluer what we call blue shifted and again if that same person is running away with the torch then the light will become redshifted it will become a longer wavelength um and we can this is what's producing our broader measurements so if we just take a look back at our line um so on this graph here it's the same thing as before uh wavelength on the bottom and brightness along the the y-axis on
24:05
the vertical axis and what we can see is that dash line in the middle is the true wavelength of our admission line um so if everything was stationary this is this is the wavelength that the line would be admitted to that now um you can imagine that if we have some gas um a gas cloud a cloud of hydrogen that's emitting uh this emission line if it's moving along and sort of perpendicular to our line of sight so it's not getting further away from us it's not um getting close to us then it's then
24:36
that's going to be admitting um at the central wavelength the wavelength we'd expect that's what i've highlighted in green here um but if there's a cloud of gas moving towards us then it would appear blue shifted so appear at a shorter wavelength because that wave um the wave is being compressed as it comes towards us excuse me um and the same thing um if there's a cloud of gas moving away from us it gets red shifted uh so it goes to longer wavelengths um as the wavelength is stretched and what you might kind of see here is
25:06
that this is actually um rotation so when we see a an emission like like this uh it's actually a cloud or several clouds of hydrogen um orbiting around the central black hole it's rotating so some of it's moving towards us producing blue shifted light some of it's moving just you know perpendicular to our line of sight producing the the true wavelength of the emission line and some of it's moving further away uh producing the redshifted line um and this is a really useful thing um not
25:37
just in agm but in astronomy in general so if we go back to our spectrum here um you can see that um some of these lines are quite broad so this one sort of between 600 and 700 nanometers it's quite a sort of broad line it's also quite strong but then if you look at around 500 we've got these very narrow lines um and basically what that tells us is the speed of the gas so you can imagine that the the broader lines um represent more redshift and more blue ships and
26:09
therefore the gas is moving faster so it's moving towards you faster it's moving further away from you faster and that makes the line very broad whereas these narrow lines um the the rotation is less uh the sorry the velocity of the gas is less uh it's not being blue shifted the rate of this much and we can use this velocity um the velocity of the gas supposed to tell us um sort of the distance from the gas to the hole so the broader the lines the faster it's moving the closer it will be to the black hole and we can also use this um to help
26:41
us figure out the mass of the black hole which is incredibly useful um so the visible part of the spectrum is not only interesting for us because we can see it but also they can use it to determine some really interesting things about the gas and the black hole itself and hopefully that all makes sense to you um so uh we have a creation dysporina in the x-ray the acreage itself in the ultraviolet and then the visible the main thing is these broad and narrow emission lights which tell us about the gas
27:10
um then as we move into longer wavelengths we get to the infrared so infrared emission we tend to think is um basically reprocessed emission in space uh so what we think is happening here is that the light from the center of the um the agn so the the light from the accretion disk is actually um impacting on some dust that's surrounding the uh the central agent um the central engine we call it the central black hole so lights hitting this this uh cloud of dust
27:42
um and uh the dust absorbs the light it gets it heats up and then it sort of radiates uh this energy away in the infrared we call this uh the dusty taurus the sort of ring of dust around the black hole uh but i prefer to call it a dusty donut because it's just uh it's a big dusty donut that surrounds the black hole and emits in the infrared um so that's the infrared for us and then uh last but not least we move on to radio so when we observe
28:14
agm radio wavelengths we see these huge plumes of uh gas essentially being fired out of the galaxy on massive scales we're talking sort of mega particles here so millions of light years um massive scales um and um yeah so what this is is um obviously it's extremely high energy um [Music] a gas being flied out of the galaxy and this is basically originates from magnetic fields right in the disk
28:46
itself so right in the center um these charge particles basically are being fired out of both vents and as they kind of zip around as these parts will zip around the magnetic field lines um they emit in the radio wavelengths and they don't just submit in the radio they emit well basically all across the spectrum but um the other key region is that they also emit x-rays which we can detect as well but it's very very impressive jets and like there's a huge amount of energy involved
29:16
so that brings us to the end of our tour of the uh of agn in the electromagnetic spectrum uh so we can start to piece this all together and build up an overview of what's going on in these objects uh so this is um a schematic picture of an agn so anyone that's ever been to a talk about agm will have seen this it's definitely overused but it describes the situation very well so what do we see here we have obviously the black hole in the center so this is the the engine that's producing all this um
29:48
high energy emission and around that we have our accretion disk um and then in the the region sort of above this and also below it we have a broad line region so this is uh clouds of gas that are quite close to the black hole and moving very fast and that's where we get our heavily blue and red shifted lines the broad lines and then above this we have a narrow line region so similar thing but it's further out and therefore the the lines appear narrower because the gas isn't moving as fast and we also have our jet being fired out
30:20
of both ends and we have of course dusty donuts surrounding the whole thing um so um you might imagine that if we if we completed the donut and sort of blocked off our line of sight to the middle that's something we can't see the increasing disc in the middle we can't see the borderline region and uh we actually see this um so some agn um we can see everything in this diagram so the uh the emission from the disk the emission from the broad lines
30:49
and the narrow lines um but in some agm we don't see the um the broad lines or the emission from the disk itself and that's because the um the dusty donut is obscuring our line of sight basically um and so it turns out that this picture actually works pretty well um this uh grand unified theory we call it uh that links all agn together um and so yeah so this is a basically a picture of what an agn looks like and what's going on inside it um and they're particularly interesting just because the sheer amount of energy they produce
31:21
has a drastic effect on the galaxy that they um they occur in so we actually think that uh every supermassive black hole in every galaxy goes through its phase so we in the milky way our own black hole went through this and every other galaxy um basically goes through this particular face um so this is probably a key moment in the in the evolution of the galaxy um because as it's driving out all this energy you can imagine it's also driving out huge amounts of gas and dust that would otherwise go on to form stars
31:52
um so these agn actually shape entire galaxies it's very useful and well very important thing to understand and while we have a good understanding of them it's not perfect and there's particular things that we don't really understand too well what some of these things are exactly how the accretion disk and the jet form exactly how they how they operate um and one tool that's sort of starting to be used to understand these more is a tidal destruction event so this is
32:23
my particular area of research at the moment so what is a tidal disruption event well essentially it's when a star that's orbiting around the center of a galaxy um gets a little bit too close to the black hole in the middle and gets ripped apart by the immense gravitational forces so this is very nicely summed up in a video which i'm about to play so apologies if this doesn't work very well to everyone i recommend going and finding these on youtube um you can just search tidal disruption event or tde as we like to call them [Music]
32:54
so hopefully you can all see this um so at the moment uh the camera is there was sitting in an accruing disc around the black hole um you can see this ring around the black hole that's actually just the light from the accruation disk on the other side being bent around uh gravity's so strong can bend the light which is crazy and there we can see a star is approaching um and as it gets closer uh we start to see it get stretched out comes a sort of rug musical shape until eventually
33:25
rather emphatically it gets absolutely destroyed um so about half the material gets flung out and an unbanned orbit never to be seen again well the rest forms this really nice accretion disk similar to how it is in an agn and also these jets shooting out on either side um so yeah and this is just again switching back to the accruation just view you can see things are starting to get a little bit more hectic um and yeah so this is our picture of a tidal disruption
33:55
tde um and what's uh particularly exciting about these things is that um well first of all um they allow us to find and measure supermassive black holes in quiescent galaxies so galaxies where the black hole is not doing anything right so i said before that in distant galaxies in order to be able to find a supermassive black hole we need an agm because that's what produces the light um but these tdes can happen around any supermassive black hole so uh like one in our own galaxy for instance it can happen or
34:27
uh yeah and any question um any dormant black hole and it can allow us to just to see the effect of black hole to measure it um and even more importantly we can see how things like the accretion disk in the jet form and really understand their origin so they're proving to be it's a fairly new field in astronomy and they're proving to be very useful tools um so now i just specifically don't need to play that again yeah so you're moving specifically onto my work here self plug so
34:59
we observe this object el diablo the reasons for that will hopefully become clear soon enough um so what we're seeing here is an image on the right of the galaxy it looks pretty you know not particularly interesting it's a fuzzy blob with another fuzzy blob next to it the orange blob uh is just a foreground star so that's good in the way of the shot rather annoyingly um but the sort of the greeny white blob in the background is in the galaxy and then in our spectrum so again sorry as before we have wave length
35:32
along the bottom brightness uh up the vertical axis um it's a pretty it's a pretty boring spectrum to be honest um it's pretty standard this is basically just what happens when you have lots of stars in the same place and split up their light so it's a sort of um yeah a messy line essentially we've got absorption lines here rather than emission lines which is when photons get absorbed self-explanatory really um but yeah it's pretty boring there's nothing going on but um in november 2018 a sky survey
36:04
so sky surveys are proving to be really useful tools in astronomy this is essentially where well a telescope surveys the sky funnily enough um but no the the these telescopes to take images of the whole sky every night and basically monitor the changes um so um it might take a picture of a region which contains a particular galaxy one night and take the same take a picture of the same region the following night and see that suddenly there's a bright light in this galaxy and this is either going to be a supernova
36:36
or a tidal disruption event or something interesting and that allows people like me and the collaboration i work with to jump on these objects and take spectrum so in yeah november 2018 last year a sky survey spotted this galaxy going bang a bright light appeared in the center uh not quite like that um but that's my impression um so we took a spectrum to see what's going on and as you can see that was a drastic change so we had this this white spectrum before which is just
37:06
a standard spectrum of galaxy sum of all stars um and then um yeah a couple of years ago we took another spectrum and suddenly it looked like this was a huge difference um so the key things to point out here are first of all that in general this new spectrum is a lot brighter it's higher up in the graph so it's brighter and also it looks bluer so this is what i was saying before when we were looking at our agn spectrum our active galactic nuclear spectrum whereas you go from
37:36
right to left so from the redder wavelengths to the blue wavelength it gets brighter um so this means that it's got a lot hotter and we can see again that it's sloping upwards to the left out of the out of the graph out of the range of our instrument which means it probably peaks somewhere in the ultraviolet gap like our agm and what we've also seen appear are these sort of weird very broad but quite weak emission lines so whereas before in our agn spectrum they were very sort of um
38:07
pointy and well defined now they just sort of weird blocks um which is interesting in itself so what we did over the period of the sort of next year and a half or so as we carried on taking spectra of this object um sorry if you can't see this part too well by the way um not too important basically we have our initial spectrum is the red one on top um and then sort of more recent one is down at the bottom and it sort of descends downwards and the key thing to point out here is that um as time goes on uh the spectra gets
38:39
fainter so the object is getting fainter and um yeah it's sort of starting to revert back to the original spectrum um what was particularly interesting about this object was the shape of the emission lines so on the right is the emission line that we were looking at earlier from our agn our active galactic nucleus and on the left is a zoom in on one of the emission lines from our tidal destruction event and you can see that they look completely different and they're the same wavelength region it's the same emission line so this is a
39:11
hydrogen atom uh with the electron going from the third to the second level if you're interested and what we have on the left is this sort of weird um if you ignore the weird sort of lump to the left which actually we weren't too sure what that was um then we see we kind of have this double peaked shape so it goes sort of vertically upwards steps back down again and then comes back up on the right and then sort of drops vertically and and this is where we we got the name el diablo so we double peaked uh also it could be say double horned
39:42
like a devil that's the name um and what this means is where is the um or what we think it means anyway is that where the agn emission line is from a cloud of gas orbiting the uh the black hole we think this double peak dimension is from the accretion disc itself i won't go into the glory details but essentially if you model what an emission line looks like from an accretion disk so if you use a computer code to figure out what's going on it looks something like this and this is really exciting at the time because we haven't seen this in a tde before at least not so clearly
40:15
it's clear evidence of an accretion that's forming um and it really kind of promises to reveal a lot about the creationist themselves and um yeah so that was that was my work i submitted this paper last year um and yeah i think that's pretty much everything i've got about uh that particular thing um so i won't bombard you with any more information so i'm worried there's been a little bit too much uh so we're just gonna have a quick summary so key points to take away if nothing else
40:45
uh supermassive black holes are these giant black holes of the centers of galaxies so these can be billions of times the masters are absolutely huge some of them are dormant so they're not doing anything like the one in our own galaxy whereas others are active these active galactic nuclear and these are consuming clouds of gas and dust in the vicinity and emitting tremendous amounts of light out outshining the entire galaxy potentially um and then third thing i wanted to talk
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about was tidal destruction events which these are the stars that are being torn about torn apart by these black holes so these can allow us to find um black holes that are otherwise dormant and therefore not observable and also allow us to kind of try and understand what's going on with an of galactic nuclear themselves and hopefully um that's all made sense to you uh so thank you all for watching here's a picture of me in front of some telescopes to kind of show my credentials and astronomers
41:45
and uh ready to take any questions hi thanks so much phil sorry um you can stop sh oh well i'll let you leave that up for a second actually just in case anyone's uh noting down there i just wanted to say that if um so there's not time for some questions uh people can feel free to email me oh we've got plenty of time yeah we do have quite a lot of questions but we'll see how many we can get through but yeah um as phil said if you do have any other ones you can email you will fill directly which is very kind of you um or also i'll put up some
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information about the vista center email address as well so you can always contact us there or on twitter as well where is that picture phil that looks like um is it the top of um one of the mountain top observatories yeah so this is in chile um la silla uh where i was lucky enough to go in 2019 while i still could yeah when we could travel those are the days but we'll get back to it soon very soon very soon okay and could you stop sharing your screen just so i can see you a little bit bigger because you're very small at the moment there
42:50
you go that's the hat oh the chat's been going off yeah so we've had a few people in the chat we've got loads of questions so um let's have a little look so some of these it might help actually to go back to some of your slides if you want to so the first one is somebody's asking about gamma from agn so gamma radiation is that a thing at all i know you mentioned all the different parts of the electromagnetic spectrum
43:21
yeah so um gamma radiation is gamma rays even are those most energetic part of the spectrum sort of beyond x-rays and it's not something we really observe in agn um maybe slightly but it's not sort of a key a key area that we look at that's okay um oh gosh it's so hard to choose this is the problem there's so many good questions okay so another one about aegns what role can adms play in star formation are they purely destructive creatures i like
43:53
the way you describe them as that right so um yeah so obviously yeah they can be destructive creatures so this is what i was saying about how as the uh the adm produce a lot of light a lot of energy they can push gas outside well out of the galaxy and therefore stop star information from happening but um and maybe this is what the question is alluding to they could potentially also increase the rate of star formation so by disturbing the gas that's going that's in the galaxy it can cause um an increase in pressure and
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basically kick off star formation rather than stop it so yeah there's a bit of a balance going on now bit of both fantastic we've got lots of questions about black holes it's always a fantastic topic something that always sparks the imagination we do have other talks more specifically about black holes and dark matter and dark energy all these kind of mysterious things um let's see we've got quite a few what can you please explain what it makes what makes a black hole active and what makes it dormant could
44:56
you just explain that again yeah sure so dormant black hole like the one in our own galaxy is it's just sitting there it's not really doing anything um absolutely you've got stars orbiting around it but nothing's falling in it's just sitting there um where an active black hole or this active galactic nucleus is just where it's it's constantly got the stream of material that's falling onto it and that's what's um yeah producing all this energy that's what makes it active sorry i'm off because these questions are so imaginative
45:26
okay um if nothing escapes a black hole is the escape velocity faster than light speed and what about time um what about time indeed um so we define the event horizon which is the sort of the boundary maybe can think of it as a surface of the black hole but it's not really um but this is the point at which you'd need to be traveling at the speed of light to escape the black hole um obviously you can't travel to speed of light unless you're light um so at this point
45:57
you would just fall down you carry on falling down and at that point yes you need to travel faster than this we look like um as for time um i might not be the right person to ask about this um you don't have to pretend you know the answers to it i don't know the answer but i think this is the name of something that no one really knows the answer properly um basically space and time are linked um black holes are places where space gets a little bit funky and therefore people theorize that time to get a bit funky as well
46:28
we'll go with that as far as i can yeah as phil says there's um lots of different topics and areas of research at the observatory and there are other talks as well that you can watch on our website which cover things like as i said black holes and also and things that was recently one about gravitational waves there's a couple of questions about gravitational waves so there's a whole talk about the the history of the discovery of those if you're interested in watching that um let's have a look okay this is an interesting one why is the
47:00
emission line symmetric if on average the universe is expanding shouldn't there be a slight asymmetry to the red end of the spectrum this is a very good question um so um the expansion of the universe uh what this does is it causes a red shift right so everything is shifted into a longer um wavelength um if it's moving away from us um and so um it's probably maybe slightly too subtle for you for you to be able to see
47:31
in the graph but um while the line itself is symmetric the the position that it is on the spectrum is redshifted so the shape of the line is due to the disc um but its position is due to the expansion of the universe that makes sense i think so yeah okay let's see this one's a good one do the forces inside a black hole tear apart atoms leaving a soup of quarks and other subatomic particles i
48:01
don't know if this is more a kind of um we need a fit of more of a physic physicist a theoretical physicist or i'm not sure do you want to have a go at that one or uh probably um so i guess it's sort of relating that maybe the conditions inside the black hole are maybe similar to what they were like at the beginning of the universe where everything was just this soup of particles uh we don't know what it's like inside the black hole to be honest not very pleasant yeah i can imagine okay and let's have a look
48:33
so someone asking specifically about the accretion disk of m87 okay someone's asking how are we able to see the accretion disk of m87 if it was shrouded by an agn ah so this is a yeah this is a good question so this is um the accretion is part of the agn first of all uh the agreement is what is emitting most of the light that we can see um and what i was saying about this sort of dusty donut that surrounds it um whether or not we can actually see
49:04
the disc depends on the orientation of the of the agn to us so if it's side on then the dusty donut will be blocking our line of sight to the disc but if it's face on like his decatur with m87 we can see the disc i like the donut analogy okay i'm getting loads of adverts from google about donuts now it's just making me hungry really i just wanna okay um oh this is a nice one someone's asking
49:34
what drew you to the study of tde so that's from rosie in glasgow what drew me to the study of tds um that's a good question um something obviously i don't know yeah so i mean actually when i was when i was looking for when i was applying for phds i didn't really know exactly what i wanted to study um i like all aspects of space um but uh yeah i came to edinburgh and my supervisor basically really sold tyler the shop's events to me i mean it's a star being ripped apart by a
50:06
giant black hole what's not to love to be honest yeah if i can argue that it's useful for science and great okay so this question is um yeah more of a specific one i guess more more about you by your career and where you've come so how long does a tidal disruption event last ah okay um so typically sort of around the year roughly they they do vary um so the one that i was studying that's el diablo i think it was about a year and a half
50:38
on we got a spectrum and it seemed to overall faded down um some are quicker some last longer some seem to reignite so that it starts emitting light again which is really interesting we're not entirely sure what's going on uh but yeah so around a year roughly okay all right i think we'll do a couple more i'm just saying i'm scrolling down and questions are appearing as i'm yeah this is the problem with zoom there's not an easy way to organize things um but you're also curious i love it okay let's see um
51:11
okay someone's asking how often tidal disruption events happen uh yeah that's another really good question um the short answer is it's um once every 10 000 years per galaxy so this is something that we've sort of worked out statistically but it also depends on the type of galaxy um so they seem to prefer to go off in galaxies which have recently had um sort of a merger event so two galaxies have combined together to form one and that kind of makes sense we think that stars are being thrown around like
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crazy um but yeah so not very often um but there's enough galaxies out there that we can observe them relatively often that makes sense i think so i think we'll have to stop that so if any of you there's quite a few of the questions still open sorry we haven't got to all of them it's a really interesting topic and so i'm not surprised but if we haven't answered your question and you do want to get in touch with phil and you just saw his contact details or what i'll do now and before we finish and just say thank you again to phil for
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a really great talk um by yourself yeah good it's good um so hopefully you can see can you see a slide just now with some information yeah yeah um so as i said if you want to watch this recording or any other recordings of our previous talks they're all on our website so if you just go to www.roe dot ac dot uk forward slash vc which is for visitor center and if you go on the section public events and you can find all the upcoming talks and previous talks
52:47
and you can also watch this one again because phil said there was quite a lot in this talk quite a lot of information graphs if you want to rewind and pause and take down notes of anything that you missed then you can do that uh matt i think in the chat let you know about our next event coming up which is on the 10th of may and that is another talk um all about some more cosmology and some interesting things which is very exciting so please do join us for that
53:17
and um also as well as i said if you've got any questions if you want to follow us on twitter we're at royal ops and also if you want to join our mailing list you can join it from the website there's a little um box you can enter in your details in or you can use that link as well i think that matt's put in the chat or maybe take a photograph i know you can't you can't click on the link unfortunately but we do send out information every now and again about the new series of talks and events that we're doing still online so thank you again to phil thanks so much for speaking to us all this this evening
53:49
and thank you to you all watching all over the world i hope you've enjoyed hearing all about i can't say them now these long active galactic active galactic nuclei and tidal disruption events there you go you can understand why we have so many acronyms yeah i can understand why that was a bit of a challenge so thank you very much and we'll see you all again very soon hopefully bye
54:57
you

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