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hang on new video well done so today I want to do two objects at the same time or rather two double objects at the same time in particular double quasars so I've got two images here they look superficially very similar two little blobs but they're actually really different but it takes some detective work to figure out how different they are what you're seeing is double quasars so a quasar is a quasi-stellar object so it's something that on a photograph looks like a star just a point source but they are actually really luminous objects in the very distant Universe we think they are creating supermassive buttholes so when you do a survey with an astronomical telescope and you take
pictures of the sky and you see two little Point sources next to each other there are multiple explanations first of all they could just be Stars okay stars in our own Galaxy sort of very nearby they could be a chance pairing of one star and one Quasar and that would be very different distances they could be two physical quasars that are actually a binary pair close to each other or they could be something which I'll talk about at the end let's look at the picture on the left here this is an image of two quasars located together very close on the sky they are only 0.46 Arc Seconds Apart it's difficult to put that into scale so let's try if you take your little finger and hold it at arm's length that will just block out
the size of the full moon that is half a degree by half a degree okay so to get down to Arc seconds you have to take your degree chop it into 60 arc minutes and chop each one of those into Arc seconds then you take about a half of an arc second and you get the separation between these two it is very close together we need the power of the Hubble Space Telescope to distinguish them now the way that this was found was quite interesting wasn't found by looking for two things close together it was actually using the Gaia satellite Gaia is a satellite that has been scanning the whole sky for multiple years mostly measuring the positions of stars within our own Galaxy to an incredibly High Precision this is called astrometry but
it can also be used to find other interesting objects the discoverers used Gaia to look for objects that weren't double because Gaia couldn't resolve them but had some sort of funny jiggle to their light and they liken this to signals at a railway Crossing we have two lights that are jiggling on and off and on and off and so guy wouldn't have been able to see that there were two objects there but there would have been enough error unexpressed unexplained error in the measurements to cause some sort of astrometric access and so in finding these candidate objects that look a bit funny in the guy observations they could go with the Hubble Space Telescope and in this case find that is
actually two separate objects so observations with many other telescopes show us that they have different properties in x-rays in radio and if you take a Spectra you find that they're almost the same but with a tiny little difference so this is all sort of compatible with the idea that they are two physical objects that are actually very physically close together and in fact if you dig a little deeper in the Hubble Space Telescope images you can actually see tidal Tales evidence that they're sitting inside two massive discount taxis that are colliding and their stars are being thrown about and stretched into these big elongated tails that tell us it's a merger so pretty clear that this pair is a physical
object and we're seeing two supermassive black holes in the distant Universe at the epoch of High Noon Cosmic High Noon where the there was lots of activity in terms of supermassive black hole accretion star formation we're seeing two supermassive black holes in orbit around each other only a few kiloparsecs apart so that's smaller than the distance from our solar system to the center of our galaxy this is probably a silly question but they're also embedded within two galaxies that's right you've got two galaxies colliding at the center of them you've got two supermassive black holes now all of this happened in the distant past this is all over and done with by now we're seeing this as it
was 10 billion years ago the likely out come if we were able to see them as they are now is that they've merged into one massive black hole and those two disc Galaxies have probably themselves formed a fairly round and boring Stellar collection known as an elliptical galaxy so now the object on the right it looks pretty similar doesn't it we've got two point sources two quasars but these were discovered in 1979. so here's an image from the original 1979 paper showing the pair it's not very spectacular but it makes you realize the sort of needle in the haystack search that was going on to identify that something a little unusual here was happening and then to go and follow it up what the original authors
found was that these are two objects that are close together on the sky not as close as our previous pair this is six Arc seconds apart but where our other pair had differences in their observed properties these ones were identical twins they were exactly the the same redshift and it looked like they had very similar properties our final hypothesis is that it's actually the same object but we're seeing two separate images of them through a phenomenon known as gravitational lensing here's in the abstract difficulties arrives in describing them as two distinct objects and the possibility that there are two images of the same object formed by a gravitational lens is discussed they cracked it they knew it so a follow-up
paper by many of the same authors showed a more detailed Spectrum this is object a object B we're seeing the fingerprint of the elements in this object as a function of wavelength and they are absolutely identical and if we go back to our original image you can actually see on the right hand side here a little fuzzy red thing and that's actually an intervening Galaxy and that's what's doing the lensing this galaxy is part of a galaxy cluster the light from one distant Quasar has come through this galaxy cluster thanks to general relativity it's been split along two separate paths when we get it when it gets to us we see them as two distinct objects it's just an optical illusion
and in fact there's a time delay as well because the light is taking two different paths to get to us it's actually passing through slightly different areas of space and it's taking different amounts of time and so should something like a flash go off in one it'll take 14 months before we see it in the other and one will have traveled 1.1 light years longer than the other one that's cool foreign
