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Current time:0:00Total duration:9:15

Video transcript

what I want to do in this video is talk a little bit about quasars quasars and that it's a short form for quasi-stellar quasi-stellar radio sources radio sources and this name is just a byproduct of the first observations of quasars because all they look like were these kind of point-like sources of electromagnetic radiation mainly in the radio part of the spectrum so that's what we call them quasi-stellar radio sources now it turns out that they are neither stars or even quasi stellar and they're actually not even that their main energy isn't even being released in the radio frequency in the radio band of the electromagnetic spectrum they're far more energetic than that what they really are what they really are the active nucleuses of galaxies so let's think about that a little bit so if we have a supermassive black hole at the center of a galaxy so let me draw that right over here so that's our supermassive black hole maybe that's the surface of the event horizon of the supermassive black hole the actual mass of the black hole is in the center of that event horizon if there's material that's falling that's passing by this black hole it's going to get attracted to it and it's going to form an accretion disk around it this material is going to start rotating around this black hole and some of it if it doesn't have enough of velocity is going to actually fall into the black hole so you have all of this material all of this material going around the black hole and some of it if it doesn't have enough angular velocity not enough not enough to orbit around the black hole it's actually going to fall in now while things let me label this this is the accretion disk accretion accretion disk so as things are getting are getting faster and faster as they fall closer and closer this black hole and bumping into each other more and more that gravitational potential energy from things falling into it is to being turned into actual energy actual temperature and so you what you have is things start to get really unbelievably unbelievably hot near the surface near the surface they get hotter and hotter as they closer and closer to that event horizon and so near the event horizon itself things are so intense that they're actually releasing electromagnetic they're actually releasing high frequency electromagnetic radiation mainly in the X in the x-ray part of the spectrum now I want to be very clear so there's two things here one is when you watch when you learn about quasars or you when I first was exposed to quasars in like a nova special you you they make you think that the quasar that the radiation is somehow being released by the black hole itself and I want to be and I would scratch my head because I was just told that nothing can escape the event horizon of a black hole including electromagnetic radiation so how could that be being emitted by the black hole and the answer is it's not being emitted by the black hole it's being emitted by the matter in the accretion disk that hasn't quite gotten to the event horizon yet once it's inside of the event horizon it can no longer any electromagnetic radiation that it might emit will not be able to escape the black hole anymore will not be able to escape the actual event horizon so all of this is from the accretion disk around around the super around the supermassive black hole and the other question that used to pop in my mind is why is it kind of come out at these why does it come out at these kind of perpendicular orthogonal to the plane the plane of the actual accretion disk and they're just you know at least my logic tells me well things aren't going to pop out and they're not going to pop out along the direction of the accretion disk because then they're going to be absorbed by other things in fact that's what's going to cause other things to get heated up closer to closer to the actual event horizon so any energy that's going out in that direction is just going to be absorbed and make other things hotter and only when you go roughly perpendicular to the plane of the accretion disk is that energy allowed to kind of go and transmit freely into space now I want to be very clear quasars are the most that these these are the most luminous things that we know of in the in the universe so most most most luminous things that we know of in the universe the the brightest or many quasars are on the order of trillion Suns in luminosity so they can be brighter than an entire galaxy and that's just coming from material around a fairly small region of space much smaller much much much smaller than an actual galaxy it's a very centers it's kind of just the galactic core now another interesting thing about quasars and this kind of gives credence to this notion of a constantly changing universe and even to some degree the Big Bang itself is you have these supermassive black holes that may be formed shortly after the Big Bang now you could imagine at an early stage in the universe's development there would been a lot of mass that didn't have that would have been near these black holes that didn't have quite the velocities to be able to escape them or be able to orbit around them and so these would actually start falling into the black hole and then over time all of the mass that had to fall into the black hole into the supermassive black hole will have fallen into the supermassive black hole and if you imagine some future period of time you should still have the supermassive black hole but all you should see is mostly things orbiting around it anything that had to fall into it would have already fallen into it so you you're just going to see things orbiting around it and this is actually what we see if we look around us we look at our Milky Way galaxy we don't observe a lot of things falling and we for example the Milky Way galaxy does does not have a does not does not have an active nucleus an active core it is not it is not currently a quasar the center of the Milky Way galaxy the supermassive black hole there is not I guess we could say digesting is not digesting or consuming material but you could imagine at some point in the Milky Way's past there might have been a lot of material that didn't have quite the velocity to be able to orbit and so that was consumed and as it would was consumed it would emit it would emit all of this x-ray radiation and could be observed as a quasar and that's actually what we observe the closest quasars and we've observed more than 200,000 quasars the closest quasars are on the order of 780 million million light years away light-years away so what does that mean we don't observe quasars closer 700 million light years so what that tells us is is at least in our region of the universe the most recent quasars were 700 million 780 million years in the past when we look at closer parts of the universe so I mean let me draw let's say this is the observable universe this is us so we only start to observe quasars at a certain distance away from us and that distance is actually also a certain time in the past because it took the light 780 million years to get to us and actually most of the quasars are more than three billion light years away which tells us that they only existed more than 3 billion years in the past at the at a younger stage of the actual universe when there was actual material for these supermassive black holes to consume at the center of galaxies you move closer in time to us and most of that material has actually been consumed and that's why and we just have material orbiting around these supermassive black holes which we call galaxies and so we don't observe quasars anymore and just to give an idea I mean you know these are as we everything we learn in cosmology there's kind of these mind-bending concepts unbelievable distances unbelievable masses unbelievable brightnesses I guess you could think about it but just to give a sense the brightest quasars the brightest known quasars devour on the order of 1,000 1,000 solar masses per year so that's on the order of 10 Earth's 10 earths per second if I did my math right 10 Earth's 10 Earth's 4 second are being devoured by the brightest quasars and it's that energy of that mass that's creating around it that's generating that's generating all of that energy and actually I should say I shouldn't even talk about in the present tense these brightest quasars this happened in the past we're just observing it now they're know as far all we know the rest of the universe looks fairly similar the way our universe does and so there really aren't that many quasars around although the other side of the coin might be even though most of the material has already been consumed maybe even by our own supermassive black call in the center of the Milky Way at some point in the future maybe it will be able to consume on some more stellar material some more a well any type of material in the future and that might happen about four or five billion years in the future when we actually collide with the Andromeda galaxy so anyway hopefully that gave you some food for thought