1 00:00:00,232 --> 00:00:01,867 What I wanna do in this video 2 00:00:01,867 --> 00:00:04,322 is talk a little bit about quasars. 3 00:00:06,153 --> 00:00:14,871 And that’s the short form for quasi-stellar radio sources. 4 00:00:16,733 --> 00:00:19,000 And this name is just a by-product 5 00:00:19,000 --> 00:00:20,867 of the first observations of quasars. 6 00:00:20,941 --> 00:00:24,000 Because all they’d look like were these kind of point-like 7 00:00:24,000 --> 00:00:29,489 sources of electromagnatic radiation, mainly in the radio part of the spectrum 8 00:00:29,489 --> 00:00:33,067 so that’s why we called them quasi-stellar radio sources. 9 00:00:33,067 --> 00:00:36,200 Now it turns out that they are neither stars 10 00:00:36,200 --> 00:00:38,067 or even quasi-stellar, and they’re actually not even— 11 00:00:38,067 --> 00:00:42,333 their main energy isn’t even being released in the radio frequency— 12 00:00:42,333 --> 00:00:45,232 in the radio band of the electromagnetic spectrum. 13 00:00:45,232 --> 00:00:47,600 They’re far more energetic than that. 14 00:00:47,600 --> 00:00:53,333 What they really are are the active nucleuses of galaxies. 15 00:00:53,333 --> 00:00:55,067 So let’s think about that a little bit. 16 00:00:55,067 --> 00:00:57,237 So if we have a supermassive black hole 17 00:00:57,237 --> 00:00:58,733 at the center of a galaxy. 18 00:00:58,733 --> 00:01:00,927 So let me draw that right over here. 19 00:01:00,927 --> 00:01:03,158 That’s our supermassive black hole. 20 00:01:03,158 --> 00:01:04,969 And maybe that’s the surface of the event horizon 21 00:01:04,969 --> 00:01:06,316 of the supermassive black hole 22 00:01:06,316 --> 00:01:11,467 The actual mass of the black hole is in the center of that event horizon. 23 00:01:11,467 --> 00:01:15,067 If there’s material that’s passing by this black hole 24 00:01:15,067 --> 00:01:16,667 it’s going to get attracted to it, 25 00:01:16,667 --> 00:01:19,067 and it’s going to form an accretion disk around it. 26 00:01:19,067 --> 00:01:23,067 This material is going to start rotating around this black hole 27 00:01:23,067 --> 00:01:25,333 and some of it, if it doesn’t have enough velocity, 28 00:01:25,333 --> 00:01:28,073 is going to actually fall into the black hole. 29 00:01:28,073 --> 00:01:30,933 So you have all of this material going around the black hole. 30 00:01:30,933 --> 00:01:33,739 And some of it, 31 00:01:33,739 --> 00:01:36,000 if it doesn’t have enough angular velocity, 32 00:01:36,000 --> 00:01:38,569 not enough to orbit around the black hole, 33 00:01:38,569 --> 00:01:40,467 it’s actually going to fall in. 34 00:01:40,467 --> 00:01:41,564 Now while things— 35 00:01:41,564 --> 00:01:44,795 let me label this; this is the accretion disk. 36 00:01:47,733 --> 00:01:51,267 So as things are getting faster and faster 37 00:01:51,267 --> 00:01:53,569 as they fall closer and closer to this black hole 38 00:01:53,569 --> 00:01:55,667 and bumping into each other more and more 39 00:01:55,667 --> 00:01:58,667 that gravitational potential energy from things falling into it 40 00:01:58,667 --> 00:02:01,069 is being turned into actual energy 41 00:02:01,069 --> 00:02:03,400 actual temperature 42 00:02:03,400 --> 00:02:07,333 so what you have is things start to get really, unbelievably 43 00:02:07,333 --> 00:02:10,867 unbelievably hot near the surface 44 00:02:13,236 --> 00:02:15,814 they get hotter and hotter as they fall closer and closer 45 00:02:15,814 --> 00:02:17,400 to that event horizon. 46 00:02:17,400 --> 00:02:19,320 And so near the event horizon itself, 47 00:02:19,320 --> 00:02:21,667 things are so intense that they’re actually releasing 48 00:02:21,667 --> 00:02:23,559 electromagnetic 49 00:02:23,559 --> 00:02:26,067 they’re actually releasing high-frequency 50 00:02:26,067 --> 00:02:27,493 electromagnetic radiation 51 00:02:27,493 --> 00:02:30,933 mainly in the x-ray part of the spectrum. 52 00:02:30,933 --> 00:02:32,723 Now I want to be very clear. 53 00:02:32,723 --> 00:02:34,467 So there’s two things here. 54 00:02:34,467 --> 00:02:38,244 One is, when you learn about quasars— 55 00:02:38,244 --> 00:02:40,318 or, when I was first exposed to quasars, 56 00:02:40,318 --> 00:02:41,667 in, like, a Nova special— 57 00:02:41,667 --> 00:02:44,933 they make you think that the radiation 58 00:02:44,933 --> 00:02:48,000 is somehow being released by the black hole itself 59 00:02:48,000 --> 00:02:50,200 and I would scratch my head. 60 00:02:50,200 --> 00:02:52,667 Because I was just told that nothing can escape 61 00:02:52,667 --> 00:02:54,150 the event horizon of a black hole, 62 00:02:54,150 --> 00:02:56,667 including electromagnetic radiation. 63 00:02:56,667 --> 00:02:59,133 So how could that be being emitted by the black hole? 64 00:02:59,133 --> 00:03:01,641 The answer is, it’s not being emitted by the black hole. 65 00:03:01,641 --> 00:03:04,552 It’s being emitted by the matter 66 00:03:04,552 --> 00:03:05,933 in the accretion disk 67 00:03:05,933 --> 00:03:09,067 that hasn’t quite gotten to the event horizon yet 68 00:03:09,067 --> 00:03:11,000 Once it’s inside of the event horizon, 69 00:03:11,000 --> 00:03:14,733 any electromagnetic radiation that it might emit 70 00:03:14,733 --> 00:03:17,880 will not be able to escape the black hole any more; 71 00:03:17,880 --> 00:03:20,600 will not be able to escape the actual event horizon. 72 00:03:20,600 --> 00:03:22,733 So all of this is from the accretion disk 73 00:03:22,733 --> 00:03:27,867 around the supermassive black hole. 74 00:03:27,867 --> 00:03:28,964 And the other question that used to 75 00:03:28,964 --> 00:03:30,108 pop in my mind 76 00:03:30,108 --> 00:03:33,833 is why does this kind of come out at these 77 00:03:33,833 --> 00:03:37,533 kind of perpendicular, kind of orthogonal to the plane 78 00:03:37,533 --> 00:03:40,629 of the actual accretion disk. 79 00:03:40,629 --> 00:03:43,400 At least my logic tells me, well things are not going to 80 00:03:43,400 --> 00:03:46,667 pop out along the direction of the accretion disk, 81 00:03:46,667 --> 00:03:48,800 because then they’re going to be absorbed by other things 82 00:03:48,800 --> 00:03:50,333 in fact that’s what’s going to cause other things 83 00:03:50,333 --> 00:03:51,642 to get heated up 84 00:03:51,642 --> 00:03:55,400 closer to the actual event horizon, 85 00:03:55,400 --> 00:03:58,133 so any energy that’s going out in that direction 86 00:03:58,133 --> 00:03:59,733 is just going to be absorbed 87 00:03:59,733 --> 00:04:01,200 and make other things hotter, 88 00:04:01,200 --> 00:04:03,600 and only when you go roughly perpendicular 89 00:04:03,600 --> 00:04:06,067 to the plane of the accretion disk 90 00:04:06,067 --> 00:04:10,800 is that energy aloud to kind of go transmit freely into space 91 00:04:10,800 --> 00:04:12,333 Now I want to be very clear: 92 00:04:12,333 --> 00:04:16,882 quasars are the most luminous things that we know of 93 00:04:16,882 --> 00:04:18,298 in the universe. 94 00:04:27,067 --> 00:04:30,133 The brightest, or actually, many quasars 95 00:04:30,133 --> 00:04:32,852 are on the order of a trillion suns in luminosity, 96 00:04:32,913 --> 00:04:35,467 so they can be brighter than an entire galaxy, 97 00:04:35,467 --> 00:04:39,231 and that’s just coming from material around a fairly small 98 00:04:39,231 --> 00:04:40,733 region of space, 99 00:04:40,733 --> 00:04:43,818 much, much, much smaller than an actual galaxy. 100 00:04:43,818 --> 00:04:47,000 It’s the very center, it’s kind of just the galactic core. 101 00:04:47,000 --> 00:04:50,333 Now another interesting thing about quasars 102 00:04:50,333 --> 00:04:52,153 and this kind of gives credence to this notion 103 00:04:52,153 --> 00:04:54,441 of a constantly changing universe, 104 00:04:54,441 --> 00:04:57,220 and even to some degree the Bing Bang itself, 105 00:04:57,220 --> 00:04:59,600 is you have these supermassive black holes 106 00:04:59,600 --> 00:05:02,200 that may be formed shortly after the Big Bang. 107 00:05:02,200 --> 00:05:04,733 Now you can imagine, at an early stage 108 00:05:04,733 --> 00:05:06,387 in the universe’s development, 109 00:05:06,387 --> 00:05:09,313 there would’ve been a lot of mass that would’ve been near 110 00:05:09,313 --> 00:05:12,333 these black holes that didn’t have quite the velocities 111 00:05:12,333 --> 00:05:14,667 to be able to escape them or be able to orbit around them, 112 00:05:14,667 --> 00:05:18,800 and so these would actually start falling into the black hole. 113 00:05:18,800 --> 00:05:20,067 And then, over time, all of the mass 114 00:05:20,067 --> 00:05:23,533 that had to fall into the black hole, the supermassive black hole 115 00:05:23,533 --> 00:05:26,067 will have fallen into the supermassive black hole, 116 00:05:26,067 --> 00:05:27,819 and if you imagine some future period of time, 117 00:05:27,819 --> 00:05:31,333 you should still have the supermassive black hole, 118 00:05:31,333 --> 00:05:34,667 but all you should see is mostly things orbiting around it. 119 00:05:34,667 --> 00:05:36,133 Anything that had to fall into it 120 00:05:36,133 --> 00:05:38,600 would’ve already fallen into it. 121 00:05:38,600 --> 00:05:41,566 So you’re just going to see things orbiting around it. 122 00:05:41,566 --> 00:05:43,067 And this is actually what we see. 123 00:05:43,067 --> 00:05:44,667 If we look around us. If we look at our Milky Way Galaxy. 124 00:05:44,667 --> 00:05:47,400 We don’t observe a lot of things falling in. 125 00:05:47,400 --> 00:05:54,151 For example, the Milky Way does not have an active nucleus. 126 00:05:54,151 --> 00:05:55,637 An active core. 127 00:05:55,637 --> 00:05:58,067 It is not currently a quasar, 128 00:05:58,067 --> 00:05:59,667 the center of the Milky Way Galaxy. 129 00:05:59,667 --> 00:06:01,267 The supermassive black hole there 130 00:06:01,267 --> 00:06:04,133 is not, I guess we could say, is not digesting 131 00:06:04,133 --> 00:06:06,933 or consuming material. 132 00:06:06,933 --> 00:06:09,800 But you could imagine that sometime in the Milky Way’s past 133 00:06:09,800 --> 00:06:12,634 there might’ve been a lot of material that didn’t have 134 00:06:12,634 --> 00:06:16,303 quite the velocity to be able to orbit, and so that was consumed, 135 00:06:16,303 --> 00:06:19,667 and when it was consumed, it would emit 136 00:06:19,667 --> 00:06:24,733 all of this x-ray radiation, and could be observed as a quasar. 137 00:06:24,733 --> 00:06:26,667 And that’s actually what we observe. 138 00:06:26,667 --> 00:06:28,723 The closest quasars, and we’ve observed more 139 00:06:28,723 --> 00:06:30,885 than 200,000 quasars. 140 00:06:30,885 --> 00:06:33,133 The closest quasars are on the order of 141 00:06:33,133 --> 00:06:39,667 780 million—million!—light-years away. 142 00:06:39,667 --> 00:06:40,567 So what does that mean? 143 00:06:40,567 --> 00:06:43,667 We don’t observe quasars closer than 700 million light-years 144 00:06:43,667 --> 00:06:48,400 So what that tells us is, at least in our region of the universe 145 00:06:48,400 --> 00:06:54,267 the most recent quasars were 780 million years in the past. 146 00:06:54,267 --> 00:06:56,867 When we look at closer parts of the universe— 147 00:06:56,867 --> 00:06:58,133 so let me draw— 148 00:06:58,133 --> 00:07:01,333 let’s say this is the observable universe; this is us— 149 00:07:01,333 --> 00:07:03,600 so we only start to observe quasars 150 00:07:03,600 --> 00:07:05,552 at a certain distance away from us, 151 00:07:05,552 --> 00:07:08,933 and this distance is actually at a certain time in the past. 152 00:07:08,933 --> 00:07:11,333 because it took the light 780 million years to get to us. 153 00:07:11,333 --> 00:07:16,000 And most of the quasars are more than 3 billion light years away, 154 00:07:16,000 --> 00:07:18,133 which tells us that they only existed more than 155 00:07:18,133 --> 00:07:23,533 3 billion years in the past, at a younger stage 156 00:07:23,533 --> 00:07:25,467 of the actual universe, 157 00:07:25,467 --> 00:07:27,890 when there was actual material for these 158 00:07:27,890 --> 00:07:30,333 supermassive black holes to consume 159 00:07:30,333 --> 00:07:31,638 at the center of galaxies. 160 00:07:31,638 --> 00:07:34,733 As you move closer in time to us, and most of that material 161 00:07:34,733 --> 00:07:36,737 has actually been consumed. 162 00:07:36,737 --> 00:07:39,267 And we just have material orbiting around 163 00:07:39,267 --> 00:07:40,986 these supermassive black holes, 164 00:07:40,986 --> 00:07:42,652 which we call galaxies, 165 00:07:42,652 --> 00:07:45,333 and so we don’t observe quasars anymore. 166 00:07:45,333 --> 00:07:46,800 And just to give an idea— 167 00:07:46,800 --> 00:07:48,933 I mean, you know, as with everything we learn in cosmology, 168 00:07:48,933 --> 00:07:50,933 there’s kind of these mind-bending concepts, 169 00:07:50,933 --> 00:07:54,639 unbelievable distances, unbelievable masses, 170 00:07:54,639 --> 00:07:57,400 unbelievable brightnesses, I guess you could think about it, 171 00:07:57,400 --> 00:08:01,333 but just to give a sense, the brightest known quasars 172 00:08:01,333 --> 00:08:11,533 devour on the order of 1000 solar masses per year. 173 00:08:11,533 --> 00:08:16,837 So that’s on the order of 10 earths per second, 174 00:08:16,837 --> 00:08:18,467 if I did my math right. 175 00:08:18,467 --> 00:08:25,916 Ten earths per second are being devoured by the brightest quasars. 176 00:08:25,916 --> 00:08:27,823 And it’s that energy of that mass 177 00:08:27,823 --> 00:08:30,003 that’s accreting around it that’s generating 178 00:08:30,003 --> 00:08:33,467 that’s generating all of that energy. 179 00:08:33,467 --> 00:08:34,698 And actually I should say, 180 00:08:34,698 --> 00:08:36,050 I shouldn’t even talk about it in the present tense. 181 00:08:36,050 --> 00:08:38,249 These brightest quasars, this happened in the past, 182 00:08:38,249 --> 00:08:39,702 we’re just observing it now. 183 00:08:39,702 --> 00:08:41,687 There are no—as—for all we know, 184 00:08:41,687 --> 00:08:43,446 the rest of the universe looks fairly similar 185 00:08:43,446 --> 00:08:45,015 to the way our universe does, 186 00:08:45,015 --> 00:08:47,400 so there really aren’t that many quasars around. 187 00:08:47,400 --> 00:08:50,019 Although you know, the other side of the coin might be 188 00:08:50,019 --> 00:08:52,689 even though most of the material has already been consumed, 189 00:08:52,689 --> 00:08:54,585 maybe even by our own supermassive black hole 190 00:08:54,585 --> 00:08:56,995 in the center of the Milky Way, 191 00:08:56,995 --> 00:09:00,333 at some point in the future, maybe it will be able to consume 192 00:09:00,333 --> 00:09:05,067 on some more stellar material, some more, well, 193 00:09:05,067 --> 00:09:06,533 any type of material in the future, 194 00:09:06,533 --> 00:09:09,200 and that might happen about 4, 5 billion years in the future 195 00:09:09,200 --> 00:09:11,933 when we actually collide with the Andromeda Galaxy. 196 00:09:11,933 --> 99:59:59,999 So, anyway, hopefully that gave you some food for thought.