WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.839 slumber under the night sky. 7 00:00:26.879 --> 00:00:29.160 I want you to imagine, just for a second, that 8 00:00:29.239 --> 00:00:32.039 you're standing on a beach and you're staring out at 9 00:00:32.039 --> 00:00:34.119 this vast, churning ocean. 10 00:00:34.200 --> 00:00:35.439 Okay, I'm picturing it. 11 00:00:35.439 --> 00:00:38.320 Right, But there's a catch. You can't actually see the 12 00:00:38.359 --> 00:00:39.719 water like at all. 13 00:00:39.920 --> 00:00:40.119 Wow. 14 00:00:40.200 --> 00:00:42.759 Yeah, the ocean is completely invisible. The only thing you 15 00:00:42.759 --> 00:00:46.719 can actually see is the sea foam right on the surface, 16 00:00:47.000 --> 00:00:48.280 just floating there in midair. 17 00:00:48.399 --> 00:00:52.039 That is a deeply unsettling mental image, I know. 18 00:00:52.119 --> 00:00:55.200 Right, But that's essentially the reality of the universe you're 19 00:00:55.200 --> 00:00:58.159 sitting in right now. Like everything you can see, your hands, 20 00:00:58.159 --> 00:01:00.600 the room, you're in, the stars, and the night sky, 21 00:01:01.159 --> 00:01:02.439 that's just the sea foam. 22 00:01:02.520 --> 00:01:05.000 The visible debris, exactly. 23 00:01:04.719 --> 00:01:08.400 The visible debris. And today we're going to talk about 24 00:01:08.760 --> 00:01:13.319 the invisible ocean, the dark matter, and more importantly, what 25 00:01:13.400 --> 00:01:16.239 happens when the most extreme objects in the universe violently 26 00:01:16.280 --> 00:01:18.439 collide inside that invisible ocean. 27 00:01:18.719 --> 00:01:22.079 And honestly, the methodology we're looking at today is it's 28 00:01:22.159 --> 00:01:24.519 just a brilliant shift in how we approach this. 29 00:01:24.719 --> 00:01:26.599 It really is. I mean, we're talking about a completely 30 00:01:26.640 --> 00:01:28.560 new way of looking at data we already. 31 00:01:28.280 --> 00:01:32.799 Have, right because for decades the astrophysics community has been 32 00:01:32.840 --> 00:01:37.079 trying to build these massive, ultra sensitive particle detectors to 33 00:01:37.159 --> 00:01:38.239 catch dark matter. 34 00:01:38.120 --> 00:01:40.439 And catching exactly zero particles. 35 00:01:40.159 --> 00:01:43.439 Right, pretty much. Yeah, But this new framework developed by 36 00:01:43.439 --> 00:01:49.079 this incredible coalition of physicists from MIT, Eucluvane, University of Amsterdam, 37 00:01:49.359 --> 00:01:55.120 Queen Mary University, and Oxford, it completely discards. 38 00:01:54.640 --> 00:01:56.319 The particle detector, which is wild. 39 00:01:56.560 --> 00:02:00.560 It is they are using gravitational waves, the literal ripples 40 00:02:00.560 --> 00:02:03.200 in the fabric of space and time to feel the 41 00:02:03.280 --> 00:02:04.719 drag of dark matter. 42 00:02:04.519 --> 00:02:06.159 Which just sounds like pure science fiction. 43 00:02:06.359 --> 00:02:08.560 It does, but it's happening, and the elegance of it 44 00:02:08.599 --> 00:02:11.719 lies in the math. It's a highly sophisticated way of 45 00:02:11.759 --> 00:02:15.240 predicting how the most extreme gravitational environments in the universe 46 00:02:15.479 --> 00:02:16.840 interact with the dark sector. 47 00:02:16.879 --> 00:02:18.919 Okay, so let's unpack this, Yeah, because I want to 48 00:02:18.919 --> 00:02:20.439 make sure we're all on the same page before we 49 00:02:20.479 --> 00:02:23.400 get to colliding black holes. It is. So, we have 50 00:02:23.479 --> 00:02:27.080 this dark matter, and the accepted number is that it 51 00:02:27.120 --> 00:02:29.120 makes up something like eighty five percent of all the 52 00:02:29.120 --> 00:02:30.240 matter in the universe. 53 00:02:30.000 --> 00:02:31.719 Right right, roughly eighty five percent. 54 00:02:31.919 --> 00:02:33.879 Okay, But if I'm playing Devil's advocate here, if this 55 00:02:33.919 --> 00:02:38.199 stuff is completely invisible, if it totally ignores light passes 56 00:02:38.280 --> 00:02:41.719 right through magnets, passes through the Earth, passes through us, 57 00:02:41.960 --> 00:02:47.159 how on Earth are physicists so incredibly confident that it's 58 00:02:47.199 --> 00:02:48.560 eighty five percent of everything. 59 00:02:48.599 --> 00:02:51.120 Well, what's fascinating here is that the universe gives us 60 00:02:51.199 --> 00:02:54.360 a scale that we just can't ignore. We can't see it, 61 00:02:54.400 --> 00:02:56.199 but we can definitely feel its weight. 62 00:02:56.520 --> 00:02:59.000 Like a ghost in a haunted house. Uh kind of Yeah, 63 00:02:59.120 --> 00:03:00.919 you can't see the ghost walking through the wall, but 64 00:03:00.960 --> 00:03:03.280 you hear the floorboards creaking under its boots. 65 00:03:03.560 --> 00:03:06.680 That's actually, that's a really good analogy. The creaking floorboards 66 00:03:06.680 --> 00:03:09.560 in this case is gravity, right. Gravity is our only 67 00:03:09.599 --> 00:03:12.639 tool to catch it right now. So when astronomers look 68 00:03:12.680 --> 00:03:17.919 at say, distant galaxies, they see the light from those galaxies. 69 00:03:17.360 --> 00:03:19.639 Bend standing around something in the foreground. 70 00:03:19.240 --> 00:03:24.120 Exactly, bending around massive invisible structures. We call this gravitational 71 00:03:24.199 --> 00:03:25.280 lensing because. 72 00:03:25.000 --> 00:03:26.879 The gravity is literally acting like. 73 00:03:26.840 --> 00:03:31.759 A glass lens precisely. General relativity tells us that mass 74 00:03:32.000 --> 00:03:35.520 bends space time. So when light from a distant galaxy 75 00:03:35.639 --> 00:03:38.840 travels past a massive object, it's path. 76 00:03:38.639 --> 00:03:40.520 Curves, and we can measure that curve. 77 00:03:40.759 --> 00:03:43.680 We can, And when we calculate the mass required to 78 00:03:43.719 --> 00:03:45.439 bend the light that much, and then we add up 79 00:03:45.439 --> 00:03:48.479 all the visible stars and gas in that area, the 80 00:03:48.520 --> 00:03:50.039 math just doesn't work. 81 00:03:50.120 --> 00:03:52.759 There's not an invisible stuff, not even close. 82 00:03:52.919 --> 00:03:55.840 There has to be a massive invisible force pulling on 83 00:03:55.960 --> 00:03:59.080 that light, and it has to be huge, Hence the 84 00:03:59.280 --> 00:03:59.879 eighty five. 85 00:04:00.879 --> 00:04:03.199 Okay, so we know the ghost is heavy, we know 86 00:04:03.240 --> 00:04:07.080 it's there, right, But the astrophysics community has been chasing 87 00:04:07.280 --> 00:04:09.879 a very specific kind of ghost for a long time, 88 00:04:09.960 --> 00:04:12.159 haven't they, Like the wimp. 89 00:04:12.400 --> 00:04:15.879 Yes, the weekly interacting Massive particle WHIMS have been the 90 00:04:15.919 --> 00:04:17.680 favored candidate for decades. 91 00:04:17.720 --> 00:04:20.839 But this new research, the MIT team, they're pivoting away 92 00:04:20.839 --> 00:04:23.079 from WHIMS completely, right. Yeah, they're looking at something called 93 00:04:23.079 --> 00:04:24.639 a light scaler particle. 94 00:04:24.319 --> 00:04:28.000 They are, Yeah, and that pivot is largely driven by well. 95 00:04:27.959 --> 00:04:30.920 Frustration, frustration with the empty particle detector. 96 00:04:31.040 --> 00:04:34.439 Exactly. We've built these incredibly sensitive underground vats filled with 97 00:04:34.519 --> 00:04:35.600 liquid xenon. 98 00:04:35.800 --> 00:04:39.560 Deep underground to shield them from cosmic rays and stuff, right. 99 00:04:39.680 --> 00:04:42.279 And we wait for a massive wimp to just bump 100 00:04:42.279 --> 00:04:45.519 into a xenon nucleus and produce the tiny flash of light. 101 00:04:45.759 --> 00:04:47.399 But no flashes, no flashes. 102 00:04:47.680 --> 00:04:52.839 The detectors are remarkably quiet. So theoretical physics has to adapt. 103 00:04:53.480 --> 00:04:57.360 We have to explore other candidates that still fit the 104 00:04:57.399 --> 00:05:02.040 macroscopic gravity data, the lensing, the alexy rotation, but maybe 105 00:05:02.040 --> 00:05:04.120 behave totally differently on a quantum level. 106 00:05:04.319 --> 00:05:06.000 Enter the light scalar particle. 107 00:05:05.759 --> 00:05:08.759 Enter the light scaler. So, in quantum mechanics, particles have 108 00:05:08.839 --> 00:05:12.759 this property called spin, its intrinsic angular momentum. 109 00:05:12.839 --> 00:05:14.399 Right, like an electron has a half spin. 110 00:05:14.600 --> 00:05:17.680 Yes, photons have a spin of one, but a scaler 111 00:05:17.720 --> 00:05:20.199 particle has a spin of exactly zero Okay. 112 00:05:20.120 --> 00:05:22.439 Meaning it doesn't have a built in direction exactly. 113 00:05:22.600 --> 00:05:25.040 The only fundamental scalar particle we've ever found is. 114 00:05:25.000 --> 00:05:27.800 The Higgs boson, which gives mass to everything. 115 00:05:27.959 --> 00:05:31.079 Right, But the crucial variable here isn't just the zero spin. 116 00:05:31.279 --> 00:05:32.839 It's the prefix light. 117 00:05:32.959 --> 00:05:36.360 Because they are incredibly, almost incomprehensibly light. 118 00:05:36.439 --> 00:05:40.279 We are talking billions of times lighter than a single electron, 119 00:05:40.680 --> 00:05:42.839 down to fractions of an electron volt. 120 00:05:42.959 --> 00:05:46.480 Okay, wait, if they are that small, how do they 121 00:05:46.480 --> 00:05:50.079 make up eighty five percent of the universe. There must 122 00:05:50.120 --> 00:05:52.519 be an unfathomable number of them there are. 123 00:05:52.759 --> 00:05:56.920 And what's fascinating here is how ultra light masses force 124 00:05:57.040 --> 00:06:01.040 us to confront wave particle durality at an aca strophysical scale. 125 00:06:01.120 --> 00:06:03.720 Oh boy, okay, quantum mechanics on a massive scale. 126 00:06:03.800 --> 00:06:07.319 Right. Because of quantum mechanics, every particle has a wavelength 127 00:06:07.399 --> 00:06:12.040 of de Brogli wavelength. Sure, heavy particles have tiny wavelengths, 128 00:06:12.160 --> 00:06:15.600 so they act like little localized billiard balls. But if 129 00:06:15.639 --> 00:06:18.399 you take a particle that is absurdly light, like ten 130 00:06:18.439 --> 00:06:22.560 to the minus ten electron volts, its quantum wavelength stretches 131 00:06:22.600 --> 00:06:24.199 out immensely. 132 00:06:23.720 --> 00:06:25.600 How immensely like across a room. 133 00:06:25.720 --> 00:06:29.079 We're talking meters, kilometers, maybe even astronomical distances. 134 00:06:29.199 --> 00:06:33.040 Wait, a single particle's quantum field stretches for kilometers exactly. 135 00:06:33.079 --> 00:06:35.759 And because these are scalar bosons, they don't obey the 136 00:06:35.800 --> 00:06:37.720 poly exclusion principle. 137 00:06:37.360 --> 00:06:38.959 Meaning they can share the same space. 138 00:06:39.079 --> 00:06:41.240 Right, you can pack an infinite number of them into 139 00:06:41.279 --> 00:06:42.199 the exact same. 140 00:06:42.079 --> 00:06:44.439 Quantum state, so they just stack on top of each other. 141 00:06:44.600 --> 00:06:47.759 They overlap perfectly, so instead of a bunch of individual 142 00:06:47.800 --> 00:06:51.519 discrete particles bouncing around like ping pong balls, they form 143 00:06:51.560 --> 00:06:56.600 this macroscopic quantum state they behave as a single cohesive 144 00:06:57.079 --> 00:06:58.120 oscillating wave. 145 00:06:58.680 --> 00:07:01.800 Okay, so our ghost isn't a swarm of bugs. It's 146 00:07:01.839 --> 00:07:03.800 more like a thick, undulating fog. 147 00:07:04.040 --> 00:07:06.079 That's a great way to look at it, a cohesive 148 00:07:06.160 --> 00:07:10.680 classical field, and that fundamentally changes the game for how 149 00:07:10.680 --> 00:07:11.800 we try to detect it. 150 00:07:11.879 --> 00:07:13.600 Right, because a fog isn't going to bump into a 151 00:07:13.680 --> 00:07:16.480 single xenon atom in an underground tank and make a 152 00:07:16.519 --> 00:07:19.319 fly exactly. We need something way bigger. We need to 153 00:07:19.360 --> 00:07:22.600 see how that massive fog interacts with the biggest, heaviest 154 00:07:22.600 --> 00:07:24.920 things in the universe, which brings us to. 155 00:07:24.920 --> 00:07:27.480 Black holes see Ultimate gravitational engines. 156 00:07:27.600 --> 00:07:30.759 Right, And the researchers describe this interaction, this fog hitting 157 00:07:30.959 --> 00:07:34.920 a rapidly spinning black hole as something called super radiance. Yes, 158 00:07:35.600 --> 00:07:37.680 and the analogy that you use in the research is 159 00:07:38.240 --> 00:07:41.720 it's akin to turning cream into butter, which I love. 160 00:07:41.879 --> 00:07:43.560 It's very evocative, it is. 161 00:07:43.879 --> 00:07:46.480 But here's where it gets really interesting for me, because 162 00:07:46.480 --> 00:07:48.480 I mean, we usually think of blank holes as these 163 00:07:48.560 --> 00:07:50.519 ultimate vacuum cleaners, right right. 164 00:07:50.360 --> 00:07:51.879 The classic pop science view. 165 00:07:52.160 --> 00:07:55.959 Nothing of STAPs exactly. They just consume everything. So how 166 00:07:56.079 --> 00:07:59.279 on Earth is a black hole acting like a butter churn? 167 00:08:00.480 --> 00:08:04.319 How is it transferring its energy outward to amplify this 168 00:08:04.439 --> 00:08:05.399 dark matter fog. 169 00:08:05.600 --> 00:08:08.399 To understand that, we have to look at the geometry 170 00:08:08.600 --> 00:08:12.519 of a spinning black hole. Okay, it's described mathematically by 171 00:08:12.560 --> 00:08:15.360 the Cerr metric. So a spinning black hole doesn't just 172 00:08:15.399 --> 00:08:18.000 have an event horizon the point of no return, it 173 00:08:18.040 --> 00:08:21.560 also has this region just outside the horizon called the ergosphere. 174 00:08:21.600 --> 00:08:25.040 The ergosphere sounds intense. It is intense because the black 175 00:08:25.079 --> 00:08:28.360 hole is so massive and it's rotating so incredibly fast, 176 00:08:28.839 --> 00:08:31.920 it physically drags the fabric of space time along with. 177 00:08:31.839 --> 00:08:34.120 It, like a spoon stirring thick syrup. 178 00:08:34.200 --> 00:08:37.639 Precisely, that's called frame dragging, and inside the ergosphere, space 179 00:08:37.679 --> 00:08:40.159 time is being dragged around the black hole so violently 180 00:08:40.200 --> 00:08:42.279 that it's literally moving faster than the speed of light. 181 00:08:42.399 --> 00:08:44.559 Faster than light just the space itself right. 182 00:08:44.440 --> 00:08:47.679 Relative to an observer far away. So in that region 183 00:08:47.799 --> 00:08:50.639 it's physically impossible for anything to stand still. Everything has 184 00:08:50.639 --> 00:08:53.519 to co rotate with the black hole. Wow. Okay, so 185 00:08:53.559 --> 00:08:57.080 our dark matter wave, this scaler fog gets drawn into 186 00:08:57.080 --> 00:09:00.559 the gravitational well, yes, it enters the ergosphere that's forced 187 00:09:00.559 --> 00:09:01.600 to spin exactly. 188 00:09:02.080 --> 00:09:04.120 But just getting dragged in a circle doesn't mean the 189 00:09:04.120 --> 00:09:05.039 wave gains. 190 00:09:04.840 --> 00:09:07.120 Energy, right, it's just a long for the ride. 191 00:09:07.200 --> 00:09:10.399 For energy to transfer, we need an extraction mechanism, and 192 00:09:10.440 --> 00:09:12.559 that happens through a wave scattering process. 193 00:09:12.639 --> 00:09:13.759 Okay, break that down for me. 194 00:09:13.919 --> 00:09:17.080 When the incoming scaler wave scatters off the black hole, 195 00:09:17.480 --> 00:09:21.399 a really weird mathematical boundary condition pops up. If the 196 00:09:21.440 --> 00:09:24.559 wave is rotating slower than the black hole itself, the 197 00:09:24.600 --> 00:09:25.360 wave split. 198 00:09:25.519 --> 00:09:26.159 It splits. 199 00:09:26.279 --> 00:09:29.360 Yeah, a portion of the wave falls into the event horizon. 200 00:09:29.600 --> 00:09:32.639 It's gone, okay, standard black hole behavior. 201 00:09:32.879 --> 00:09:36.559 But because of the extreme physics in the ergosphere, that 202 00:09:36.720 --> 00:09:40.000 infalling piece of the wave can actually have negative energy. 203 00:09:40.080 --> 00:09:42.000 Wait, hold on, negative energy. 204 00:09:41.759 --> 00:09:43.120 Relative to the outside universe. 205 00:09:43.200 --> 00:09:45.919 Yees, Okay, let me just unpack the conservation of energy here. 206 00:09:46.440 --> 00:09:50.679 If the black hole absorbs a wave packet with negative energy. 207 00:09:51.159 --> 00:09:54.960 Then the black hole's overall mass and its rotational energy 208 00:09:55.000 --> 00:09:55.559 have to go down. 209 00:09:55.679 --> 00:09:58.480 Right, Yes, the black hole slows down a tiny. 210 00:09:58.200 --> 00:10:02.039 Bit so to balance the cause Ledger, the piece of 211 00:10:02.080 --> 00:10:04.519 the wave that bounces off, the part that scatters away, 212 00:10:05.159 --> 00:10:08.240 has to emerge with more energy than it started with. 213 00:10:08.519 --> 00:10:12.639 The math demands it. The outgoing wave is amplified. It 214 00:10:12.799 --> 00:10:15.600 literally steals rotational energy from the black hole. 215 00:10:15.720 --> 00:10:16.559 That is mind blowing. 216 00:10:16.679 --> 00:10:19.799 It gets better. Here is where the butter churn analogy 217 00:10:20.000 --> 00:10:20.720 really shines. 218 00:10:20.879 --> 00:10:21.480 Okay, hit me. 219 00:10:21.799 --> 00:10:24.240 The wave doesn't just scatter once and fly off into 220 00:10:24.240 --> 00:10:28.240 deep space. The black hole's gravity creates a potential well. 221 00:10:28.840 --> 00:10:31.320 It traps the wave like an orbit, kind of like 222 00:10:31.320 --> 00:10:34.279 how a proton traps an electron in an atom. So 223 00:10:34.559 --> 00:10:38.759 this amplified dark matter wave is stuck. It bounces back 224 00:10:38.799 --> 00:10:42.480 and forth in this gravity well, repeatedly passing through the ergosphere, 225 00:10:43.120 --> 00:10:46.559 and every single time it passes through it extracts more energy. 226 00:10:46.639 --> 00:10:50.559 It gets amplified again. It's exponential. It is a runaway 227 00:10:50.639 --> 00:10:54.159 exponential amplification. The black hole is just dumping its spin 228 00:10:54.279 --> 00:10:56.679 energy into the surrounding dark matter, whipping it up, making 229 00:10:56.679 --> 00:10:58.159 it incredibly. 230 00:10:57.519 --> 00:10:59.360 Dense, turning the cream into butter. 231 00:10:59.279 --> 00:11:01.279 Exactly until it saturates. 232 00:11:01.360 --> 00:11:03.000 When does it saturate, usually. 233 00:11:02.799 --> 00:11:04.759 When the black hole has spun down so much that 234 00:11:04.799 --> 00:11:08.440 it's no longer spinning faster than the wave. At that point, 235 00:11:08.480 --> 00:11:11.799 you're left with what physicists call a bosonic cloud. 236 00:11:11.919 --> 00:11:14.879 A bosonic cloud. Yeah, so instead of just a diffuse 237 00:11:14.879 --> 00:11:19.799 invisible fog, we now have a highly concentrated, super dense 238 00:11:19.840 --> 00:11:23.919 halo of dark matter tightly bound to this black hole. 239 00:11:24.039 --> 00:11:27.279 Orders of magnitude denser than the ambient dark matter in 240 00:11:27.320 --> 00:11:28.000 the galaxy. 241 00:11:28.320 --> 00:11:31.200 Wow. Okay, so that is the setup. That's the trap 242 00:11:31.200 --> 00:11:32.720 we're setting for the ghost, right. 243 00:11:32.960 --> 00:11:35.639 But there's a problem. There usually is a single black 244 00:11:35.679 --> 00:11:38.320 hole just sitting there in space with its dense little 245 00:11:38.399 --> 00:11:42.399 dark matter cloud. It doesn't really emit gravitational waves, at 246 00:11:42.440 --> 00:11:44.879 least not ones we can easily detect from Earth. 247 00:11:44.960 --> 00:11:45.759 It's too quiet. 248 00:11:45.840 --> 00:11:48.000 It's too quiet to trigger our detectors. You need a 249 00:11:48.039 --> 00:11:50.879 massive perturbation, you need a cataclysm. 250 00:11:50.279 --> 00:11:53.440 You need a binary system, two black holes crashing into 251 00:11:53.519 --> 00:11:53.840 each other. 252 00:11:54.039 --> 00:11:54.279 Yes. 253 00:11:54.480 --> 00:11:57.360 So this MIT and European team, they set out to 254 00:11:57.399 --> 00:12:00.799 build a predigative model to figure out exactly what it 255 00:12:00.840 --> 00:12:03.519 looks like when two black holes merge, but one of 256 00:12:03.559 --> 00:12:05.440 them or both of them is wrapped in this thick, 257 00:12:05.720 --> 00:12:07.159 heavy butter of dark matter. 258 00:12:07.360 --> 00:12:09.519 And that is not a trivial task I can imagine. 259 00:12:09.559 --> 00:12:12.519 I mean, Einstein's equations are brutal on a good day. 260 00:12:12.399 --> 00:12:18.120 Right, highly complex nonlinear coupled partial differential equations. If we 261 00:12:18.159 --> 00:12:22.519 connect this to the bigger picture of computational astrophysics, just 262 00:12:22.799 --> 00:12:26.840 simulating two black holes colliding in a total vacuum empty 263 00:12:26.879 --> 00:12:32.399 space that took physicists decades to solve. Wait, really decades, decades. 264 00:12:32.799 --> 00:12:36.480 The breakthrough in numerical relativity only happened around two thousand 265 00:12:36.480 --> 00:12:38.679 and five, just to do it in empty space exactly. 266 00:12:38.759 --> 00:12:42.600 So now imagine adding a massive dynamic sloshing cloud of 267 00:12:42.679 --> 00:12:44.440 Scaler particles to that simulation. 268 00:12:44.559 --> 00:12:45.720 The math must be a nightmare. 269 00:12:45.840 --> 00:12:49.799 It introduces immense computational complexity. You have to track the 270 00:12:49.799 --> 00:12:52.159 gravity of the black holes, the rippling of the space 271 00:12:52.200 --> 00:12:54.919 time metric, and the gravitational pull of the dark matter 272 00:12:54.960 --> 00:12:56.240 pulling back on the black holes. 273 00:12:56.559 --> 00:12:58.960 Right, because the dark matter has mass, so it's going 274 00:12:59.000 --> 00:12:59.879 to exert drag. 275 00:13:00.080 --> 00:13:01.440 We call it dynamical friction. 276 00:13:01.639 --> 00:13:04.240 Diamical friction, so paint me a picture. How does that 277 00:13:04.320 --> 00:13:07.559 drag actually play out as they spiral in towards each other. 278 00:13:07.919 --> 00:13:11.399 So imagine the secondary black hole plunging through the dark 279 00:13:11.440 --> 00:13:14.840 matter cloud of the primary black hole. As it moves, 280 00:13:14.919 --> 00:13:17.000 its gravity pulls the dark matter. 281 00:13:16.840 --> 00:13:19.480 Particles toward it, okay, kind of sweeping them up. 282 00:13:19.600 --> 00:13:21.519 Not quite sweeping them up, but pulling them in so 283 00:13:21.600 --> 00:13:25.480 they bunch up behind it. It creates a gravitational. 284 00:13:24.879 --> 00:13:27.120 Wake like a boat moving through water. 285 00:13:27.360 --> 00:13:30.799 Yes, an area of higher density trailing right behind the 286 00:13:30.840 --> 00:13:34.720 moving black hole. And because that wake has mass, its 287 00:13:34.720 --> 00:13:36.919 gravity pulls backward on the black hole. 288 00:13:37.080 --> 00:13:40.279 Oh wow, it's literally putting the brakes on exactly. 289 00:13:40.320 --> 00:13:43.559 It bleeds away the black hole's orbital energy and that 290 00:13:43.639 --> 00:13:47.960 fundamentally alters the merger. Oh so well. In a vacuum, 291 00:13:48.360 --> 00:13:52.399 two black holes only lose energy by emitting gravitational waves. 292 00:13:52.799 --> 00:13:56.799 They spiral inward at a very predictable smooth rate. It 293 00:13:56.840 --> 00:13:58.720 produces a signal we call a chirp. 294 00:13:58.799 --> 00:14:01.840 The chirp because the frequency and the amplitude go up 295 00:14:01.879 --> 00:14:03.240 smoothly until they collide. 296 00:14:03.320 --> 00:14:07.080 Right. But when you add dynamical friction from the basonic cloud, 297 00:14:07.200 --> 00:14:10.039 they are losing energy through an extra channel for a drag. Yes, 298 00:14:10.320 --> 00:14:13.159 so they spiral inward faster than they normally would. The 299 00:14:13.320 --> 00:14:15.919 orbital trajectory tightens much faster, so. 300 00:14:15.919 --> 00:14:21.039 The phase of the gravitational wave changes, the chirp is accelerated. 301 00:14:20.440 --> 00:14:23.559 The frequency increases more rapidly. Yes, And it's even more 302 00:14:23.559 --> 00:14:26.600 complicated because the secondary black hole isn't just orbiting the 303 00:14:26.600 --> 00:14:30.279 primary black hole anymore. It's orbiting the combined mass of 304 00:14:30.279 --> 00:14:32.840 the black hole and the dark matter cloud. 305 00:14:33.159 --> 00:14:35.440 So the team had to use supercomputers to solve all 306 00:14:35.440 --> 00:14:35.639 of this. 307 00:14:35.879 --> 00:14:39.600 Yes, they solve the Einstein Klan Gordon equations. 308 00:14:39.240 --> 00:14:42.720 Just casually solving the Einstein Clan Gordon equations as you do. 309 00:14:42.799 --> 00:14:46.279 Right, which govern the scaler field in curved space time. 310 00:14:47.039 --> 00:14:51.200 They ran all these simulations to generate theoretical waveforms, a 311 00:14:51.360 --> 00:14:52.799 vast library of them. 312 00:14:52.879 --> 00:14:54.879 Basically, they built a dictionary. 313 00:14:54.440 --> 00:14:57.200 A dictionary of what a dark matter merger should look like. 314 00:14:57.399 --> 00:15:00.879 They tweets the masses, the density of the cloud, the 315 00:15:00.879 --> 00:15:02.399 mass of the scaler particles. 316 00:15:02.559 --> 00:15:05.600 Okay, so what does this all mean for us on Earth? 317 00:15:05.679 --> 00:15:08.200 I mean, they have this theoretical dictionary, but how do 318 00:15:08.240 --> 00:15:08.799 you test it? 319 00:15:09.159 --> 00:15:11.679 You turn to the actual data. The public archives of 320 00:15:11.720 --> 00:15:14.039 the Lego Virgo Caagra network. 321 00:15:13.679 --> 00:15:16.919 The LVK network, which, for anyone who doesn't know, is 322 00:15:17.080 --> 00:15:20.919 just a global network of massive laser observatories. 323 00:15:20.120 --> 00:15:21.879 The pinnacle of precision measurement. 324 00:15:22.159 --> 00:15:26.360 We're talking lasers bouncing down tunnels that are kilometers long, right. 325 00:15:26.840 --> 00:15:29.720 They are capable of detecting changes in distance on the 326 00:15:29.840 --> 00:15:32.799 order of ten to the minus twenty one meters. 327 00:15:32.600 --> 00:15:35.120 Which is what is that? A fraction of a proton? 328 00:15:35.279 --> 00:15:36.919 A tiny fraction of a proton. 329 00:15:37.120 --> 00:15:38.600 It's just absurd, it is. 330 00:15:39.279 --> 00:15:42.799 Over their first three observing runs, the LVK network detected 331 00:15:42.840 --> 00:15:46.759 nearly one hundred confirmed gravitational wave events. 332 00:15:46.279 --> 00:15:49.039 Nearly one hundred black hole and neutron star collisions. 333 00:15:49.159 --> 00:15:52.360 Yes, but the MIT team didn't just use all of them. 334 00:15:52.559 --> 00:15:55.759 They rigorously filtered the data set. They only selected the 335 00:15:55.799 --> 00:15:59.200 twenty eight clearest, most pristine signals. 336 00:15:58.919 --> 00:16:01.559 The gold standard cans. Why only twenty eight? Why not 337 00:16:01.679 --> 00:16:02.679 use all the data? 338 00:16:02.799 --> 00:16:06.000 Because the phase shift we're looking for, this tiny acceleration 339 00:16:06.080 --> 00:16:08.360 in the chirp caused by the dark matter drag, It 340 00:16:08.440 --> 00:16:10.840 is very subtle. Right, If you have a signal that's 341 00:16:10.879 --> 00:16:13.919 buried in instrumental noise, or you know, thermal fluctuations in 342 00:16:13.960 --> 00:16:18.759 the mirrors, or even a tiny seismic vibration that noise 343 00:16:18.759 --> 00:16:20.720 could easily masquerade as a face shift. 344 00:16:20.960 --> 00:16:23.679 H Okay, you'd get a false positive exactly. 345 00:16:24.080 --> 00:16:27.279 By limiting the analysis to the twenty eight highest signal 346 00:16:27.320 --> 00:16:30.639 to noise ratio events, they ensured that any anomaly they 347 00:16:30.759 --> 00:16:34.360 found was likely astrophysical, not just a bumpy laser. 348 00:16:34.519 --> 00:16:37.799 So how did they actually compare their new dictionary to 349 00:16:37.960 --> 00:16:39.399 these twenty eight signals. 350 00:16:39.639 --> 00:16:44.080 They used a technique called matched filtering. Matched filtering, right, 351 00:16:44.080 --> 00:16:47.440 it's standard in this field. You take the incoming noisy 352 00:16:47.519 --> 00:16:50.600 data from the detector and you cross correlate it with 353 00:16:50.679 --> 00:16:52.519 your bank of theoretical templates. 354 00:16:52.559 --> 00:16:54.399 You just slide the template over the data until it 355 00:16:54.440 --> 00:16:54.919 lines up. 356 00:16:55.120 --> 00:16:58.320 Essentially, Yes, if a template matches the signal hidden in 357 00:16:58.360 --> 00:17:00.559 the noise, the cross correlations. 358 00:17:00.080 --> 00:17:01.559 Spikes and you have a match. 359 00:17:01.759 --> 00:17:04.319 Right. So they took these twenty eight pristine in this 360 00:17:04.519 --> 00:17:08.799 and analyzed them twice, once using the standard vacuum template 361 00:17:09.440 --> 00:17:12.720 and once using their brand new dark matter templates. 362 00:17:12.319 --> 00:17:14.680 And they used Bayesian inference to see which one fits 363 00:17:14.720 --> 00:17:17.279 better exact. Okay, this suspense is killing me. What did 364 00:17:17.319 --> 00:17:19.079 they find when they ran the twenty eight candidates? 365 00:17:19.240 --> 00:17:21.559 Well, for twenty seven of the twenty eight candidates. The 366 00:17:21.599 --> 00:17:23.960 Beaesian evidence heavily favored the vacuum model. 367 00:17:24.240 --> 00:17:27.000 Okay, so twenty seven of them were just regular black 368 00:17:27.039 --> 00:17:30.039 holes merging in empty space, or at least the dark 369 00:17:30.079 --> 00:17:32.079 matter was too thin to notice. 370 00:17:31.759 --> 00:17:34.000 Right, But one event broke the pattern. 371 00:17:34.039 --> 00:17:37.160 Here we go GW one nine zero seven to two eight. 372 00:17:37.160 --> 00:17:41.400 Yes, detected on July twenty eighth, twenty nineteen. It was 373 00:17:41.440 --> 00:17:44.160 a merger of two black holes with a combined mass 374 00:17:44.240 --> 00:17:46.079 roughly twenty times that of our son. 375 00:17:46.240 --> 00:17:48.759 Okay, a twenty solar mass collision, and. 376 00:17:48.680 --> 00:17:52.559 The Beaesian analysis of this specific signal showed a preference 377 00:17:52.720 --> 00:17:55.400 for the dark matter model over the vacuum model. 378 00:17:55.160 --> 00:17:58.200 A preference meaning it fit the dark matter dictionary better 379 00:17:58.240 --> 00:17:59.960 than the empty space dictionary exactly. 380 00:18:00.279 --> 00:18:04.400 It exhibited that anomalous phase evolution that slight acceleration in 381 00:18:04.440 --> 00:18:07.680 the chirp that perfectly aligns with the dynamical friction of 382 00:18:07.680 --> 00:18:08.640 a bisonic cloud. 383 00:18:08.799 --> 00:18:10.599 Okay, I have to stop you there because I am 384 00:18:10.640 --> 00:18:13.480 getting incredibly excited. But I also need to play Devil's advocate. 385 00:18:13.559 --> 00:18:15.599 Go for it. If they found a signal that literally 386 00:18:15.640 --> 00:18:19.240 matches the dark matter model, why aren't physicists throwing a 387 00:18:19.279 --> 00:18:22.000 global parade right now? Like, why isn't this front page 388 00:18:22.079 --> 00:18:23.960 news everywhere? Why is it just a preference? 389 00:18:24.240 --> 00:18:28.240 This raises an important question about the threshold of scientific discovery, 390 00:18:28.839 --> 00:18:33.720 and the researchers, particularly show su Arikoetsia from MIT, we're 391 00:18:33.839 --> 00:18:34.680 very very. 392 00:18:34.519 --> 00:18:37.440 Cautious about this because in physics you can't just say 393 00:18:37.720 --> 00:18:38.640 looks pretty good to me. 394 00:18:38.880 --> 00:18:42.759 You really can't. In Baesian statistics, you calculate something called 395 00:18:42.799 --> 00:18:45.559 the Bayes factor. It's a ratio that tells you how 396 00:18:45.640 --> 00:18:48.200 much the data shifts your belief from one model to 397 00:18:48.240 --> 00:18:50.920 the other. Okay, so a Bayes factor might say the 398 00:18:51.000 --> 00:18:55.720 data is ten times or one hundred times more probable 399 00:18:56.039 --> 00:18:56.400 under the. 400 00:18:56.440 --> 00:18:58.119 Dark matter model, which sounds great. 401 00:18:58.240 --> 00:19:01.240