WEBVTT 1 00:00:03.439 --> 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 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.920 --> 00:00:29.160 I want you to imagine, just for a second, that 8 00:00:29.320 --> 00:00:32.039 you have this ability to peer all the way back 9 00:00:32.079 --> 00:00:35.799 in time, right to the very edge of the observable universe. 10 00:00:35.520 --> 00:00:38.399 Which is a mind bending concept on its own, honestly, Ollie. 11 00:00:38.520 --> 00:00:41.640 Absolutely, we're talking about looking at a time that's less 12 00:00:41.679 --> 00:00:44.200 than five hundred and fifty million years after the Big 13 00:00:44.240 --> 00:00:49.399 Bang and based on well basically everything after physicists have 14 00:00:49.439 --> 00:00:53.640 mathematically modeled for decades. If you look back that far 15 00:00:54.159 --> 00:00:56.880 to a red shift of roughly ten or twelve, you 16 00:00:56.960 --> 00:00:59.119 have a very specific expectation of what you're. 17 00:00:59.039 --> 00:01:01.399 Going to see, very established baseline. 18 00:01:01.479 --> 00:01:05.640 Yeah, you're expecting to find these dark, faint, heavily obscured, 19 00:01:05.920 --> 00:01:09.319 dusty smudges of nascent galaxies. You're looking for these tiny 20 00:01:09.319 --> 00:01:12.040 structures just barely starting to pull themselves together out of 21 00:01:12.079 --> 00:01:13.120 the primordial gas. 22 00:01:13.200 --> 00:01:16.680 Yeah, the expectation was essentially one of extreme optical dimness, 23 00:01:17.000 --> 00:01:19.840 because you know, you're looking for the absolute earliest structures 24 00:01:19.840 --> 00:01:22.439 in the PASMO, so the assumption is that they are shrouded, 25 00:01:22.560 --> 00:01:27.400 like completely hidden, exactly hidden behind thick, undisturbed veils of 26 00:01:27.400 --> 00:01:30.879 this pristine cosmic material. It was supposed to be this 27 00:01:31.040 --> 00:01:35.040 very quiet, almost murky picture of the early universe where 28 00:01:35.120 --> 00:01:37.760 the light of the first stars is just heavily suffocated 29 00:01:37.799 --> 00:01:39.200 by their surrounding environment. 30 00:01:39.480 --> 00:01:42.560 So, keeping that expectation in mind, put yourself in the 31 00:01:42.599 --> 00:01:45.879 shoes of the astronomical community. When the James Web Space 32 00:01:45.920 --> 00:01:50.000 Telescope finally opened its golden mirrors, calibrated the near infrared 33 00:01:50.040 --> 00:01:53.280 camera and actually looked at that exact epoch. 34 00:01:53.000 --> 00:01:57.560 The collective shock was I mean, it was palpable because 35 00:01:57.560 --> 00:02:02.000 instead of those faint, dusty smudges, JWST found an early universe. 36 00:02:02.040 --> 00:02:04.519 It was absolutely a blaze. It was just filled with 37 00:02:04.560 --> 00:02:10.159 galaxy shining with its unexpectedly intense, brilliant, unfiltered ultraviolet light. 38 00:02:10.360 --> 00:02:13.439 It was a profound contradiction to all the established models 39 00:02:13.439 --> 00:02:16.919 of galactic evolution. And the brightness wasn't just some slight 40 00:02:16.960 --> 00:02:20.520 calibration error or minor anomaly. Right, these objects were orders 41 00:02:20.560 --> 00:02:23.199 of magnitude brighter and the rest fering ultraviolet than the 42 00:02:23.199 --> 00:02:25.639 prevailing theories of galaxy formation could account for. 43 00:02:25.879 --> 00:02:26.840 Orders of magnitude. 44 00:02:26.919 --> 00:02:30.039 Yeah, it completely upended our understanding of what the cosmic 45 00:02:30.120 --> 00:02:31.240 dawn actually looked like. 46 00:02:31.560 --> 00:02:34.039 To put the scale of this shock into perspective for you, 47 00:02:34.680 --> 00:02:37.479 imagine you're an explorer who uncovers a hidden door in 48 00:02:37.520 --> 00:02:40.680 an ancient ruin, and based on all the historical texts, 49 00:02:41.039 --> 00:02:44.479 you expect to open it and find like a dimly lit, 50 00:02:44.560 --> 00:02:47.520 smoky nineteen twenty speakeasy. 51 00:02:47.000 --> 00:02:49.840 Shattery figures heavy atmosphere. 52 00:02:49.319 --> 00:02:52.759 Right, fick cigar smoke blocking the dim incandescent bulbs, maybe 53 00:02:52.800 --> 00:02:55.400 a single piano playing quietly in the corner. But you 54 00:02:55.439 --> 00:02:58.280 swing the door open and you are instantly blasted by 55 00:02:58.319 --> 00:03:00.319 a modern stadium rock concert. 56 00:03:00.039 --> 00:03:01.919 Blinding lasers, pyrotechnics. 57 00:03:02.039 --> 00:03:04.919 Yes, the atmosphere is totally clear of smoke and the 58 00:03:04.919 --> 00:03:07.719 amplifiers are turned up to eleven. That is the level 59 00:03:07.719 --> 00:03:09.960 of absolute whiplash we are dealing with here, and that 60 00:03:10.000 --> 00:03:12.319 brings us to the core mystery we are unpacking today. 61 00:03:12.439 --> 00:03:16.159 We're looking at a high space astrophysical anomaly. How is 62 00:03:16.199 --> 00:03:18.240 the early universe so impossibly bright? 63 00:03:18.560 --> 00:03:21.319 And the most fascinating part is that the central thesis, 64 00:03:21.360 --> 00:03:24.479 the actual physical mechanism that solves this puzzle, it doesn't 65 00:03:24.520 --> 00:03:25.680 lie in the stars themselves. 66 00:03:26.080 --> 00:03:28.639 It doesn't, and that forces us to look away from 67 00:03:28.680 --> 00:03:31.759 the light sources and actually examine the medium the light 68 00:03:31.800 --> 00:03:34.960 travels through. It lies in something that sounds oh, kind 69 00:03:35.000 --> 00:03:38.120 of mundane on the surface, but it operates on deeply 70 00:03:38.159 --> 00:03:41.280 complex physical principles, ancient cosmic dust. 71 00:03:41.439 --> 00:03:41.719 Right. 72 00:03:42.240 --> 00:03:45.400 But to understand why this brightness was such a massive shock, 73 00:03:45.840 --> 00:03:48.159 we first really have to understand the mechanics of why 74 00:03:48.199 --> 00:03:51.319 these early galaxies were supposed to be dim. So let's 75 00:03:51.400 --> 00:03:54.800 unpack the anatomy of a cosmic shroud. Why do our 76 00:03:54.840 --> 00:03:59.479 baseline models dictate that young star forming galaxies should appear 77 00:03:59.560 --> 00:04:00.879 dark to outside observer. 78 00:04:01.159 --> 00:04:03.560 Well, it basically comes down to a fundamental mechanism in 79 00:04:03.560 --> 00:04:06.080 astrophysics known as a tenuation. When we talk about a 80 00:04:06.159 --> 00:04:08.800 young galaxy, we're talking about a region experiencing a violent, 81 00:04:08.919 --> 00:04:13.159 furious rate of star formation. These localized areas are giant 82 00:04:13.159 --> 00:04:16.519 molecular clodes, often called stellar nurseries. 83 00:04:16.639 --> 00:04:18.199 Okay, so stellar nursery yeah. 84 00:04:18.480 --> 00:04:21.839 Now, when a new star ignites, especially the massive really 85 00:04:21.879 --> 00:04:24.319 hot O type and B type stars that dominate the 86 00:04:24.360 --> 00:04:27.079 light profile of these young galaxies, they pump out an 87 00:04:27.160 --> 00:04:29.959 enormous flux of high energy ultraviolet radiation. 88 00:04:29.959 --> 00:04:34.279 So the stars themselves are undeniably bright. The photon production 89 00:04:34.480 --> 00:04:35.519 is definitely happening. 90 00:04:35.600 --> 00:04:38.399 Oh, the braw photon production is immense. But in the 91 00:04:38.439 --> 00:04:42.680 standard local universe model of a young galaxy, those stellar 92 00:04:42.759 --> 00:04:45.920 nurseries are just completely choked with cosmic dust. 93 00:04:45.839 --> 00:04:47.800 Like the speakeasy smoke exactly. 94 00:04:48.120 --> 00:04:50.600 This dust is mixed right into the gas clouds where 95 00:04:50.639 --> 00:04:53.480 the stars are born, and this dust acts like a 96 00:04:53.560 --> 00:04:57.720 highly efficient optical blanket. So as the ultraviolet photons try 97 00:04:57.720 --> 00:05:00.680 to travel outward from the stellar photosphere escape into the 98 00:05:00.680 --> 00:05:04.319 wider universe, they collide with these microscopic. 99 00:05:03.720 --> 00:05:05.680 Dust grains, and what happened to the light. 100 00:05:05.720 --> 00:05:09.639 Then the dust absorbs the high energy ultraviolet radiation, heats up, 101 00:05:09.800 --> 00:05:13.000 and then re emits that energy as lower energy, longer 102 00:05:13.000 --> 00:05:17.360 wavelength infrared light. Furthermore, the dust physically scatters the remaining 103 00:05:17.480 --> 00:05:20.279 UV light in random directions, deflecting it away from our 104 00:05:20.319 --> 00:05:24.199 line of sight. So this combined process of absorption and scattering, 105 00:05:24.319 --> 00:05:25.279 that is attenuation. 106 00:05:25.560 --> 00:05:28.800 So from the perspective of an outside observer like JAWST 107 00:05:29.000 --> 00:05:33.079 sitting out at lagrange point two, that galaxy appears incredibly 108 00:05:33.120 --> 00:05:36.720 dim in the ultraviolet spectrum because the internal dust blanket 109 00:05:36.720 --> 00:05:40.480 has essentially swallowed or deflected all that high energy light 110 00:05:40.720 --> 00:05:43.759 before it could escape the galaxy's gravitational. 111 00:05:43.079 --> 00:05:47.600 Well precisely, the standard local model operates on a proportional assumption. 112 00:05:48.399 --> 00:05:51.519 Lots of massive young stars means lots of heavy elements 113 00:05:51.560 --> 00:05:55.680 being processed, which equals a thick, efficient dust blanket, which 114 00:05:55.680 --> 00:05:58.000 equals a severely dimmed Redder galaxy. 115 00:05:58.279 --> 00:06:02.639 But JWST looks out, detects the distinct signatures of massive 116 00:06:02.680 --> 00:06:06.439 young star populations, but sees them blazing bright in the UV. 117 00:06:06.759 --> 00:06:10.560 Yeah, the blanket is fundamentally failing to attenuate the light. 118 00:06:10.680 --> 00:06:13.120 The blanket is missing or the physics of the blanket 119 00:06:13.120 --> 00:06:16.720 are broken. That was the immediate crisis in cosmology, and 120 00:06:16.759 --> 00:06:20.399 whenever there's a sudden glaring contradiction between observation and theory, 121 00:06:20.680 --> 00:06:23.480 the community scrambles to line up alternative suspects, right. 122 00:06:23.399 --> 00:06:25.800 Because you need to explain this missing attenuation, and you 123 00:06:25.879 --> 00:06:27.600 need to do it without breaking the laws. 124 00:06:27.360 --> 00:06:30.720 Of physics exactly. So let's dig into the initial lineup 125 00:06:30.720 --> 00:06:33.639 of suspects, because we really have to understand why the 126 00:06:33.720 --> 00:06:36.839 obvious answers were mathematically wrong before we get to the 127 00:06:36.839 --> 00:06:37.399 real answer. 128 00:06:37.560 --> 00:06:40.199 The initial reaction is always to look for a loophole 129 00:06:40.279 --> 00:06:42.680 in the existing frameworks before you go inventing new ones. 130 00:06:42.759 --> 00:06:46.240 Right, So, suspect number one was the idea that maybe 131 00:06:46.279 --> 00:06:50.040 the dust is there behaving normally, but these galaxies are 132 00:06:50.079 --> 00:06:55.720 just experiencing insanely violent, sustained bursts of star formation the 133 00:06:55.759 --> 00:06:58.720 superstar burst theory, like the idea that they are just 134 00:06:58.920 --> 00:07:00.199 overwhelmingly bright. 135 00:07:00.399 --> 00:07:04.079 Yes, the hypothesis was that the sheer volume of ultraviolet 136 00:07:04.120 --> 00:07:08.959 photon production was so astronomically high that it simply saturated 137 00:07:08.959 --> 00:07:12.879 the dust's capacity to absorb it, just overpowering the blanket. 138 00:07:12.480 --> 00:07:13.319 Pushing right through it. 139 00:07:13.399 --> 00:07:16.319 Exactly. But that theory falls apart the moment you apply 140 00:07:16.439 --> 00:07:19.279 rigorous fluid dynamics and look at the Eddington limit. 141 00:07:19.399 --> 00:07:22.120 Okay, let's define the Eddington limit for the listener, because 142 00:07:22.160 --> 00:07:25.040 that's the absolute hard ceiling for this theory, right it is. 143 00:07:25.040 --> 00:07:28.199 The Eddington limit is basically the natural balance point between 144 00:07:28.240 --> 00:07:32.399 gravity pulling matter inward and radiation pressure pushing it outward. 145 00:07:32.279 --> 00:07:34.600 Radiation pressure, so light pushing on things. 146 00:07:34.680 --> 00:07:38.639 Yes, photons carry momentum. If you pack too many massive 147 00:07:38.800 --> 00:07:42.680 ultra bright stars into a confined giant molecular cloud, the 148 00:07:42.720 --> 00:07:46.160 physical outward pressure of their combined light becomes stronger than 149 00:07:46.199 --> 00:07:49.040 the gravitational binding energy of the gas cloud itself. 150 00:07:49.079 --> 00:07:52.399 The light is literally so intense it acts as a 151 00:07:52.439 --> 00:07:55.279 physical force that pushes the gas away exactly. 152 00:07:55.160 --> 00:07:57.920 And if the star formation rate is as absurdly high 153 00:07:57.959 --> 00:08:01.800 as the superstarbust theory requires to overpower the dust, that 154 00:08:01.920 --> 00:08:05.680 intense radiation pressure would physically blow the stellar nursery apart 155 00:08:05.680 --> 00:08:08.720 from the inside out. Wow, the galaxy would unbind its 156 00:08:08.720 --> 00:08:11.680 own star forming gas, and that would immediately shut down 157 00:08:11.680 --> 00:08:16.399 any further star formation. So mathematically, a sustained superstarburst of 158 00:08:16.439 --> 00:08:19.879 that magnitude is self terminating. It's just physically impossible for 159 00:08:19.920 --> 00:08:22.319 them to be that bright for the durations we're actually observing. 160 00:08:22.480 --> 00:08:24.879 Okay, So superstarbursts or crossed off the list. The math 161 00:08:25.000 --> 00:08:27.439 just doesn't allow it. Suspect number two is a bit 162 00:08:27.480 --> 00:08:30.759 more nuanced. It was the idea of a skewed stellar population, 163 00:08:30.839 --> 00:08:34.440 specifically a wildly different initial mass function or. 164 00:08:34.440 --> 00:08:38.080 IMF right the initial mass function. This is the empirical 165 00:08:38.159 --> 00:08:41.799 rule that dictates the ratio of heavy massive stars to 166 00:08:41.960 --> 00:08:45.120 small low mass stars when a gas cloud. 167 00:08:44.799 --> 00:08:47.279 Collapses, because they don't all form the same size. 168 00:08:47.360 --> 00:08:49.759 No, not at all. In our milky Way. For every 169 00:08:49.840 --> 00:08:54.320 massive brilliant blue star born, you get hundreds of tiny, 170 00:08:54.519 --> 00:08:57.679 dim red dwarfs. It's a very bottom heavy distribution. 171 00:08:58.399 --> 00:09:00.679 But the theory here is that maybe the early universe 172 00:09:00.759 --> 00:09:05.000 was top heavy. Maybe it almost exclusively formed massive ultra. 173 00:09:04.759 --> 00:09:08.600 Bright stars, And the logic makes sense. Initially, a pristine, 174 00:09:08.879 --> 00:09:12.559 metal poor gas cloud in the early universe cools less efficiently, 175 00:09:12.799 --> 00:09:17.200 which leads to larger fragmentation masses, meaning bigger stars. A 176 00:09:17.360 --> 00:09:20.759 top heavy IMF would certainly produce more ultra violet light 177 00:09:20.879 --> 00:09:22.200 per unit of gas masks. 178 00:09:22.279 --> 00:09:23.759 Well, there's a catch, a big catch. 179 00:09:24.000 --> 00:09:26.240 While it helps close the gap slightly, it still couldn't 180 00:09:26.240 --> 00:09:29.639 account for the systemic universe wide lack of attenuation Jaabst 181 00:09:29.879 --> 00:09:33.799 was seeing. Furthermore, massive stars die quickly, and they eject 182 00:09:33.840 --> 00:09:36.720 massive amounts of dust forming heavy elements. When they do so, 183 00:09:36.759 --> 00:09:39.399 they would make a ton of dust really fast exactly. 184 00:09:39.440 --> 00:09:42.600 A top heavy IMF would rapidly pollute the galaxy, creating 185 00:09:42.600 --> 00:09:46.879 an even thicker dust blanket very quickly, which completely contradicts 186 00:09:46.879 --> 00:09:49.200 the sustained bright UV observations. 187 00:09:49.480 --> 00:09:52.759 So a top heavy stellar population ultimately chokes itself out 188 00:09:52.759 --> 00:09:56.000 with its own dust. Okay. Suspect number three was to 189 00:09:56.120 --> 00:10:00.919 look away from stars entirely hidden black holes active galactic 190 00:10:01.000 --> 00:10:02.559 nuclei or AGNs. 191 00:10:02.720 --> 00:10:06.919 AGNs are incredibly efficient engines. When a super vassive black 192 00:10:06.919 --> 00:10:10.440 hole at the center of a galaxy actively accrete surrounding gas, 193 00:10:10.519 --> 00:10:14.080 that gas forms a wildly energetic accretion disk. 194 00:10:14.080 --> 00:10:16.399 Just swirling around the event horizon. 195 00:10:16.080 --> 00:10:19.240 Right The friction and gravitational compression heat that disk to 196 00:10:19.320 --> 00:10:22.919 millions of degrees, causing it to shine brilliantly in the ultraviolet, 197 00:10:23.200 --> 00:10:25.840 and it can often outshine the entire host galaxy. 198 00:10:26.039 --> 00:10:28.399 So the thought was, maybe we aren't looking at starlight 199 00:10:28.440 --> 00:10:30.960 at all. Maybe every single one of these early bright 200 00:10:31.000 --> 00:10:33.639 spots is just a feeding black hole masking itself as 201 00:10:33.679 --> 00:10:34.200 a galaxy. 202 00:10:34.240 --> 00:10:37.000 It's a very compelling idea. But we don't just look 203 00:10:37.039 --> 00:10:39.559 at pictures. We take spectra. We take the incoming light 204 00:10:39.600 --> 00:10:42.879 and split it into its component wavelengths like a prism exactly, 205 00:10:43.360 --> 00:10:47.720 and an agan accretion disc produces a very distinct chemical fingerprint, 206 00:10:48.240 --> 00:10:53.120 specifically extremely broad emission lines from high velocity gas swirling 207 00:10:53.159 --> 00:10:56.960 near the event horizon and highly ionized elements that require 208 00:10:57.000 --> 00:11:00.720 extreme radiation fields to exist, like I and eil helium 209 00:11:00.840 --> 00:11:01.679 or carbon five. 210 00:11:01.799 --> 00:11:06.200 And when JWST's near infrared spectrograph actually look for those 211 00:11:06.240 --> 00:11:08.159 specific fingerprints. 212 00:11:07.559 --> 00:11:10.159 They largely weren't there. Not in the general population of 213 00:11:10.200 --> 00:11:13.399 these bright galaxies. The spectra didn't match the violent, high 214 00:11:13.519 --> 00:11:17.480 energy physics of an accretion disk. They clearly displayed the narrower, 215 00:11:17.720 --> 00:11:21.200 lower ionization signatures of stellar photospheres, so. 216 00:11:21.159 --> 00:11:23.039 The light was undeniably coming from star. 217 00:11:23.200 --> 00:11:24.840 It was definitely starlight. 218 00:11:24.639 --> 00:11:27.480 Which brings us to the final and most fiercely debated 219 00:11:27.759 --> 00:11:31.279 discarded theory, the leaf blower theory, technically known as violent 220 00:11:31.320 --> 00:11:35.480 stellar feedback or momentum driven galactic winds. I want to 221 00:11:35.480 --> 00:11:37.320 spend some time on this because it really dominated the 222 00:11:37.360 --> 00:11:40.039 discourse and its failure is what leads us to the 223 00:11:40.080 --> 00:11:40.879 actual answer. 224 00:11:41.320 --> 00:11:45.120 Yeah, it's a very intuitive model. Honestly. The stellar feedback 225 00:11:45.159 --> 00:11:48.919 theory hinges on the fact that massive young stars are chaotic, 226 00:11:49.120 --> 00:11:54.399 violent neighbors. They emit ferocious stellar windstreams of charged particles 227 00:11:54.480 --> 00:11:58.679 flying off their surfaces, and crucially they end their short 228 00:11:58.679 --> 00:12:01.879 lives in supernovac's. 229 00:12:00.600 --> 00:12:02.559 And the theory proposes that if you pack enough of 230 00:12:02.600 --> 00:12:05.919 these massive stars into a young galaxy, there combined cellar 231 00:12:05.960 --> 00:12:10.480 winds and overlapping supernova shockwaves merge together to create a 232 00:12:10.519 --> 00:12:14.639 macro scale event like a literal galactic scale hurricane sweeping 233 00:12:14.679 --> 00:12:15.360 outward from the. 234 00:12:15.360 --> 00:12:19.279 Galactic core, exactly a mechanical clearing of the interstellar medium. 235 00:12:19.720 --> 00:12:23.320 The hypothesis was that this combined kinetic energy simply blasted 236 00:12:23.320 --> 00:12:27.120 the dust entirely out of the galaxy's gravitational. 237 00:12:26.440 --> 00:12:28.279 Well, just blowing the smoke right out of the. 238 00:12:28.279 --> 00:12:30.840 Room, ejecting it into the intergalactic medium and leaving the 239 00:12:30.840 --> 00:12:34.799 stellar populations completely exposed, resulting in the blazing UV light 240 00:12:34.919 --> 00:12:35.399 we see. 241 00:12:35.679 --> 00:12:38.720 I totally get the appeal of the idea the stars 242 00:12:38.720 --> 00:12:40.960 build the blanket and then the stars immediately blow the 243 00:12:40.960 --> 00:12:44.399 blanket away, But I really have to push back on 244 00:12:44.480 --> 00:12:47.559 the fluid dynamics of this, because I think the whole 245 00:12:48.000 --> 00:12:52.799 leaf blower analogy reveals a massive logical flaw when you 246 00:12:52.840 --> 00:12:56.039 apply it to a multi phase interstellar medium. Oh absolutely, 247 00:12:56.879 --> 00:12:59.360 Like if you have a sandbox, right, and it's full 248 00:12:59.399 --> 00:13:03.159 of heavy sand, which represents the dense, cold molecular gas 249 00:13:03.200 --> 00:13:05.639 where stars form, and there's a layer of fine like 250 00:13:05.759 --> 00:13:08.559 dust mixed all into it. If you take an industrial 251 00:13:08.759 --> 00:13:11.399 high powered leaf blower and point it at the sandbox 252 00:13:11.440 --> 00:13:14.200 to clear away the dust, you aren't just selectively removing 253 00:13:14.200 --> 00:13:14.559 the dust. 254 00:13:14.679 --> 00:13:17.120 No, you're not, because they are dynamically coupled. 255 00:13:17.279 --> 00:13:20.480 Right. The kinetic force required to eject all those microscopic 256 00:13:20.559 --> 00:13:23.600 dust particles against the gravitational pull of an entire galaxy 257 00:13:23.840 --> 00:13:27.559 would absolutely obliterate the cold hydrogen gas clouds as well. 258 00:13:27.720 --> 00:13:30.919 You would blow away all the sand, and galaxies explicitly 259 00:13:31.000 --> 00:13:34.240 need that cold, dense molecular gas to continue forming stars. 260 00:13:34.960 --> 00:13:37.279 If a galactic wind is powerful enough to clear out 261 00:13:37.279 --> 00:13:39.679 the dust blanket entirely, wouldn't it also clear out the 262 00:13:39.679 --> 00:13:42.639 star forming fuel, effectively killing the galaxy. 263 00:13:42.960 --> 00:13:47.159 That is precisely the hydrodynamical contradiction that dismantled the stellar 264 00:13:47.200 --> 00:13:50.799 feedback theory. Dust and gas are not separate entities floating 265 00:13:50.840 --> 00:13:53.679 side by side. They are intimately mixed. The dust is 266 00:13:53.759 --> 00:13:55.080 kinetically coupled to the. 267 00:13:55.039 --> 00:13:56.440 Gas, so they move together. 268 00:13:56.720 --> 00:14:00.559 Exactly if a shockwave sweeps the dust away, sweeps the 269 00:14:00.600 --> 00:14:03.320 gas away, and the question you just asked, how could 270 00:14:03.360 --> 00:14:06.279 a galaxy blow away its dust without blowing away its 271 00:14:06.279 --> 00:14:09.279 fuel is what astronomers specifically set out. 272 00:14:09.159 --> 00:14:12.360 To test, and to test it, they couldn't just use JWST. 273 00:14:12.919 --> 00:14:15.559 They needed to look for the cold gas, the sand 274 00:14:16.000 --> 00:14:18.120 in the sandbox, and this is where we find the 275 00:14:18.120 --> 00:14:22.240 smoking gun. Astronomers pair JWST's data with observations from a 276 00:14:22.279 --> 00:14:25.879 completely different type of observatory here on Earth, the Atacama 277 00:14:26.039 --> 00:14:29.320 Large Millimeter Submillimeter Array or LMA. 278 00:14:29.639 --> 00:14:31.919 LMA is an incredible facility, and. 279 00:14:31.879 --> 00:14:35.159 By combining these two wildly different views, they isolated a 280 00:14:35.200 --> 00:14:39.240 specific classification of galaxies that broke the leaf blower theory permanently. 281 00:14:39.480 --> 00:14:41.039 They identified jeldice. 282 00:14:40.759 --> 00:14:44.080 Jeldice galaxies with extremely low dust attenuation. 283 00:14:44.519 --> 00:14:47.840 Let's break down exactly how these two observatories operate together, 284 00:14:47.879 --> 00:14:52.759 because it's critical to understanding the paradox they uncovered. JWST 285 00:14:52.879 --> 00:14:56.840 is operating in space looking near infrared light. LMA is 286 00:14:56.879 --> 00:15:00.159 down in the Chilean desert looking at millimeter wavelengths. How 287 00:15:00.200 --> 00:15:03.200 do they work together to look at the exact same object. 288 00:15:03.440 --> 00:15:07.440 It's all about complementary spectroscopy. So JWST is designed to 289 00:15:07.480 --> 00:15:11.000 capture the light emitted directly by stars, but because these 290 00:15:11.039 --> 00:15:13.799 galaxies are so far away, say a redshift of ten, 291 00:15:14.240 --> 00:15:17.480 the expansion of the universe has stretched their original ultraviolet 292 00:15:17.559 --> 00:15:20.279 light all the way down into the infrared spectrum. By 293 00:15:20.279 --> 00:15:21.399 the time it reaches. 294 00:15:21.120 --> 00:15:25.000 Us, the light gets physically stretched over thirteen billion years right. 295 00:15:24.919 --> 00:15:28.919 And JWST captures that red shifted starlight and confirms definitively 296 00:15:29.200 --> 00:15:33.799 that the ultraviolet light is escaping these geldas unimpeded. To JWST, 297 00:15:33.879 --> 00:15:35.840 the dust blanket is functionally non existent. 298 00:15:36.000 --> 00:15:38.559 It sees the blazing stars, but alli may isn't looking 299 00:15:38.559 --> 00:15:39.519 for stars at all now. 300 00:15:39.759 --> 00:15:42.960 Al May is an interferometer specifically tuned to detect the 301 00:15:42.960 --> 00:15:46.399 thermal continuum of cold dust and more importantly, the specific 302 00:15:46.559 --> 00:15:50.759 rotational transition lines of molecules in cold gas. Specifically, it 303 00:15:50.799 --> 00:15:52.559 looks for carbon monoxide or CO. 304 00:15:53.159 --> 00:15:56.759 Wait, why carbon monoxide if the galaxy is mostly hydrogen. 305 00:15:56.879 --> 00:16:01.240 It's a great question because cold molecular hydrogen twenty two 306 00:16:01.240 --> 00:16:04.200 to two dollars is a symmetric molecule, and it lacks 307 00:16:04.200 --> 00:16:07.399 a dipole moment, meaning it's practically invisible at the frigid 308 00:16:07.399 --> 00:16:10.879 temperatures of deep space, it just doesn't emit radiation easily. 309 00:16:11.519 --> 00:16:15.919 But carbon monoxide is highly asymmetric. As CO molecules tumble 310 00:16:15.960 --> 00:16:18.559 and rotate in these cold gas clouds, they drop down 311 00:16:18.600 --> 00:16:22.600 quantum energy levels and emit very specific bright photons at 312 00:16:22.600 --> 00:16:27.600 millimeter wavelengths. ALMA detects these CO emissions and uses them 313 00:16:27.639 --> 00:16:31.159 as a direct, reliable mathematical tracer to calculate the total 314 00:16:31.240 --> 00:16:34.799 mass of the invisible cold hydrogen gas hiding in the galaxy. 315 00:16:34.879 --> 00:16:38.799 Okay, so GWST measures the starlight escaping and LMA measures 316 00:16:38.840 --> 00:16:41.879 the exact volume of the cold star forming gas less 317 00:16:41.879 --> 00:16:42.879 than the tank exactly. 318 00:16:43.120 --> 00:16:46.320 And when a stronomer's pointed LMA at these exact same geldas, 319 00:16:46.360 --> 00:16:50.039 the ones that Jawst insisted had zero dust attenuation, they 320 00:16:50.039 --> 00:16:51.600 found an impossible contradiction. 321 00:16:51.840 --> 00:16:54.679 Sandbox was still completely full of sand full As. 322 00:16:54.559 --> 00:16:58.320 An understatement, the measurements were staggering. These geldas, which are 323 00:16:58.360 --> 00:17:02.840 totally transparent to ultraviolet light, possess massive, undisturbed reservoirs of 324 00:17:02.879 --> 00:17:03.559 cold gas. 325 00:17:03.799 --> 00:17:06.079 What kind of volume are we talking about here? Like? 326 00:17:06.240 --> 00:17:07.480 How gas rich are they? 327 00:17:07.759 --> 00:17:11.680 The metric they use is the gas mass fraction basically 328 00:17:11.920 --> 00:17:14.720 the ratio of the mass of the unformed gas to 329 00:17:15.000 --> 00:17:18.000 the total buryonic mass of the galaxy. In some of 330 00:17:18.000 --> 00:17:21.720 these gel days, the gas fractions exceed ninety percent. 331 00:17:21.960 --> 00:17:24.440 Wait, let me make sure I'm understanding that ninety percent 332 00:17:24.480 --> 00:17:26.960 of the entire normal matter mass of the galaxy is 333 00:17:27.000 --> 00:17:31.079 just raw unformed gas. Only ten percent has actually condensed 334 00:17:31.079 --> 00:17:31.680 into stars. 335 00:17:31.839 --> 00:17:35.880 Yes, they are incredibly inefficient at forming stars at this stage. 336 00:17:36.000 --> 00:17:39.400 They are essentially these vast swirling oceans of raw fuel 337 00:17:39.720 --> 00:17:41.079 barely tacked into. 338 00:17:40.960 --> 00:17:44.240 Okay, if we synthesize these two distinct data points, the 339 00:17:44.359 --> 00:17:47.759 logic is inescapable. The leaf blower theory says the violent 340 00:17:47.799 --> 00:17:50.640 stellar winds blew the dust away, leaving the galaxy bright. 341 00:17:51.160 --> 00:17:53.799 But basic fluidynamic says if a wind was powerful enough 342 00:17:53.839 --> 00:17:56.400 to blast the dust into intercalactic space, it would have 343 00:17:56.480 --> 00:18:00.240 violently evacuated that cold gas reservoir too. Yes, to have 344 00:18:00.240 --> 00:18:02.880 a macroscopic hurricane strong enough to clear all the dust, 345 00:18:03.359 --> 00:18:06.359 but delicate enough to leave a ninety percent gas reservoir 346 00:18:06.359 --> 00:18:08.799 perfectly intact and undisturbed. 347 00:18:08.400 --> 00:18:12.559 It is physically impossible. You cannot decouple the dust from 348 00:18:12.599 --> 00:18:15.920 the gas in a kinetic blowout. Of that magnitude. If 349 00:18:15.960 --> 00:18:19.599 the gas is still there, resting quietly in massive quantities, 350 00:18:19.839 --> 00:18:21.599 then the mechanical blowout. 351 00:18:21.240 --> 00:18:26.200 Never happen, which leaves only one terrifyingly weird conclusion. Because 352 00:18:26.200 --> 00:18:32.119 the massive gas reservoir is definitively still sitting there, the 353 00:18:32.240 --> 00:18:34.519 dust must still be there too. The blanket hasn't been 354 00:18:34.519 --> 00:18:38.200 blown away. The dust is still physically present inside the galaxy. 355 00:18:38.559 --> 00:18:40.920 The dust is absolutely there. It is mixed into the 356 00:18:40.960 --> 00:18:44.720 gas just as we expect, but it is fundamentally failing 357 00:18:44.720 --> 00:18:47.519 to act like normal dust. It has somehow become for 358 00:18:47.559 --> 00:18:51.039 all intents and purposes, optically invisible to the ultraviolet light 359 00:18:51.079 --> 00:18:52.000 produced by the stars. 360 00:18:52.039 --> 00:18:52.880 Invisible dust. 361 00:18:53.000 --> 00:18:56.240 Yeah, it is no longer absorbing or scattering the short wavelengths. 362 00:18:56.240 --> 00:18:59.240 It is just letting them pass right through an invisible blanket. Yeah. 363 00:18:59.279 --> 00:19:01.920 Okay, this is what the mystery pivots entirely. We move 364 00:19:01.960 --> 00:19:04.839 from where did the dust go? To what the hell 365 00:19:04.880 --> 00:19:07.720 is wrong with the microscopic physics of this early universe dust? Exactly, 366 00:19:07.720 --> 00:19:11.240 because if the dust is definitively present but behaving invisibly, 367 00:19:11.839 --> 00:19:13.960 we have to look at how it was manufactured. We 368 00:19:14.000 --> 00:19:16.640 have to compare the dust floating around our modern milky 369 00:19:16.680 --> 00:19:19.640 Way with the dust that existed five hundred million years 370 00:19:19.640 --> 00:19:22.759 after the Big Bang. We have to examine the cosmic 371 00:19:22.799 --> 00:19:24.839 factories that build dust grains. 372 00:19:25.200 --> 00:19:28.240 This is a vital distinction, and it's something often glossed over. 373 00:19:28.759 --> 00:19:32.200 Dust is not a fundamental particle like a proton or 374 00:19:32.279 --> 00:19:37.480 an electron. Dust is a complex macroscopic solid structure. It 375 00:19:37.559 --> 00:19:43.000 is a lattice of heavy elements, silicates, graphites, polycyclic aromatic hydrocarbons. 376 00:19:43.039 --> 00:19:44.079 It has to be assembled right. 377 00:19:44.200 --> 00:19:47.440 It has to be chemically manufactured, and the dominant manufacturing 378 00:19:47.480 --> 00:19:50.240 process in the universe today is fundamentally different from the 379 00:19:50.279 --> 00:19:53.119 only process available thirteen billion years ago. 380 00:19:53.440 --> 00:19:56.279 Let's ground this in the present day. First, how does 381 00:19:56.400 --> 00:19:59.799 mature light blocking dust form in a modern galaxy like ours? 382 00:20:00.160 --> 00:20:03.079 In a mature galaxy, the vast majority of interstellar dust 383 00:20:03.160 --> 00:20:06.640 is created through a slow, incredibly gradual process known as 384 00:20:06.720 --> 00:20:10.039 interstellar grain growth or gas phase accretion. It happens deep 385 00:20:10.079 --> 00:20:12.279 inside the cold, dense molecular clouds. 386 00:20:12.319 --> 00:20:13.039 How does it start. 387 00:20:13.240 --> 00:20:16.759 The process starts with a tiny seed particle, usually a 388 00:20:16.759 --> 00:20:20.200 microscopic silicate core, that was gently puffed out into space 389 00:20:20.599 --> 00:20:23.960 by the stellar wind of an aging relatively low mass 390 00:20:23.960 --> 00:20:27.680 star like an asymptotic giant branch or AGB star. 391 00:20:27.880 --> 00:20:30.759 A tiny little speck of soot floating in the void. 392 00:20:30.759 --> 00:20:33.759 A very small spec and as that speck drifts through 393 00:20:33.759 --> 00:20:38.079 the cold interstellar gas, it very slowly encounters heavier elements. 394 00:20:38.200 --> 00:20:40.960 Astronomers call the metals that are free floating in the 395 00:20:40.960 --> 00:20:45.759 gas phase atoms of iron, carbon, silicon, oxygen. When an 396 00:20:45.799 --> 00:20:49.319 atom physically bumps into the seed, it sticks, it chemically 397 00:20:49.319 --> 00:20:50.359 bonds to the surface. 398 00:20:50.440 --> 00:20:53.079 It's an accretion process layer by layer exactly. 399 00:20:53.240 --> 00:20:55.680 But you have to remember that even a dense molecular 400 00:20:55.680 --> 00:20:58.079 cloud in space is essentially a harder vacuum than anything 401 00:20:58.119 --> 00:21:00.839