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 --> 00:00:26.920 slumber under the night sky. 7 00:00:26.960 --> 00:00:29.760 If you look up at the Milky Way tonight, you know, 8 00:00:29.879 --> 00:00:32.640 you might think you're looking at a peaceful, eternal home. 9 00:00:32.920 --> 00:00:34.840 Oh, absolutely right, like just a. 10 00:00:34.880 --> 00:00:38.399 Quiet neighborhood of stars that has well always been there, 11 00:00:38.520 --> 00:00:40.280 totally untouched and unchanging. 12 00:00:40.479 --> 00:00:41.960 Yeah, that is the common assumption. 13 00:00:42.159 --> 00:00:46.079 But you aren't. You are looking at, honestly, a cosmic 14 00:00:46.159 --> 00:00:50.079 crime scene. It is built entirely from the shredded corpses 15 00:00:50.079 --> 00:00:50.960 of other galaxies. 16 00:00:51.159 --> 00:00:54.399 That is a beautifully grim way to put it, but yeah, 17 00:00:54.399 --> 00:00:55.520 it's totally accurate. 18 00:00:55.640 --> 00:00:59.520 Today our mission is to act as galactic forensic investigators. 19 00:01:00.920 --> 00:01:04.079 We are tracking down the ghost of a lost, ancient 20 00:01:04.200 --> 00:01:06.959 dwarf galaxy that astronomers are calling Loki. 21 00:01:07.519 --> 00:01:10.680 And the most unsettling part is that it isn't millions 22 00:01:10.680 --> 00:01:11.519 of light years away. 23 00:01:11.680 --> 00:01:12.239 No, it's not. 24 00:01:12.640 --> 00:01:16.280 It is hiding right here, like completely embedded within the 25 00:01:16.319 --> 00:01:18.879 structure of our own milky Way, right above our heads. 26 00:01:18.920 --> 00:01:21.640 It's wild. It completely reframes how you look at the. 27 00:01:21.640 --> 00:01:23.959 Night sky, it really does. And I want to establish 28 00:01:24.000 --> 00:01:26.400 the stakes here right at the outset, because trekking down 29 00:01:26.439 --> 00:01:30.079 Loki isn't just about you know, cataloging a few anomalous. 30 00:01:29.519 --> 00:01:31.120 Stars, right, It's bigger than that. 31 00:01:31.120 --> 00:01:35.120 Way bigger. It is about fundamentally rewriting our understanding of 32 00:01:35.159 --> 00:01:37.040 how galaxies actually grow. 33 00:01:37.359 --> 00:01:41.120 So we are literally reading the forensic evidence left behind 34 00:01:41.120 --> 00:01:43.959 by the universe's earliest building blocks exactly. 35 00:01:44.000 --> 00:01:47.200 We're looking at this groundbreaking work by Federico Sostino and 36 00:01:47.200 --> 00:01:50.280 his colleagues. Yeah, and this is really about peering back 37 00:01:50.359 --> 00:01:54.200 to the most violent epochs of the cosmos to understand 38 00:01:54.959 --> 00:01:57.159 the literal architecture of our own existence. 39 00:01:57.200 --> 00:02:01.200 Well, let's start with that architecture, because to even comprehend 40 00:02:01.280 --> 00:02:04.359 where this lost galaxy Loki came from, we have to 41 00:02:04.439 --> 00:02:06.560 kind of shatter the illusion of the Milky. 42 00:02:06.239 --> 00:02:08.479 Way, the majestic spiral illusion, right. 43 00:02:08.439 --> 00:02:10.800 The idea that it just I don't know, popped into existence, 44 00:02:10.919 --> 00:02:14.120 is this solitary, majestic thing. The harsh reality is that 45 00:02:14.319 --> 00:02:17.159 our galaxy is a cannibal. A cannibal add to eat 46 00:02:17.199 --> 00:02:17.560 to grow. 47 00:02:17.919 --> 00:02:22.919 Cannibal is definitely the most accurate, if slightly gruesome, way 48 00:02:22.960 --> 00:02:25.439 to describe it. In extra physics, we call it hierarchical 49 00:02:25.479 --> 00:02:28.479 galaxy formation, right, because the Milky Way did not form 50 00:02:28.520 --> 00:02:31.719 an isolation as this gargante wind structure we see today. 51 00:02:31.759 --> 00:02:33.479 It grew over billions. 52 00:02:33.039 --> 00:02:35.039 Of years by eating smaller guys. 53 00:02:35.159 --> 00:02:40.280 Exactly by consuming smaller galaxies. Astronomers politely refer to this 54 00:02:40.319 --> 00:02:42.039 as merging, but. 55 00:02:42.599 --> 00:02:43.960 I feel like that term is doing a lot of 56 00:02:43.960 --> 00:02:44.560 heavy lifting. 57 00:02:44.719 --> 00:02:48.080 Oh, it wildly misrepresents the physics involved. 58 00:02:47.879 --> 00:02:50.319 Right, because merging makes it sound like, I don't know, 59 00:02:50.400 --> 00:02:53.439 two companies shaking hands into green to share an office. 60 00:02:53.120 --> 00:02:55.599 Building, the very peaceful corporate merger. 61 00:02:55.960 --> 00:02:59.560 Yeah, a neat mutual agreement. But I imagine the mechanics 62 00:02:59.599 --> 00:03:02.199 of these earthactic gatbox where anything but neat. 63 00:03:02.639 --> 00:03:05.439 Far from it. When we look back at the early universe, 64 00:03:05.439 --> 00:03:08.280 we see these smaller systems, these dwarf. 65 00:03:07.919 --> 00:03:09.520 Galaxies, the little guys. 66 00:03:09.560 --> 00:03:12.560 The little guys. Yeah, and they served as the foundational 67 00:03:12.599 --> 00:03:14.120 building blocks of the cosmos. 68 00:03:14.280 --> 00:03:15.360 Okay, So as. 69 00:03:15.199 --> 00:03:19.000 The Protomilky Way began to grow. Its immense gravitational well 70 00:03:19.000 --> 00:03:22.400 would essentially catch these smaller galaxies like a spider web 71 00:03:22.919 --> 00:03:25.560 sort of, but much more violent, because when a dwarf 72 00:03:25.560 --> 00:03:28.159 galaxy falls in, it doesn't just slide neatly into a 73 00:03:28.240 --> 00:03:29.120 designated orbit. 74 00:03:29.199 --> 00:03:29.879 What happens to. 75 00:03:29.840 --> 00:03:32.199 It It encounters something called tidal forces. 76 00:03:32.280 --> 00:03:35.159 Wait, like the tides on Earth, like the Moon pulling 77 00:03:35.199 --> 00:03:35.759 the oceans. 78 00:03:36.039 --> 00:03:40.479 Exactly like that, but on a massive, terrifying galactic scale. 79 00:03:40.639 --> 00:03:43.240 The gravity on the side of the dwarf galaxy closest 80 00:03:43.240 --> 00:03:46.199 to the Milky Way is pulled significantly harder than the 81 00:03:46.240 --> 00:03:47.159 side facing away. 82 00:03:47.319 --> 00:03:49.319 Oh wow, so it's literally being. 83 00:03:49.159 --> 00:03:52.039 Stretched, stretched, until it hits a critical breaking point. 84 00:03:52.120 --> 00:03:53.400 Yes, that sounds intense. 85 00:03:53.759 --> 00:03:57.719 It is. The immense tidal forces of our growing galaxy 86 00:03:57.759 --> 00:04:01.599 would literally tear the incoming dwarf galaxy apart. It is 87 00:04:01.639 --> 00:04:04.039 a complete dissolution of the original structure. 88 00:04:04.120 --> 00:04:05.960 So they don't survive the fall, not at all. 89 00:04:06.039 --> 00:04:09.879 They disperse everything they have. They're stellar populations, they're vast 90 00:04:09.960 --> 00:04:14.560 reservoirs of interstellar gas. They're halos of dark matter just 91 00:04:14.599 --> 00:04:18.439 gone violently stripped away and scattered directly into the chaotic 92 00:04:18.600 --> 00:04:21.199 swirling mass of our forming proto galaxy. 93 00:04:21.360 --> 00:04:23.519 I'm trying to picture the sheer scale of that. 94 00:04:23.879 --> 00:04:25.240 It's hard to wrap your head around. 95 00:04:25.399 --> 00:04:29.240 It's like, Okay, imagine having a sprawling metropolis, let's say 96 00:04:29.319 --> 00:04:33.680 Tokyo or London. Okay, good analogy, and this city slowly 97 00:04:33.720 --> 00:04:37.319 expands outward over the centuries. As it grows, it swallows 98 00:04:37.399 --> 00:04:41.079 up all these independent neighboring farming towns. Right, But it 99 00:04:41.079 --> 00:04:44.839 doesn't just annex them, you know. It bulldozes their town halls, 100 00:04:44.959 --> 00:04:48.920 rips up their roads, and completely disperses their populations into the. 101 00:04:48.839 --> 00:04:51.319 City grid until you can't even tell where the original 102 00:04:51.399 --> 00:04:54.160 city ended and the farming towns began exactly. 103 00:04:54.199 --> 00:04:56.879 The city just absorbs the raw materials and the people 104 00:04:57.199 --> 00:04:59.319 and completely erases the original borders. 105 00:04:59.399 --> 00:05:02.959 The structural integrity of those independent towns is just gone forever. 106 00:05:03.360 --> 00:05:05.680 Okay, let's unpack this, because here is where I really 107 00:05:05.720 --> 00:05:08.959 struggle with the whole galactic archaeology concept. 108 00:05:09.000 --> 00:05:09.759 Okay, lagh it on me. 109 00:05:10.240 --> 00:05:15.399 If the Milky Way completely shredded these smaller galaxies, if 110 00:05:15.399 --> 00:05:18.639 it pays over those farming towns and violently mixed everything 111 00:05:18.680 --> 00:05:22.040 into a metropolitan soup, right, how is it even physically 112 00:05:22.120 --> 00:05:25.519 possible to recognize what used to be a separate galaxy. 113 00:05:25.800 --> 00:05:28.160 Ah, that is the million dollar question. 114 00:05:28.399 --> 00:05:30.399 Like, if I'm looking at one hundred billion stars in 115 00:05:30.439 --> 00:05:33.839 the Milky Way, how can astronomer's point to a specific 116 00:05:33.920 --> 00:05:37.079 star and definitively say that one right there used to 117 00:05:37.079 --> 00:05:39.600 belong to a completely different ancient galaxy. 118 00:05:39.639 --> 00:05:42.639 It's a brilliant question, honestly, because looking at the Milky 119 00:05:42.639 --> 00:05:45.800 Way today, it really does just look like a homogeneous soup. 120 00:05:45.879 --> 00:05:48.079 Just a big glowing disc exactly. 121 00:05:48.639 --> 00:05:52.480 But it turns out the universe leaves indelible fingerprints. 122 00:05:52.680 --> 00:05:53.360 Fingerprints. 123 00:05:53.600 --> 00:05:58.519 Yes, the initial violent shredding destroys the galaxy's overall structure, 124 00:05:58.959 --> 00:06:02.000 but it doesn't actually just droy the individual stars themselves. 125 00:06:02.079 --> 00:06:03.839 Oh, I see, the buildings are gone, but the people 126 00:06:03.839 --> 00:06:04.680 are still walking. 127 00:06:04.480 --> 00:06:09.040 Around precisely, and astronomers hunt for these absorbed alien stars 128 00:06:09.600 --> 00:06:14.480 using two incredibly powerful, highly specific clues, which are the 129 00:06:14.480 --> 00:06:18.600 eccentricities of their galactic orbits and their chemical composition orbit 130 00:06:18.639 --> 00:06:20.319 in chemistry, orbit in chemistry. 131 00:06:20.399 --> 00:06:23.279 Okay, let's tackle the orbit first, because I think the 132 00:06:23.319 --> 00:06:25.279 common assumption, at least for me, is that all the 133 00:06:25.319 --> 00:06:28.480 stars in the Milky Way are essentially just swirling around 134 00:06:28.480 --> 00:06:32.160 the galactic center in one big, flat, orderly carousel. 135 00:06:32.399 --> 00:06:35.680 And for the vast majority of stars born natively within 136 00:06:35.720 --> 00:06:38.199 our galaxy's disc, that is generally true. 137 00:06:38.240 --> 00:06:39.480 They behave themselves, right. 138 00:06:39.519 --> 00:06:42.040 They form out of the same rotating disc of gas, 139 00:06:42.319 --> 00:06:46.160 and because of the conservation of angular momentum, they move together. 140 00:06:46.360 --> 00:06:50.519 They travel in relatively predictable circular paths around the galactic center. 141 00:06:50.759 --> 00:06:52.800 Exactly. They are the native population. 142 00:06:53.319 --> 00:06:55.680 So going back to the city thing, they are like 143 00:06:55.839 --> 00:07:00.959 cars driving smoothly along a multi lane highway. Yes, everyone 144 00:07:01.000 --> 00:07:03.199 is going the same direction, staying in their lanes, moving 145 00:07:03.199 --> 00:07:04.199 with the general flow. 146 00:07:04.040 --> 00:07:09.720 Of traffic, exactly. But when you meticulously map the billions 147 00:07:09.759 --> 00:07:12.279 of stars moving through our galaxy, which by the way, 148 00:07:12.399 --> 00:07:16.399 requires measuring not just their two dimensional position in the 149 00:07:16.439 --> 00:07:18.879 sky but their three D velocity and. 150 00:07:18.920 --> 00:07:22.079 Trajectory, which is an insane amount of data. 151 00:07:21.920 --> 00:07:24.560 It is. But when you do that you occasionally find 152 00:07:24.639 --> 00:07:29.000 glaring anomalies, like what you find stars with highly eccentric orbits. 153 00:07:29.040 --> 00:07:31.360 Now eccentric in this context doesn't mean the star has 154 00:07:31.399 --> 00:07:32.560 a quirky personality. 155 00:07:32.720 --> 00:07:35.279 No, No, we are talking about the physical geometry of 156 00:07:35.319 --> 00:07:38.800 its path, right, Instead of a nice flat circular orbit 157 00:07:38.879 --> 00:07:42.319 that stays neatly within the galactic plane, these stars are 158 00:07:42.360 --> 00:07:45.399 on wildly irregular, highly elliptical paths. 159 00:07:45.519 --> 00:07:47.160 What does that look like in three D space? 160 00:07:47.519 --> 00:07:51.040 Well, they might plunge straight down vertically through the galactic. 161 00:07:50.680 --> 00:07:53.560 Disk, just straight through the carousel exactly. 162 00:07:54.040 --> 00:07:56.920 Or they might sweep incredibly far out into the distant, 163 00:07:56.959 --> 00:08:01.480 sparse galactic halo before diving aggressive back toward the intensely 164 00:08:01.519 --> 00:08:02.240 crowded center. 165 00:08:02.560 --> 00:08:05.959 So, going back to the highway analogy, an eccentric orbit 166 00:08:06.079 --> 00:08:07.759 isn't just a car changing lanes. 167 00:08:07.839 --> 00:08:08.680 No, not at all. 168 00:08:08.759 --> 00:08:12.920 It is a car completely ignoring the existence of the road. 169 00:08:13.519 --> 00:08:17.720 It's swerving perpendicularly across the median, cutting straight through the 170 00:08:17.759 --> 00:08:18.240 flow of. 171 00:08:18.199 --> 00:08:21.879 Traffic, completely disconnected from the direction everyone else is traveling. 172 00:08:21.959 --> 00:08:24.560 That is terrifying, right, And if you see a vehicle 173 00:08:24.600 --> 00:08:27.879 doing that on a highway, your immediate logical conclusion is 174 00:08:27.920 --> 00:08:30.560 that the car didn't merge onto this road normally. 175 00:08:30.720 --> 00:08:33.720 It definitely didn't accelerate down the on ramp exactly. 176 00:08:33.879 --> 00:08:36.919 Something must have violently thrown it across the lanes. A crash, 177 00:08:37.039 --> 00:08:41.120 a cosmic crash. In galactic kinematics, a highly eccentric orbit 178 00:08:41.320 --> 00:08:46.159 is the lingering kinetic scar of an ancient outside collision. Wow, 179 00:08:46.200 --> 00:08:48.840 what's fascinating here is that it is a dead giveaway 180 00:08:49.240 --> 00:08:52.600 that the star did not originate from the peaceful native disk. 181 00:08:53.000 --> 00:08:56.399 The scale of that investigation is staggering to me. You 182 00:08:56.480 --> 00:08:59.360 are literally looking at a catalog of billions of moving 183 00:08:59.399 --> 00:09:02.679 points of life billions. Yeah, trying to isolate the few 184 00:09:02.720 --> 00:09:04.440 dozen that are driving across the median. 185 00:09:04.639 --> 00:09:06.360 It takes meticulous patients. 186 00:09:06.480 --> 00:09:08.279 You have to track their current x, y, and z 187 00:09:08.399 --> 00:09:12.200 coordinates in a three dimensional map of space, measure their 188 00:09:12.320 --> 00:09:16.799 radio velocity, and then what rewind their mathematical packs millions 189 00:09:16.840 --> 00:09:18.320 of years into the past just to. 190 00:09:18.240 --> 00:09:21.480 See where they came from. Yes, the kinematic mapping is 191 00:09:21.519 --> 00:09:24.240 a monumental achievement in modern astronomy. 192 00:09:24.320 --> 00:09:26.639 But wait, didn't you say orbit was only one clue 193 00:09:26.679 --> 00:09:27.120 I did? 194 00:09:27.679 --> 00:09:29.720 Orbit alone isn't enough to secure a conviction? 195 00:09:30.320 --> 00:09:33.559 Why not? If a star is plunging vertically through the disc, 196 00:09:33.879 --> 00:09:36.320 isn't that proof enough that it's an alien interloper? 197 00:09:36.480 --> 00:09:40.480 Well not necessarily, Yeah, no, because a native star could 198 00:09:40.559 --> 00:09:44.399 theoretically be violently kicked into a bizarre orbit by a 199 00:09:44.480 --> 00:09:46.360 localized internal event. 200 00:09:46.240 --> 00:09:48.759 Oh like a domestic dispute instead of a foreign invasion. 201 00:09:48.919 --> 00:09:51.039 That's a great way to put it, like a nearby 202 00:09:51.080 --> 00:09:55.559 supernova explosion could blast a native star off course, right, 203 00:09:55.759 --> 00:10:00.120 or a gravitational interaction with a passing giant molecular. 204 00:09:59.600 --> 00:10:01.960 Cloud or a black hole, or a. 205 00:10:01.879 --> 00:10:05.279 Close encounter with a black hole exactly any of those 206 00:10:05.279 --> 00:10:08.000 could disrupt a native star's circular path. 207 00:10:08.159 --> 00:10:10.799 Okay, so a weird orbit makes it a suspect, but 208 00:10:11.039 --> 00:10:12.519 not definitely guilty. 209 00:10:12.559 --> 00:10:17.320 Exactly. So to definitively prove a star is an alien 210 00:10:17.399 --> 00:10:21.320 artifact from a consumed dwarf galaxy like Loki, that wild 211 00:10:21.399 --> 00:10:24.480 orbit has to be paired with our second clue. 212 00:10:24.120 --> 00:10:25.320 The chemical forensics. 213 00:10:25.440 --> 00:10:26.919 The chemical forensics, right. 214 00:10:26.840 --> 00:10:30.919 The chemistry, and to understand why chemical forensics can identify 215 00:10:30.960 --> 00:10:33.720 a star as an ancient outsider, I feel like we 216 00:10:33.759 --> 00:10:34.759 need to take a detour. 217 00:10:34.919 --> 00:10:35.440 Let's do it. 218 00:10:35.480 --> 00:10:37.960 We need to look at the universe's heavy metal forges, 219 00:10:38.200 --> 00:10:40.279 because it's not just about what elements are in. 220 00:10:40.240 --> 00:10:42.639 The star, right, It's about what elements aren't. 221 00:10:42.399 --> 00:10:45.240 There, which brings us to stellar nuclear synthesis. 222 00:10:45.440 --> 00:10:47.759 It does. It is the fundamental process by which the 223 00:10:47.840 --> 00:10:49.679 universe creates the periodic table. 224 00:10:49.840 --> 00:10:52.679 Okay, let's bypass the absolute basics here, because we know 225 00:10:52.759 --> 00:10:55.279 the early universe was just hydrogen. 226 00:10:54.840 --> 00:10:57.879 And helium, just a very boring, simple soup. 227 00:10:57.799 --> 00:11:01.159 Right, And we know stars act as fusion actors, But 228 00:11:01.279 --> 00:11:04.759 the concept of chemical generations is what matters here, right. 229 00:11:04.679 --> 00:11:07.360 Yes, the generational aspect is crucial. 230 00:11:07.720 --> 00:11:10.120 So the universe essentially has a family tree. 231 00:11:10.480 --> 00:11:15.480 Exactly. Think about the very first generation of stars that ignited. 232 00:11:15.039 --> 00:11:17.639 In the cosmos, the granddaddies. 233 00:11:16.919 --> 00:11:20.120 The Granddaddy's of the universe. They were forged purely out 234 00:11:20.159 --> 00:11:24.799 of pristine, primordial hydrogen and helium. There was nothing else available. 235 00:11:25.480 --> 00:11:28.759 And these stars were massive. They burned fast, and when 236 00:11:28.759 --> 00:11:32.200 they died, they died in violent supernova explosions. And when 237 00:11:32.200 --> 00:11:36.919 they exploded, they blasted newly forged heavier elements things they 238 00:11:36.960 --> 00:11:39.840 cooked up in their cores, like carbon, oxygen, and iron, 239 00:11:39.919 --> 00:11:41.679 out into the surrounding gas clouds. 240 00:11:42.159 --> 00:11:45.159 So they basically seeded the surrounding space with a brand 241 00:11:45.240 --> 00:11:46.440 new recipe of elements. 242 00:11:46.519 --> 00:11:48.440 They did they polluted the pristine gas. 243 00:11:48.720 --> 00:11:51.360 So the next generation of stars that formed out of 244 00:11:51.360 --> 00:11:54.960 those enriched gas clouds inherited a tiny fraction of those 245 00:11:54.960 --> 00:11:55.840 heavier elements. 246 00:11:55.960 --> 00:11:59.360 Exactly. They started life with a slightly more complex chemical 247 00:11:59.399 --> 00:12:00.200 makeup of. 248 00:12:00.200 --> 00:12:04.840 Their lives fused even heavier elements exploded and handed an 249 00:12:04.840 --> 00:12:07.799 even richer chemical cocktail down to the third generation. 250 00:12:08.080 --> 00:12:12.159 It is an ongoing multi billion year cosmic recycling program. 251 00:12:12.440 --> 00:12:14.759 Every generation gets more chemically complex. 252 00:12:15.200 --> 00:12:18.679 Our sun is a beneficiary of this recycling rye a 253 00:12:18.799 --> 00:12:19.639 huge beneficiary. 254 00:12:19.679 --> 00:12:21.720 It's a relatively late generation. 255 00:12:21.440 --> 00:12:24.120 Star, which is why if you look at its chemical spectrum, 256 00:12:24.360 --> 00:12:26.440 it is loaded with heavier elements. 257 00:12:26.080 --> 00:12:30.879 Exactly, But astronomers use a specific, somewhat idiosyncratic terminology to 258 00:12:30.960 --> 00:12:31.480 describe this. 259 00:12:31.840 --> 00:12:33.200 Oh no, what do they call it? 260 00:12:33.360 --> 00:12:37.240 Well, in astrophysics, anything heavier than helium on the periodic 261 00:12:37.279 --> 00:12:40.360 table is simply referred to as a metal, which. 262 00:12:40.120 --> 00:12:43.960 Is completely wild. No, I know, like to a chemist, 263 00:12:44.320 --> 00:12:49.120 calling oxygen or neon a metal is grounds for having 264 00:12:49.200 --> 00:12:50.159 your degree revoked. 265 00:12:50.200 --> 00:12:52.919 Oh it drives chemists absolutely crazy, But for us, it 266 00:12:52.960 --> 00:12:54.720 gives us a vital shorthand. 267 00:12:54.879 --> 00:12:57.600 Okay, so if everything heavier than helium is a metal, 268 00:12:57.879 --> 00:12:59.840 how does that help us find old stars? 269 00:13:00.240 --> 00:13:03.559 Because astronomers refer to stars with relatively small amounts of 270 00:13:03.600 --> 00:13:07.960 these heavier elements, specifically elements like iron, as metal. 271 00:13:07.639 --> 00:13:10.879 Poor, metal poor. So what does this all mean for 272 00:13:10.919 --> 00:13:11.720 our investigation? 273 00:13:11.919 --> 00:13:14.679 Well, this is the crux of the chemical fingerprint, because 274 00:13:14.679 --> 00:13:17.879 if you find a star that is extremely metal poor. 275 00:13:17.840 --> 00:13:20.519 It means it didn't get the good stuff exactly. 276 00:13:20.799 --> 00:13:23.679 It means it did not have the benefit of many 277 00:13:23.919 --> 00:13:26.759 previous generations of cosmic orcyclice. 278 00:13:26.840 --> 00:13:28.200 So it must be incredibly old. 279 00:13:28.320 --> 00:13:31.000 It must have formed very very early in the universe's 280 00:13:31.039 --> 00:13:34.240 history out of gas that was still mostly pristine. 281 00:13:34.440 --> 00:13:37.960 That is so cool. An extremely metal poor star is 282 00:13:38.080 --> 00:13:40.279 essentially a rough draft of a star. 283 00:13:40.440 --> 00:13:43.639 A rough draft. Yes, it is a literal fossil from 284 00:13:43.679 --> 00:13:46.639 the dawn of time, sitting right there in our galaxy, 285 00:13:47.120 --> 00:13:51.080 virtually untouched by the billions of years of chemical evolution 286 00:13:51.200 --> 00:13:52.559 that happened everywhere else. 287 00:13:52.759 --> 00:13:53.039 Wow. 288 00:13:53.200 --> 00:13:56.799 And those early metal poor dwarf galaxies were the exact 289 00:13:57.240 --> 00:14:00.000 raw materials that merged together to form the massive gas 290 00:14:00.000 --> 00:14:01.120 galaxies we see today. 291 00:14:01.200 --> 00:14:04.039 Okay, so we have the two pieces of our forensic toolkit. 292 00:14:04.120 --> 00:14:04.480 We do. 293 00:14:04.720 --> 00:14:08.559 We are hunting for ancient fossilized metal poor stars, and 294 00:14:08.600 --> 00:14:11.080 we need them to be flying around of bizarre, highly 295 00:14:11.120 --> 00:14:14.039 eccentric orbits. Check. The next hurdle, though, is the sheer 296 00:14:14.080 --> 00:14:15.480 geography of the Milky Way. 297 00:14:15.519 --> 00:14:16.399 The spatial problem. 298 00:14:16.519 --> 00:14:19.200 Yes, where do you even begin sweeping for them? The 299 00:14:19.279 --> 00:14:22.480 galaxy is one hundred thousand light years across. 300 00:14:22.159 --> 00:14:26.559 Right, and geography and timing are intrinsically linked in galaxy formation. Well, 301 00:14:26.919 --> 00:14:29.759 if we consider the timeline of how the Milky Way 302 00:14:29.799 --> 00:14:34.799 was assembled, those earliest building blocks, those ancient metal poor 303 00:14:35.240 --> 00:14:39.879 dwarf galaxies like Loki, they merged into the forming proto 304 00:14:39.960 --> 00:14:42.159 galaxy at the very beginning of the process. 305 00:14:42.240 --> 00:14:43.919 They were the first bricks in the foundation. 306 00:14:44.240 --> 00:14:47.480 Right. And because they were drawn into the gravitational well 307 00:14:47.600 --> 00:14:51.919 so early, the remnants of those systems, they're dispersed. 308 00:14:51.440 --> 00:14:53.399 Stars should logically sink toward the bottom. 309 00:14:53.639 --> 00:14:56.840 Exactly, they should populate the deepest inner regions of the 310 00:14:56.840 --> 00:14:59.919 Milky Way. They should be trapped in the dense core 311 00:15:00.080 --> 00:15:03.960 or what we call the galactic bulge, and deeply embedded 312 00:15:04.000 --> 00:15:05.799 within the inner galactic plane. 313 00:15:05.840 --> 00:15:08.799 That makes perfect physical sense. The material that falls in 314 00:15:08.960 --> 00:15:11.759 first ends up clustered in the middle under the weight 315 00:15:11.799 --> 00:15:14.120 of everything that piles on top of it later. 316 00:15:14.320 --> 00:15:16.039 It's just gravity doing its job. 317 00:15:16.279 --> 00:15:19.840 Conversely, the dwarf galaxies that were consumed much later on, 318 00:15:20.039 --> 00:15:22.080 long after the main structure of the Milky Way was 319 00:15:22.120 --> 00:15:25.000 already spinning, they would likely be scattered out in the 320 00:15:25.080 --> 00:15:27.080 expansive spherical outer. 321 00:15:26.960 --> 00:15:29.440 Halo because they couldn't penetrate as deeply. 322 00:15:29.679 --> 00:15:33.360 So the geographical rule of thumb should be early building 323 00:15:33.399 --> 00:15:37.480 blocks and the dense inner plane late arrivals scattered in 324 00:15:37.519 --> 00:15:38.639 the sparse outer halo. 325 00:15:38.759 --> 00:15:39.919 That was the standard model. 326 00:15:40.000 --> 00:15:42.679 Yes, but I hear a butt coming. 327 00:15:42.480 --> 00:15:46.879 Oh, a massive butt. When astronomers actually conducted massive surveys 328 00:15:46.879 --> 00:15:50.879 of the galaxy looking for these extremely metal poor stars, 329 00:15:51.399 --> 00:15:54.399 they ran headfirst into a massive, frustrating anomaly. 330 00:15:55.080 --> 00:15:57.240 The map didn't match the territory at all. 331 00:15:57.080 --> 00:15:57.840 Not even slightly. 332 00:15:58.080 --> 00:15:58.799 What did they find. 333 00:15:59.080 --> 00:16:03.360 Well, they found very much metal poor star, sure, but frustratingly, 334 00:16:03.720 --> 00:16:06.120 almost all of them were being found far out in 335 00:16:06.120 --> 00:16:10.159 the outer halo. Wait what Yeah, astronomers were desperately searching 336 00:16:10.200 --> 00:16:13.720 the inner galactic plane, where the oldest building blocks fundamentally 337 00:16:13.759 --> 00:16:16.200 should be, and they just weren't finding them, not. 338 00:16:16.120 --> 00:16:19.440 In the numbers that their hierarchical models predicted exactly. 339 00:16:19.519 --> 00:16:20.600 It was a severe mismatch. 340 00:16:20.679 --> 00:16:24.480 It's like, Okay, imagine excavating the foundation of an ancient ruin. Okay, 341 00:16:24.639 --> 00:16:27.799 you dig down expecting to find Roman bricks, but you 342 00:16:27.879 --> 00:16:32.320 find absolutely nothing but modern concrete. And then you realize 343 00:16:32.679 --> 00:16:37.399 all the oldest original Roman bricks are inexplicably scattered out 344 00:16:37.440 --> 00:16:40.399 in the surrounding grassy fields miles away. 345 00:16:40.559 --> 00:16:43.519 It completely upends the logic of how the structure was built. 346 00:16:43.639 --> 00:16:44.559 It makes no sense. 347 00:16:44.639 --> 00:16:48.679 It was a literal crisis for galactic archaeologists, and it 348 00:16:48.840 --> 00:16:51.919 forced the scientific community to start making some very complex, 349 00:16:52.120 --> 00:16:56.200 somewhat strain assumptions to explain the discrepancy. 350 00:16:56.360 --> 00:16:59.039 Because scientists hate a vacuum, we really do. 351 00:16:59.360 --> 00:17:00.960 We need an explanations. 352 00:17:01.039 --> 00:17:02.480 So what was the strained assumption. 353 00:17:03.000 --> 00:17:06.079 Well, astronomers noticed that the few metal poor stars they 354 00:17:06.119 --> 00:17:09.240 did manage to find deep in the galactic plane often 355 00:17:09.240 --> 00:17:10.640 had retrograde orbits. 356 00:17:11.000 --> 00:17:15.200 Retrograde meaning they are orbiting the center of the galaxy backward. Yes, 357 00:17:15.359 --> 00:17:18.640 they're moving in complete opposition to the general rotational flow 358 00:17:18.720 --> 00:17:19.640 of the Milky Way's. 359 00:17:19.519 --> 00:17:23.359 Disc exactly so, because they needed an explanation for why 360 00:17:23.400 --> 00:17:26.119 these ancient stores were so rare in the plane, the 361 00:17:26.160 --> 00:17:29.000 prevailing theory became that retrograde stars in the plane were 362 00:17:29.039 --> 00:17:32.559 the true rare remnants of early violent assembly. 363 00:17:32.359 --> 00:17:34.119 Because you'd have to hit the galaxy pretty hard to 364 00:17:34.200 --> 00:17:35.160 end up going backwards. 365 00:17:35.440 --> 00:17:38.200 That was the logic. The idea was that an early 366 00:17:38.240 --> 00:17:41.359 merger would be chaotic and violent enough to throw the 367 00:17:41.400 --> 00:17:43.079 consumed stars into reverse. 368 00:17:43.400 --> 00:17:45.400 Okay, and what about the ones going forward? 369 00:17:45.839 --> 00:17:51.599 Oh? Meanwhile, pro grade stars, the ones moving forward harmoniously 370 00:17:51.640 --> 00:17:54.519 with the disc's rotation, were assumed to have been added 371 00:17:54.599 --> 00:17:58.880 much later by gentler accretion events that just naturally aligned 372 00:17:58.880 --> 00:17:59.759 with the spinning disk. 373 00:18:00.000 --> 00:18:02.880 Wow, So they were basically forcing the puzzle pieces together 374 00:18:02.920 --> 00:18:04.240 because they didn't have enough data. 375 00:18:04.279 --> 00:18:07.400 They absolutely were. They looked at the few retrograde stars 376 00:18:07.440 --> 00:18:10.160 they found and essentially declared a universal rule. 377 00:18:10.359 --> 00:18:13.880 Prograde means one type of origin. Retrograde means a completely 378 00:18:13.880 --> 00:18:14.839 different type of origin. 379 00:18:15.039 --> 00:18:18.519 Exactly, they assumed you couldn't possibly have forward moving and 380 00:18:18.599 --> 00:18:22.480 backward moving ancient stars originating from the same early event. 381 00:18:22.599 --> 00:18:24.400 They thought it was physically impossible. 382 00:18:24.480 --> 00:18:28.759 The assumption was incredibly rigid. Prograde and retrograde meant totally 383 00:18:28.799 --> 00:18:31.720 different epochs and completely different progenitor galaxies. 384 00:18:31.920 --> 00:18:36.039 And that rigid assumption that forced geographic disconnect is exactly 385 00:18:36.079 --> 00:18:40.079 what makes this new study by Federico Ccido and his 386 00:18:40.200 --> 00:18:43.640 team so monumental. It really is because they didn't just 387 00:18:43.720 --> 00:18:47.000 find a missing puzzle piece. They found a puzzle piece 388 00:18:47.200 --> 00:18:50.799 that completely breaks the previous picture of how our galaxy 389 00:18:50.839 --> 00:18:51.319 was built. 390 00:18:51.519 --> 00:18:56.720 It is a remarkable paradigm shifting finding. Cistito's team focused 391 00:18:56.720 --> 00:19:01.200 specifically on sweeping the Milky Way's galactic plane, using highly 392 00:19:01.240 --> 00:19:03.680 advanced spectroscopic surveys. 393 00:19:03.279 --> 00:19:04.880 Looking deep in the concrete foundation. 394 00:19:05.119 --> 00:19:09.000 Exactly and against the odds of all previous searches, they 395 00:19:09.039 --> 00:19:13.359 successfully isolated a sample of twenty strictly metal poor stars 396 00:19:13.440 --> 00:19:15.519 located right there, deep in the plane. 397 00:19:15.680 --> 00:19:21.440 Twenty ancient heavy metal deficient fossil stars, yes, existing exactly 398 00:19:21.519 --> 00:19:24.519 where the original gravitational theory said they should be, but 399 00:19:24.599 --> 00:19:27.759 where actual observational surveys had previously failed to find them. 400 00:19:27.799 --> 00:19:29.680 Finding them at all was a massive triumph. 401 00:19:29.720 --> 00:19:31.839