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 Astronomy 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 --> 00:00:26.879 slumber under the night sky. 7 00:00:26.960 --> 00:00:29.839 If you look up at the Andromeda galaxy tonight, you're 8 00:00:29.879 --> 00:00:32.119 actually looking at a completely incomplete map. 9 00:00:32.320 --> 00:00:35.079 Yeah, totally incomplete. We miss so much of what's. 10 00:00:34.920 --> 00:00:38.960 Actually there, right because just recently on March thirtieth, twenty 11 00:00:39.039 --> 00:00:44.359 twenty six, astronomers announced this incredible update to our cosmic backyard. 12 00:00:44.679 --> 00:00:47.399 It's honestly one of the most fascinating finds in recent years. 13 00:00:47.600 --> 00:00:51.039 It really is. They found an entirely new galaxy hiding 14 00:00:51.240 --> 00:00:55.240 right there, orbiting Andromeda, not you know, billions of light 15 00:00:55.320 --> 00:00:57.799 years away at the edge of the universe, but literally 16 00:00:57.880 --> 00:00:58.679 right next door. 17 00:00:58.840 --> 00:01:02.960 And the kicker is are billion dollars supercomputers and all 18 00:01:03.000 --> 00:01:06.319 those advanced algorithms they entirely missed it. 19 00:01:06.239 --> 00:01:08.200 Which is wild. But before we get into that, I mean, 20 00:01:08.439 --> 00:01:11.079 new galaxy is a phrase we need to handle carefully, right. 21 00:01:11.120 --> 00:01:14.480 Oh absolutely. When people hear new galaxy, it immediately brings 22 00:01:14.480 --> 00:01:19.120 to mind like sweeping spiral arms, glowing pink nebulas, supermassive. 23 00:01:18.519 --> 00:01:21.920 Black holes, like the classic Hubble desktop backgrounds exactly. 24 00:01:22.519 --> 00:01:26.319 But this newly discovered object, officially designated Andromeda X six 25 00:01:26.400 --> 00:01:30.480 six or nxx six for short, is the absolute antithesis 26 00:01:30.599 --> 00:01:31.879 of that majestic imagery. 27 00:01:32.159 --> 00:01:33.719 So what are we actually looking at here? 28 00:01:33.840 --> 00:01:36.359 Well, we classify it as an ultra faint dwarf galaxy 29 00:01:36.400 --> 00:01:41.959 a UFD. It's a tiny, incredibly elusive and just profoundly 30 00:01:42.040 --> 00:01:42.959 ancient system. 31 00:01:43.079 --> 00:01:43.239 Right. 32 00:01:43.280 --> 00:01:45.280 It's less of a shiny metropolis and more of a 33 00:01:46.120 --> 00:01:48.760 cosmic ghost wandering through Andromeda's halo. 34 00:01:49.120 --> 00:01:51.599 A ghost is the perfect way to describe it. And 35 00:01:51.640 --> 00:01:53.760 we aren't just going to list off coordinates for a 36 00:01:53.799 --> 00:01:54.920 new speck in this guy. 37 00:01:54.760 --> 00:01:57.680 Today, no, because the reason this faint little ghost matters 38 00:01:57.719 --> 00:01:59.920 to you listening right now is that it's essentially a 39 00:02:00.200 --> 00:02:01.400 cosmic time machine. 40 00:02:01.519 --> 00:02:05.359 Yeah. It operates as this pristine, untouched laboratory for the 41 00:02:05.439 --> 00:02:08.639 universe's most mysterious substance, which is dark. 42 00:02:08.479 --> 00:02:11.719 Matter, and understanding how it was found requires looking at 43 00:02:11.719 --> 00:02:13.960 the sheer power of the human eye, even in an 44 00:02:14.000 --> 00:02:16.719 era totally dominated by artificial intelligence. 45 00:02:17.000 --> 00:02:19.439 What makes an object so small capable of answering the 46 00:02:19.439 --> 00:02:23.639 biggest questions in physics is it's extreme nature. It's a 47 00:02:23.680 --> 00:02:27.039 tiny size and profound faintness. Hold the real. 48 00:02:26.840 --> 00:02:31.000 Secrets, because massive galaxies are just too chaotic exactly. 49 00:02:30.560 --> 00:02:33.840 They're noisy, but tiny dead systems like this one offer 50 00:02:33.879 --> 00:02:37.319 a completely clean environment to observe fundamental physics at work. 51 00:02:37.599 --> 00:02:40.120 Okay, so let's figure out what it actually means to 52 00:02:40.120 --> 00:02:44.080 be an ultra faint dwarf galaxy. Just how small and 53 00:02:44.159 --> 00:02:46.680 how dim does a collection of stars have to be 54 00:02:46.800 --> 00:02:47.919 to get that classification? 55 00:02:48.639 --> 00:02:54.280 Well, geographically speaking, and sits about two point five to 56 00:02:54.360 --> 00:02:56.319 three million light years away from. 57 00:02:56.120 --> 00:03:00.439 Earth, which puts it squarely in the local group our neighborhood, right, But. 58 00:03:00.479 --> 00:03:03.319 The really vital measurement is its distance from the center 59 00:03:03.360 --> 00:03:06.960 of the Andromeda galaxy itself, which clocks in at roughly 60 00:03:07.000 --> 00:03:09.000 three hundred and eighty eight thousand light years. 61 00:03:09.400 --> 00:03:11.560 That sounds like a massive distance. I mean, that's farther 62 00:03:11.639 --> 00:03:13.439 than the Moon is from the Earth. If you scale 63 00:03:13.479 --> 00:03:14.520 it up to glact. 64 00:03:14.280 --> 00:03:17.800 Proportions, it does sound distant, but in galactic physics it 65 00:03:17.879 --> 00:03:23.039 sits deep within Andromeda's gravitational grip. Atrophysicists use this metric 66 00:03:23.120 --> 00:03:24.159 called the virial. 67 00:03:23.919 --> 00:03:26.520 Radius, the virial radio. Okay, break that down for us. 68 00:03:26.759 --> 00:03:29.120 You can think of the virial radius as the ultimate 69 00:03:29.120 --> 00:03:31.840 boundary line of a galaxy's gravitational dominance. 70 00:03:31.919 --> 00:03:34.039 So it's like the city limits of its gravity. 71 00:03:34.120 --> 00:03:37.280 Yeah, exactly. It's the sphere of influence where the larger 72 00:03:37.319 --> 00:03:40.840 galaxies gravity dictates the motion of everything inside it, rather 73 00:03:40.879 --> 00:03:43.199 than the expansion of the universe pulling things apart. 74 00:03:43.360 --> 00:03:46.800 And what's the virial radius for a giant spiral like Andromeda? 75 00:03:46.919 --> 00:03:51.400 For Andromeda, that radius extends outward to roughly eight hundred 76 00:03:51.439 --> 00:03:52.759 and fifty thousand light years. 77 00:03:52.960 --> 00:03:55.439 Oh wow, So at three hundred and eighty eight thousand 78 00:03:55.479 --> 00:03:59.879 light years, and XXI six is well within the city. 79 00:03:59.680 --> 00:04:03.080 Limits, firmly within the suburbs. Yeah, it is securely and 80 00:04:03.159 --> 00:04:06.400 permanently a gravitationally bound satellite of Andromeda. 81 00:04:06.520 --> 00:04:09.960 It's just orbiting the larger galaxy, locked in this cosmic bands, 82 00:04:10.120 --> 00:04:13.439 governed entirely by Andromeda's immense mass, exactly. 83 00:04:13.479 --> 00:04:16.240 So it's locked in. But the sheer compactness of this 84 00:04:16.360 --> 00:04:17.920 object is what really dons. 85 00:04:17.639 --> 00:04:19.879 The mind Yeah, the measurements show it has a half 86 00:04:19.920 --> 00:04:22.480 light radius of just two hundred and eight light years. 87 00:04:22.240 --> 00:04:23.639 Which is incredibly tiny. 88 00:04:23.720 --> 00:04:25.920 I mean, our Milky Way is roughly one hundred thousand 89 00:04:26.000 --> 00:04:28.399 light years across. This entire new galaxy is just a 90 00:04:28.399 --> 00:04:29.399 couple of hundred light. 91 00:04:29.360 --> 00:04:30.800 Years wide, barely a blip. 92 00:04:30.839 --> 00:04:32.879 I do need to stop right there, though, because half 93 00:04:32.920 --> 00:04:35.120 light radius is sort of a weird term. Why don't 94 00:04:35.199 --> 00:04:37.480 astronomers just measure from the center to the edge. 95 00:04:37.519 --> 00:04:40.439 Well, because galaxies do not have hard, sharp edges like 96 00:04:40.480 --> 00:04:42.279 a planet or a table. 97 00:04:42.040 --> 00:04:43.279 Right, they kind of just fade out. 98 00:04:43.480 --> 00:04:46.240 Yeah, there are diffuse clouds of stars. They gradually thin 99 00:04:46.279 --> 00:04:48.800 out into nothingness. Yeah, if you try to measure to 100 00:04:48.839 --> 00:04:53.639 the absolute outermost star, you get wildly inconsistent results. 101 00:04:53.279 --> 00:04:55.720 Because it just depends on how sensitive your telescope is. 102 00:04:55.920 --> 00:04:59.759 Very sisely, Instead, astronomers use the half light radius. It's 103 00:04:59.800 --> 00:05:03.399 the distance from the core, within which exactly fifty percent 104 00:05:03.439 --> 00:05:05.319 of the galaxy's total light is emitted. 105 00:05:05.439 --> 00:05:09.279 Got it. So it provides a robust, mathematically consistent way 106 00:05:09.360 --> 00:05:13.439 to define the bulk of this fuzzy edgeless object exactly. 107 00:05:13.480 --> 00:05:15.720 So the core, the main glowing heart of this thing, 108 00:05:16.319 --> 00:05:18.680 is only two hundred and eight light years across. That's 109 00:05:18.680 --> 00:05:20.680 about sixty four parsex. 110 00:05:20.279 --> 00:05:23.720 And I was reading that its structure is unusually uniform too. 111 00:05:23.720 --> 00:05:26.800 It is. We measure the shape of these objects using ellipticity. 112 00:05:27.240 --> 00:05:29.680 A perfect circle has an ellipticity. 113 00:05:29.040 --> 00:05:32.319 Of zero, and a highly stretched like cigar like oval 114 00:05:32.360 --> 00:05:33.360 would be closer to one. 115 00:05:33.519 --> 00:05:36.360 Right, and XXC six has an ellipticity of abouto points 116 00:05:36.480 --> 00:05:37.000 zero one. 117 00:05:37.079 --> 00:05:39.319 Five, So it's virtually a perfect sphere. 118 00:05:39.399 --> 00:05:42.079 It is remarkably spherical. It makes it potentially the second 119 00:05:42.079 --> 00:05:45.839 most compact ultra faint dwarf satellite ever found orbiting Andromeda. 120 00:05:45.959 --> 00:05:48.920 Wow. And then we get to the brightness, or I 121 00:05:48.920 --> 00:05:50.600 guess the complete lack of brightness. 122 00:05:50.920 --> 00:05:52.480 Yeah, it's staggeringly dim. 123 00:05:52.720 --> 00:05:56.000 The data gives it an absolute visual magnitude of roughly 124 00:05:56.160 --> 00:06:00.199 negative six point zero, and the astronomical magnitude scale is 125 00:06:00.279 --> 00:06:01.720 notoriously counterintuitive. 126 00:06:01.759 --> 00:06:02.759 Oh, it's totally backwards. 127 00:06:03.000 --> 00:06:06.319 The lower or more negative the number, the brighter the object. Right, 128 00:06:06.399 --> 00:06:08.959 our sun sits at around negative twenty six, and. 129 00:06:08.920 --> 00:06:11.079 The full moon is around negative thirteen. 130 00:06:10.959 --> 00:06:14.040 So a whole galaxy sitting at negative six is just 131 00:06:14.240 --> 00:06:18.879 profoundly dim. It's like a single dimly lit neighborhood out 132 00:06:18.920 --> 00:06:21.680 in the countryside trying to be seen next to the 133 00:06:21.720 --> 00:06:24.680 glaring neon lights of a megacity, and. 134 00:06:24.600 --> 00:06:31.480 That megacity being Andromeda. That visual illustrates the detection problem perfectly, honestly. 135 00:06:31.079 --> 00:06:34.040 Because its intrinsic light is just entirely washed out by 136 00:06:34.040 --> 00:06:35.480 the larger galaxy, washed. 137 00:06:35.279 --> 00:06:37.720 Out by the glare, and the vast distance is involved, 138 00:06:37.959 --> 00:06:41.199 it barely registers against the background static of the cosmos. 139 00:06:41.240 --> 00:06:43.720 Well wait, if it is so incredibly small, just two 140 00:06:43.839 --> 00:06:47.800 hundred something light years across and unfathomably dim, why are 141 00:06:47.839 --> 00:06:50.079 we even classifying this as a galaxy? 142 00:06:50.240 --> 00:06:51.800 That's a great question, because. 143 00:06:51.560 --> 00:06:54.680 There are globular clusters out there, these tight spheres of 144 00:06:54.759 --> 00:06:57.399 thousands of stars that are way brighter and denser than this. 145 00:06:57.839 --> 00:07:01.680 Why does an X six six get the prestigious title 146 00:07:01.759 --> 00:07:05.360 of galaxy instead of just being a random rogue star cluster. 147 00:07:05.720 --> 00:07:08.480 The distinction between a star cluster and a dwarf galaxy 148 00:07:08.800 --> 00:07:11.519 is one of the most crucial concepts in modern astronomy, 149 00:07:12.079 --> 00:07:13.920 and it actually has nothing to do with size or 150 00:07:13.959 --> 00:07:14.519 star count. 151 00:07:14.600 --> 00:07:16.160 Oh really, what does it come down to? 152 00:07:16.279 --> 00:07:20.040 Then it comes down to invisible mass. A globular cluster 153 00:07:20.399 --> 00:07:24.120 is a collection of stars, gas, and dust held together 154 00:07:24.279 --> 00:07:26.439 exclusively by their own mutual gravity. 155 00:07:26.519 --> 00:07:28.480 So what you see is what you get exactly. 156 00:07:28.879 --> 00:07:31.240 If you add up the mass of all the glowing 157 00:07:31.319 --> 00:07:34.920 stars in a globular cluster, it perfectly accounts for the 158 00:07:34.959 --> 00:07:37.240 gravitational glue holding the whole structure together. 159 00:07:37.279 --> 00:07:38.839 No hidden variables, none at all. 160 00:07:39.160 --> 00:07:42.600 But a galaxy, even an ultra fane dwarf like six, 161 00:07:42.680 --> 00:07:44.480 is fundamentally dark matter dominated. 162 00:07:44.519 --> 00:07:47.800 Okay, So it's essentially a massive invisible halo of dark 163 00:07:47.839 --> 00:07:50.120 matter that just happens to have a few stars sprinkled 164 00:07:50.120 --> 00:07:51.240 in the very center of it. 165 00:07:51.279 --> 00:07:53.800 That's exactly it. The stars are merely the glowing paint 166 00:07:53.920 --> 00:07:56.319 on a much larger invisible structural foundation. 167 00:07:56.680 --> 00:08:00.439 That's wild. So when astronomers analyze the dynamics of these objects, 168 00:08:00.759 --> 00:08:03.720 the visible matter is basically negligible. 169 00:08:03.360 --> 00:08:08.279 Completely negligible. Without a massive dark matter halo, the galaxy 170 00:08:08.279 --> 00:08:11.959 would simply fly apart. That halo is the defining signature. 171 00:08:12.240 --> 00:08:14.000 If it has a halo, it's a galaxy. 172 00:08:14.319 --> 00:08:16.839 So its dimness isn't a sign that it failed at 173 00:08:16.879 --> 00:08:18.879 being a galaxy. It's not like a star cluster that 174 00:08:19.040 --> 00:08:19.639 just gave up. 175 00:08:19.839 --> 00:08:22.800 No, not at all. The dimness is an artifact of 176 00:08:22.839 --> 00:08:26.360 extreme age, which really brings us to the origins of 177 00:08:26.360 --> 00:08:27.639 this object, right, because. 178 00:08:27.399 --> 00:08:30.639 We aren't looking at a dynamic evolving system here, we 179 00:08:30.680 --> 00:08:31.439 are looking at. 180 00:08:31.279 --> 00:08:34.919 A fossil, a literal cosmic fossil. The estimated age of 181 00:08:34.960 --> 00:08:38.679 the stars in EXI six and Exiscitos is roughly twelve 182 00:08:38.679 --> 00:08:40.279 point five billion years. 183 00:08:40.480 --> 00:08:43.840 The universe itself is only thirteen point eight billion years old, 184 00:08:43.919 --> 00:08:47.000 so the star is in this tiny smudge formed shortly 185 00:08:47.039 --> 00:08:48.279 after the Big Bang itself. 186 00:08:48.320 --> 00:08:50.600 They were among the very first generations of stars to 187 00:08:50.679 --> 00:08:51.679 light up the cosmos. 188 00:08:51.759 --> 00:08:53.759 So what happened to it? Why did it stop growing? 189 00:08:54.039 --> 00:08:57.120 Systems of this nature are referred to as reionization fossils. 190 00:08:57.480 --> 00:08:59.480 To grasp the mechanics of that, you have to picture 191 00:08:59.480 --> 00:09:01.000 the universe during its infancy. 192 00:09:01.080 --> 00:09:03.399 Okay, setting the scene for several hundred. 193 00:09:03.080 --> 00:09:05.960 Million years following the Big Bang, the universe was filled 194 00:09:06.000 --> 00:09:09.519 with this thick, obscuring fog of neutral hydrogen. 195 00:09:09.159 --> 00:09:10.480 Gas, like a literal fog. 196 00:09:10.720 --> 00:09:15.240 Essentially, yeah, light could not travel freely. The cosmos was opaque. 197 00:09:15.360 --> 00:09:18.039 Astronomers call this period the Dark Ages. 198 00:09:18.159 --> 00:09:20.279 It was just a giant soup of hydrogen waiting for 199 00:09:20.320 --> 00:09:21.000 something to happen. 200 00:09:21.320 --> 00:09:25.440 Then the first stars and the first primitive galaxies ignited. 201 00:09:25.960 --> 00:09:30.960 And these early stars were monstrously massive, incredibly hot, and. 202 00:09:30.919 --> 00:09:33.799 They must have pumped out staggering amounts of radiation. 203 00:09:33.919 --> 00:09:38.559 Huge amounts of ultraviolet radiation. This intense UV radiation literally 204 00:09:38.639 --> 00:09:41.440 tore the electrons away from the neutral hydrogen atoms in 205 00:09:41.440 --> 00:09:42.320 the surrounding space. 206 00:09:42.399 --> 00:09:44.759 And that process is what we call reionization. 207 00:09:45.080 --> 00:09:48.360 Exactly, it burned away the fog, making the universe transparent. 208 00:09:48.720 --> 00:09:51.440 But this epoch was exceptionally violent. 209 00:09:51.639 --> 00:09:54.879 Violent. How like, if I'm this little forming bwarf galaxy 210 00:09:55.000 --> 00:09:57.720 gathering my own hydrogen to make my own stars, what 211 00:09:57.759 --> 00:09:59.519 does that uvwave actually do to me? 212 00:10:00.080 --> 00:10:03.039 A delicate system with a weak gravitational welt like in 213 00:10:03.200 --> 00:10:07.320 XX sixty six, that wave of intense radiation was absolutely. 214 00:10:06.799 --> 00:10:08.799 Devastating because it heated up the gas. 215 00:10:08.879 --> 00:10:11.600 Right. The intense UV light heated the gas inside these 216 00:10:11.639 --> 00:10:14.759 small dark matter halos, And when a gas heats up, 217 00:10:14.879 --> 00:10:16.120 its particles move faster. 218 00:10:16.440 --> 00:10:18.840 Oh I see, So the thermal kinetic energy of the 219 00:10:18.879 --> 00:10:22.879 gas rapidly exceeded the escape velocity of the tiny galaxies gravity. 220 00:10:23.000 --> 00:10:27.200 Exactly, the gas expanded and literally boiled away into deep space. 221 00:10:27.320 --> 00:10:30.279 It just got blasted dry by the bigger galaxies turning 222 00:10:30.320 --> 00:10:34.120 their lights on. And without cold dense gas, a galaxy 223 00:10:34.159 --> 00:10:35.720 cannot form new stars. 224 00:10:35.840 --> 00:10:39.519 The factory gets permanently shut down. The initial burst of 225 00:10:39.600 --> 00:10:42.639 star formation is abruptly quenched. Wow. 226 00:10:42.840 --> 00:10:45.120 And we can verify this quenching by looking at the 227 00:10:45.120 --> 00:10:46.639 galaxy's chemical signature, right. 228 00:10:46.720 --> 00:10:51.080 We can, specifically, we look at its metallicity. The spectroscopic 229 00:10:51.159 --> 00:10:54.960 data for XXS shows a metallicity of roughly negative two 230 00:10:55.039 --> 00:10:55.600 point five. 231 00:10:55.799 --> 00:10:58.519 I actually need to translate an astronomical quirk for everyone 232 00:10:58.559 --> 00:11:02.039 listening here, because metallicity in astronomy doesn't mean what it 233 00:11:02.080 --> 00:11:03.240 means in chemistry class. 234 00:11:03.279 --> 00:11:04.159 No, it definitely doesn't. 235 00:11:04.200 --> 00:11:07.120 To an astronomer, anything heavier than hydrogen and helium is 236 00:11:07.120 --> 00:11:11.200 considered a metal, like oxygen, carbon, nitrogen. Those are all 237 00:11:11.279 --> 00:11:12.559 metals in this context. 238 00:11:12.919 --> 00:11:15.919 It's a funny historical artifact in the terminology, but the 239 00:11:15.919 --> 00:11:19.000 physics it describes tells a vital story about the universe. 240 00:11:19.399 --> 00:11:23.399 Because the Big Bang essentially produced only hydrogen, helium, and 241 00:11:23.559 --> 00:11:26.159 a microscopic trace of lithium right right. 242 00:11:26.559 --> 00:11:30.639 All the heavier elements these astronomical metals were forged much later. 243 00:11:30.720 --> 00:11:34.240 They were crushed together inside the extreme heat and pressure. 244 00:11:33.919 --> 00:11:37.080 Of stellar cores, and then distributed across the universe when 245 00:11:37.080 --> 00:11:39.440 those stars died in supernova explosions. 246 00:11:39.679 --> 00:11:41.799 So the very first stars to ever exist in the 247 00:11:41.879 --> 00:11:44.759 universe were made of pure hydrogen and helium. They had 248 00:11:44.759 --> 00:11:46.559 a metallicity of basically zero. 249 00:11:46.840 --> 00:11:50.759 Correct. When those first generation stars exploded, they seeded the 250 00:11:50.799 --> 00:11:54.200 surrounding gas clouds with the newly forged heavier. 251 00:11:53.840 --> 00:11:56.960 Elements, So the second generation of stars formed from that 252 00:11:57.000 --> 00:12:00.519 slightly polluted gas, making their metallicity slightly higher. 253 00:12:00.759 --> 00:12:04.279 Exactly, the more generations of stars a galaxy produces, the 254 00:12:04.279 --> 00:12:06.080 more metal rich its gas becomes. 255 00:12:06.399 --> 00:12:08.919 I mean, our Sun is a relatively modern star, forming 256 00:12:08.960 --> 00:12:11.440 only about four point six billion years ago, so. 257 00:12:11.440 --> 00:12:14.120 It has a high metallicity because it formed from gas 258 00:12:14.240 --> 00:12:18.120 enriched by countless generations of dead stars over billions of years. 259 00:12:18.159 --> 00:12:21.200 An xpite has an incredibly low metallicity of negative two 260 00:12:21.200 --> 00:12:23.159 point five. It's chemically pristine. 261 00:12:23.240 --> 00:12:25.559 It barely has any heavy elements at all. It is 262 00:12:26.039 --> 00:12:31.159 absolute chemical conformation that there has been no recent star 263 00:12:31.279 --> 00:12:31.960 formation there. 264 00:12:32.039 --> 00:12:34.440 It is a completely unevolved system totally. 265 00:12:34.679 --> 00:12:37.879 It birthed its initial crop of stars roughly twelve point 266 00:12:37.919 --> 00:12:41.799 five billion years ago, the process of realization boiled away 267 00:12:41.840 --> 00:12:44.440 the rest of its fuel, and then it simply stopped. 268 00:12:44.519 --> 00:12:47.320 It's really like finding a perfectly preserved Roman ruin. 269 00:12:47.639 --> 00:12:48.639 That's a great analogy. 270 00:12:48.799 --> 00:12:52.480 Imagine uncovering a massive ancient city, but it was suddenly 271 00:12:52.559 --> 00:12:55.080 abandoned just a few decades after it was built, and 272 00:12:55.159 --> 00:12:57.480 nobody ever came back. It was never built over. 273 00:12:57.759 --> 00:13:00.080 You can see the original stones exactly as they. 274 00:13:00.639 --> 00:13:05.120 Right, whereas massive galaxies like our Milky Way or Andromeda 275 00:13:05.240 --> 00:13:08.759 are like modern, sprawling cities. They are built on top 276 00:13:08.759 --> 00:13:11.919 of countless layers of demolition and new construction. 277 00:13:11.600 --> 00:13:14.000 Paving over the old, mixing all the materials together. You 278 00:13:14.039 --> 00:13:16.759 can't easily see the ancient history because there's a skyscraper 279 00:13:16.799 --> 00:13:17.320 on top of it. 280 00:13:17.360 --> 00:13:20.000 But the undisturbed nature of X six sixty six is 281 00:13:20.000 --> 00:13:21.879 what makes it so incredibly valuable. 282 00:13:22.320 --> 00:13:26.000 Yes, because it lost its original gas, perhaps from that 283 00:13:26.120 --> 00:13:32.120 early universe reionization, or potentially due to brutal tidal interactions 284 00:13:32.120 --> 00:13:33.320 with Andromeda itself. 285 00:13:33.360 --> 00:13:37.639 Oh like Andromeda's immense gravity physically stripping the gas away 286 00:13:37.720 --> 00:13:39.480 as the dwarf galaxy orbits. 287 00:13:39.399 --> 00:13:42.600 Exactly Regardless of the exact mechanism of gas loss, its 288 00:13:42.639 --> 00:13:45.240 development was just frozen in time, and because. 289 00:13:45.039 --> 00:13:47.759 It lost its gas so early, it never formed enough 290 00:13:47.799 --> 00:13:51.320 stars to be bright, which brings us to the profound 291 00:13:51.480 --> 00:13:53.919 dimness and the story of how we actually found it, 292 00:13:54.000 --> 00:13:55.519 which is just ridiculous. 293 00:13:55.559 --> 00:13:56.639 It's an amazing story. 294 00:13:56.759 --> 00:14:00.840 We have this phenomenally dim, incredibly tiny, twelve point five 295 00:14:00.960 --> 00:14:04.399 billion year old ghost floating in the massive glare of Andromeda, 296 00:14:04.440 --> 00:14:06.919 barely emitting any light at all. How do you even 297 00:14:06.919 --> 00:14:07.399 find that? 298 00:14:07.440 --> 00:14:11.919 The discovery process highlights this fascinating intersection between massive astronomical 299 00:14:11.960 --> 00:14:14.320 survey data and pure human intuition. 300 00:14:14.559 --> 00:14:16.320 So where did the initial data come from? 301 00:14:16.399 --> 00:14:20.360 The foundational data came from the Panandromeda Archaeological Survey or PANDAAS. 302 00:14:20.639 --> 00:14:24.960 This was a sweeping deep imaging campaign utilizing the Canada, France, 303 00:14:25.000 --> 00:14:26.679 Hawaii telescope right. 304 00:14:26.559 --> 00:14:29.360 And the goal there was to map the extended halo 305 00:14:29.399 --> 00:14:32.960 of Andromeda, essentially looking deep into the galactic suburbs. 306 00:14:33.279 --> 00:14:37.960 Deep imaging surveys like pandas operate by taking incredibly long 307 00:14:38.080 --> 00:14:41.960 exposure photographs of the exact same patches of sky, just 308 00:14:42.000 --> 00:14:44.960 staring at the dark yes, and then stacking those images 309 00:14:45.000 --> 00:14:48.919 to capture the absolute faintest possible photons they generate an 310 00:14:48.960 --> 00:14:50.960 incomprehensible amount of data. 311 00:14:50.720 --> 00:14:54.440 Terabytes and terabytes of wide field images capturing millions of 312 00:14:54.480 --> 00:14:58.360 faint points of light. It's a digital Haystag of cosmic proportions. 313 00:14:58.399 --> 00:15:00.759 And this is where the story gets w wonderfully human 314 00:15:01.159 --> 00:15:04.279 because the person who found this wasn't an algorithm, and 315 00:15:04.320 --> 00:15:07.080 it wasn't a team of postdocs in a supercomputing lab. 316 00:15:07.159 --> 00:15:09.879 It was an amateur astronomer, right, Giuseppe Donaciello. 317 00:15:10.080 --> 00:15:14.159 Yes, despite all our advanced technology, Donaicello found this galaxy 318 00:15:14.200 --> 00:15:17.480 through systematic visual inspection of the PANDAS footprint. 319 00:15:17.639 --> 00:15:20.639 He literally just sat there, looked closely at the images 320 00:15:21.000 --> 00:15:24.200 and spotted an incredibly subtle overdensity of stars. 321 00:15:24.679 --> 00:15:28.639 Donnacila has a famously keen eye for spotting these structures. Actually, 322 00:15:28.960 --> 00:15:32.639 he has contributed to several previous Dwarf galaxy discoveries. 323 00:15:32.320 --> 00:15:35.360 Out in the outskirts of Andromeda and other nearby groups. 324 00:15:35.440 --> 00:15:39.840 Right, yeah, he possesses this unique visual acuity for identifying faint, 325 00:15:40.039 --> 00:15:44.639 diffuse stellar associations that just blend into the background for 326 00:15:45.200 --> 00:15:45.919 anyone else. 327 00:15:46.159 --> 00:15:50.159 But of course science requires verification and amateur spotting. A 328 00:15:50.240 --> 00:15:52.960 smudge on a monitor is the spark, but the professionals 329 00:15:53.000 --> 00:15:55.679 have to move in to prove it's actually a galaxy definitely. 330 00:15:55.759 --> 00:15:59.200 The professional follow up was spearheaded by Joanna di Sakowska 331 00:15:59.399 --> 00:16:02.279 from the Insane of Astrophysics of Andalusia. 332 00:16:01.879 --> 00:16:04.399 And they need an immense light gathering power to prove 333 00:16:04.440 --> 00:16:07.559 this wasn't an optical artifact or just a random clustering 334 00:16:07.600 --> 00:16:09.200 of four ground Milky Way stars. 335 00:16:09.360 --> 00:16:12.600 So they utilized the Osiris Plus instrument, which is mounted 336 00:16:12.639 --> 00:16:15.120 on the Grand Telescope you of Canarius in La Palma. 337 00:16:15.279 --> 00:16:18.759 That's a ten point four meter telescope that is serious 338 00:16:18.879 --> 00:16:19.759 heavy artillery. 339 00:16:19.919 --> 00:16:22.840 It is one of the premiere optical and infrared telescopes 340 00:16:22.879 --> 00:16:26.759 on the planet. Its massive mirror was absolutely necessary to 341 00:16:26.799 --> 00:16:29.799 capture enough light to resolve the individual stars within this 342 00:16:29.960 --> 00:16:31.320 faint smudge. 343 00:16:30.840 --> 00:16:33.399 So they aren't just looking at a blurry blob anymore. 344 00:16:33.480 --> 00:16:37.879 They are separating the blob into its constituent individual suns. 345 00:16:37.960 --> 00:16:41.799 Exactly, and by doing so they constructed a color magnitude 346 00:16:41.840 --> 00:16:43.639 diagram or CMD. 347 00:16:44.159 --> 00:16:46.080 I really want to break down what a color magnitude 348 00:16:46.120 --> 00:16:48.879 diagram actually is because this sounds intimidating, but it is 349 00:16:49.240 --> 00:16:51.679 one of the coolest diagnostic tools in. 350 00:16:51.639 --> 00:16:54.559 Astronomy, it's foundational to our understanding of stars. 351 00:16:54.720 --> 00:16:58.320 Imagine taking every individual star that the ten point four 352 00:16:58.399 --> 00:17:01.399 meter telescope resolved in that small ud and plotting it 353 00:17:01.440 --> 00:17:05.079 on a graph. The vertical axis is its magnitude, or 354 00:17:05.079 --> 00:17:05.839 how bright it. 355 00:17:05.759 --> 00:17:08.640 Is, and the horizontal axis is its color, which tells 356 00:17:08.640 --> 00:17:09.400 you its temperature. 357 00:17:09.599 --> 00:17:12.960 Right, Blue stars are brutally hot, red stars are cooler, and. 358 00:17:12.960 --> 00:17:16.359 Stars do not scatter randomly on this graph. Because the 359 00:17:16.480 --> 00:17:20.079 laws of stellar physics govern exactly how stars burn hydrogen, 360 00:17:20.440 --> 00:17:22.319 a group of stars born at the same time will 361 00:17:22.319 --> 00:17:25.960 align along very specific predictable curves. 362 00:17:25.680 --> 00:17:27.640 Right because they all form from the same cloud of 363 00:17:27.680 --> 00:17:28.839 gas exactly. 364 00:17:29.160 --> 00:17:32.480 The most massive blue hot stars burn through their fuel 365 00:17:32.480 --> 00:17:34.480 incredibly fast and die young. 366 00:17:34.799 --> 00:17:37.720 Will the smaller, cooler red stars burn their fuel slowly 367 00:17:37.799 --> 00:17:39.480 over hundreds of billions of years. 368 00:17:39.720 --> 00:17:42.640 So by looking at which stars are still burning and 369 00:17:42.720 --> 00:17:45.759 which are missing from that curve, you can tell exactly 370 00:17:45.799 --> 00:17:47.039 how old the whole group is. 371 00:17:47.240 --> 00:17:49.359 That is such a brilliant mechanism. 372 00:17:49.440 --> 00:17:52.480 It is by plotting the resolve stars from the Grand 373 00:17:52.480 --> 00:17:57.160 Telescopio Canarias, the team identified the unmistakable shape of an 374 00:17:57.200 --> 00:17:59.880 ancient metal poor stellar population. 375 00:18:00.200 --> 00:18:02.640 They found the main sequence turnoff point. 376 00:18:02.559 --> 00:18:06.200 Yes, the exact spot on the graph where stars of 377 00:18:06.240 --> 00:18:09.960 a certain mass are currently exhausting their hydrogen cores. 378 00:18:09.759 --> 00:18:12.559 And that turnoff point acts like a cosmic clock, providing 379 00:18:12.599 --> 00:18:15.240 that twelve point five billion year age estimate we talked 380 00:18:15.240 --> 00:18:16.160 about exactly. 381 00:18:16.559 --> 00:18:19.920 The stacked images also revealed a clear over density of 382 00:18:19.960 --> 00:18:24.519 these specific ancient stars, perfectly nestled between two incredibly bright 383 00:18:24.599 --> 00:18:25.559 four ground stars. 384 00:18:25.680 --> 00:18:28.279 Oh, those four grand stars are in our own Milky Way, 385 00:18:28.400 --> 00:18:31.359 right physically in the way, just photo bombing the image 386 00:18:31.400 --> 00:18:32.759 of the distant dwarf galaxy. 387 00:18:32.839 --> 00:18:35.599 They really are, But the data is definitive. This was 388 00:18:35.640 --> 00:18:37.279 a distinct galactic structure. 389 00:18:37.319 --> 00:18:39.920 But wait, let's be real here. It is twenty twenty six. 390 00:18:40.079 --> 00:18:42.480 We live in an era of massive computing power and 391 00:18:42.599 --> 00:18:45.599 highly advanced machine learning. We do Why on earth are 392 00:18:45.599 --> 00:18:47.960 we relying on a guy looking at a computer monitor 393 00:18:48.000 --> 00:18:51.880 to find this. Shouldn't a train algorithm have flagged this 394 00:18:52.000 --> 00:18:55.960 instant anomaly the millisecond the PANDEES data was uploaded. 395 00:18:56.079 --> 00:18:59.240 You'd think so, But the limits of our automated detection 396 00:18:59.359 --> 00:19:03.400 systems are really exposed in these extreme low surface brightness regimes. 397 00:19:03.559 --> 00:19:07.200 How so well machine learning algorithms are phenomenally powerful at 398 00:19:07.240 --> 00:19:10.519 recognizing patterns they have been explicitly trained to detect, and 399 00:19:10.559 --> 00:19:12.920 they are ruthlessly efficient at filtering out noise. 400 00:19:13.400 --> 00:19:17.359 But an ultra faint dwarf galaxy like an XXS operates 401 00:19:17.440 --> 00:19:19.799