WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.920 --> 00:00:29.440 You know, when you think about uncovering the past on Earth, 8 00:00:30.640 --> 00:00:34.280 whether you are looking at like a core sample of 9 00:00:34.280 --> 00:00:38.320 glacial ice or the rings of an ancient bristle comb pine, 10 00:00:38.799 --> 00:00:43.079 there is this fundamental expectation of structural layering. Time basically 11 00:00:43.200 --> 00:00:46.399 leaves a physical tactile mark. You dig down past the 12 00:00:46.439 --> 00:00:49.079 top soil, you hit a layer of limestone from the 13 00:00:49.159 --> 00:00:53.320 Jurassic period, and you have this, well, you have a 14 00:00:53.479 --> 00:00:57.960 chronological anchor. Time is buried in a specific measurable order. 15 00:00:58.119 --> 00:01:01.920 Yeah, exactly. The Earth act as a physical ledger. We 16 00:01:01.960 --> 00:01:05.000 rely really heavily on that spatial representation of time because 17 00:01:05.079 --> 00:01:08.480 you know, it grounds our understanding of history. We intuitively 18 00:01:08.519 --> 00:01:12.200 grasp that deeper usually means older, and we can test 19 00:01:12.239 --> 00:01:15.120 the material at each stratum to build a reliable timeline 20 00:01:15.159 --> 00:01:16.359 of planetary evolution. 21 00:01:16.640 --> 00:01:18.359 But the moment that you point a telescope at the 22 00:01:18.439 --> 00:01:22.439 night sky, that comforting geological layer cake just well, it 23 00:01:22.480 --> 00:01:25.040 completely vanishes, it really does. We're suddenly looking at a 24 00:01:25.079 --> 00:01:27.480 cosmic landscape that is, to the naked eye, and even 25 00:01:27.519 --> 00:01:31.200 to our most powerful traditional instruments, completely temporally flat. 26 00:01:31.280 --> 00:01:32.480 Right, it's completely flattened out. 27 00:01:32.640 --> 00:01:35.439 You look up and everything appears to be happening right now, 28 00:01:35.680 --> 00:01:38.879 all at once projected onto the inside of a sphere. 29 00:01:39.000 --> 00:01:42.959 It is the ultimate temporal illusion. Really, when we observe 30 00:01:43.079 --> 00:01:46.920 a starfield, we are bombarded by photons that left their 31 00:01:46.959 --> 00:01:50.519 sources at wildly different times. Yeah, I mean, we might 32 00:01:50.560 --> 00:01:53.040 see a star that just ignited a million years ago 33 00:01:53.159 --> 00:01:55.680 right next to a dying red giant that has been 34 00:01:55.719 --> 00:02:00.519 burning for ten billion years, and to us they are 35 00:02:00.560 --> 00:02:05.079 just two adjacent pinpricks of light on a flattened canvas, right. 36 00:02:05.120 --> 00:02:07.439 Because we lack that physical z axis of. 37 00:02:07.400 --> 00:02:09.919 Time exactly, we don't have depth when it comes to 38 00:02:10.000 --> 00:02:11.039 time in the sky. 39 00:02:11.159 --> 00:02:14.840 Which means in astronomy, the absolute hardest thing to figure 40 00:02:14.879 --> 00:02:17.000 out isn't what an object is, but when it is. 41 00:02:17.159 --> 00:02:20.840 Yes, age is the ultimate hidden variable in space and. 42 00:02:20.840 --> 00:02:24.560 Without knowing the age of a celestial object. You were 43 00:02:24.639 --> 00:02:27.319 essentially looking at a photograph of a stranger and trying 44 00:02:27.319 --> 00:02:29.960 to deduce their entire life story, right way to put it, 45 00:02:30.039 --> 00:02:33.680 like their internal biology, their future. Just from a single snapshot. 46 00:02:33.919 --> 00:02:36.680 You don't know the internal processes that are currently dominating 47 00:02:36.680 --> 00:02:37.360 their existence. 48 00:02:37.800 --> 00:02:42.800 Because age dictates nearly every physical characteristic of a celestial body. 49 00:02:43.319 --> 00:02:47.759 It dictates the internal structure, the temperature, the atmosphere, chemistry, 50 00:02:47.800 --> 00:02:50.199 and the evolutionary trajectory. 51 00:02:50.280 --> 00:02:50.879 Wow. 52 00:02:50.919 --> 00:02:54.879 Without an age, you cannot accurately model the physics of 53 00:02:54.919 --> 00:02:58.000 what you are actually looking at. You are simply cataloging 54 00:02:58.080 --> 00:03:02.879 static properties without understanding the dynamic timeline that produces them. 55 00:03:03.120 --> 00:03:07.199 So today we are going to explore a massive recent 56 00:03:07.319 --> 00:03:12.680 breakthrough where astrophysicists finally managed to crack this cosmic clock. 57 00:03:12.800 --> 00:03:15.599 And it's an incredible breakthrough, it really is, and they 58 00:03:15.639 --> 00:03:17.879 managed to do it on one of the most highly elusive, 59 00:03:18.400 --> 00:03:21.840 incredibly frustrating types of celestial objects in the universe. 60 00:03:21.919 --> 00:03:23.280 Oh, absolutely frustrating. 61 00:03:23.400 --> 00:03:26.800 We're going to explore the strange boundary between stars and planets, 62 00:03:27.120 --> 00:03:30.879 will learn how the physics of acoustic resonance literally starquakes 63 00:03:30.960 --> 00:03:32.840 solved a multi decade mystery. 64 00:03:32.560 --> 00:03:34.560 Which sounds like science fiction, but it's real. 65 00:03:34.599 --> 00:03:37.960 Right, and we will discover how one single finding is 66 00:03:38.080 --> 00:03:42.280 rewriting our understanding of cosmic time and evolution. Okay, let's 67 00:03:42.319 --> 00:03:46.199 unpack this sound, starting with the troublemakers themselves, the boundary 68 00:03:46.280 --> 00:03:49.240 dwellers brown dwarfs. 69 00:03:49.039 --> 00:03:55.039 Ah, brown dwarfs. They occupy a highly ambiguous mass range. 70 00:03:55.080 --> 00:03:58.639 They exist in this transitional void between the heaviest gas 71 00:03:58.680 --> 00:04:01.360 giant planets and the light main sequence. 72 00:04:00.960 --> 00:04:03.879 Stars, so they're stuck in the middle exactly. 73 00:04:04.199 --> 00:04:07.280 Generally, we classify them as objects with a mass between 74 00:04:07.520 --> 00:04:10.800 roughly thirteen and eighty times the mass of Jupiter. 75 00:04:10.960 --> 00:04:13.599 Okay, So, as you know, for a celestial body to 76 00:04:13.639 --> 00:04:17.839 become a true star, it has to achieve hydrostatic equilibrium. Right. 77 00:04:17.879 --> 00:04:20.759 You have a collapsing cloud of molecular gas. Gravity is 78 00:04:20.800 --> 00:04:24.160 crushing that mass inward, and the core pressure and temperature 79 00:04:24.240 --> 00:04:24.959 just skyrock. 80 00:04:25.040 --> 00:04:26.519 Yeah, it gets incredibly hot. 81 00:04:26.759 --> 00:04:29.720 And if that object has enough mass, specifically, if it 82 00:04:29.759 --> 00:04:33.399 crosses that threshold of about eighty Jupiter masses, the core 83 00:04:33.439 --> 00:04:37.600 temperature reaches millions of degrees and sustained hydrogen one fusion ignites. 84 00:04:37.720 --> 00:04:41.160 And that is the key that outward radiation pressure perfectly 85 00:04:41.240 --> 00:04:42.839 balances the inward pull of gravity. 86 00:04:42.920 --> 00:04:44.199 Right, they balance out that. 87 00:04:44.279 --> 00:04:48.240 Sustained hydrogen fusion is the defining characteristic of a main 88 00:04:48.319 --> 00:04:53.439 sequence star. It provides a constant, massive internal heat source 89 00:04:53.839 --> 00:04:57.519 that allows the star to shine steadily for billions of years. 90 00:04:57.879 --> 00:05:00.759 But a brown dwarf simply fails to reach that critical 91 00:05:00.759 --> 00:05:01.439 mass threshold. 92 00:05:01.519 --> 00:05:04.120 Right, Yeah, it just misses the mark. It forms from 93 00:05:04.160 --> 00:05:08.199 the same collapsing molecular clouds as stars do. It gathers mass, 94 00:05:08.439 --> 00:05:11.600 and its core heats up significantly under the crushing weight 95 00:05:11.639 --> 00:05:13.120 of its own gravity. 96 00:05:12.839 --> 00:05:14.480 Because there's still a lot of mass there. 97 00:05:14.399 --> 00:05:17.000 A lot of mass. Yeah. But before the core can 98 00:05:17.040 --> 00:05:20.240 get hot enough and dense enough to ignite stable hydrogen fusion, 99 00:05:20.399 --> 00:05:22.680 the collapse is halted by quantum mechanics. 100 00:05:22.720 --> 00:05:26.600 Wait, halted by quantum mechanics, You mean electron degeneracy pressure exactly. 101 00:05:26.959 --> 00:05:29.480 The electrons and the core get packed so tightly together 102 00:05:29.519 --> 00:05:31.480 that the poly exclusion principle kicks in. 103 00:05:31.680 --> 00:05:34.319 Right, They refuse to occupy the same quantum state, yes. 104 00:05:34.319 --> 00:05:38.000 Which creates an outward physical pressure that completely halts any 105 00:05:38.040 --> 00:05:39.480 further gravitational collapse. 106 00:05:39.560 --> 00:05:41.160 So the core becomes degenerate. 107 00:05:41.439 --> 00:05:44.040 It does, it locks the brown dwarf into a state 108 00:05:44.079 --> 00:05:46.800 where it can never achieve the core conditions required for 109 00:05:46.959 --> 00:05:48.519 main sequence hydrogen fusion. 110 00:05:48.879 --> 00:05:50.759 That's fascinating. So it's just stuck. 111 00:05:51.399 --> 00:05:53.879 Yeah, I mean some of the more massive brown dwarfs 112 00:05:53.959 --> 00:05:58.160 might briefly fuse deuterium, which is a heavier isotope of hydrogen, 113 00:05:58.920 --> 00:06:03.680 or even lithium. Okay, but those fuel sources are incredibly sparse, 114 00:06:03.800 --> 00:06:07.439 and they burn out very quickly in astronomical. 115 00:06:06.800 --> 00:06:08.120 Terms, like a flash in the pan. 116 00:06:08.399 --> 00:06:12.199 Precisely once that initial burst is over, the brown dwarf 117 00:06:12.319 --> 00:06:13.519 never truly turns on. 118 00:06:13.800 --> 00:06:16.759 It's essentially a cosmic engine that flooded before it could 119 00:06:16.800 --> 00:06:17.240 turn over. 120 00:06:17.519 --> 00:06:19.040 That is a perfect analogy. 121 00:06:19.199 --> 00:06:22.040 So because they lack that internal nuclear furnace to maintain 122 00:06:22.079 --> 00:06:26.279 this steady temperature, they spend their entire existence slowly fading 123 00:06:26.879 --> 00:06:29.800 like they are born hot from the primordial energy of 124 00:06:29.839 --> 00:06:34.279 their gravitational collapse, and then they spend billions of years 125 00:06:34.319 --> 00:06:36.959 just radiating that heat away into the vacuum space. 126 00:06:37.040 --> 00:06:40.800 Yeah, they just get colder and darker forever. 127 00:06:40.560 --> 00:06:42.160 Which sounds incredibly depressing. 128 00:06:42.279 --> 00:06:45.360 It's a lonely existence, but from a scientific standpoint, that 129 00:06:45.399 --> 00:06:49.000 continuous cooling curve is precisely what creates the massive headache 130 00:06:49.040 --> 00:06:50.879 for astrophysicists trying to study them. 131 00:06:51.079 --> 00:06:51.680 Why is that? 132 00:06:51.959 --> 00:06:55.279 Well, with a main sequence star like oursun the sustained 133 00:06:55.360 --> 00:06:59.680 fusion keeps the stars luminosity and temperature relatively stable for 134 00:07:00.160 --> 00:07:03.439 billions of years. We can plot it on a diagram 135 00:07:03.439 --> 00:07:04.720 and understand its life cycle. 136 00:07:04.839 --> 00:07:05.600 Oh, I see, But. 137 00:07:05.639 --> 00:07:09.319 A brown dwarf is constantly changing because its temperature and 138 00:07:09.399 --> 00:07:12.879 luminosity are always dropping. You cannot simply look at its 139 00:07:12.920 --> 00:07:16.680 current thermal emission and instantly know its evolutionary state. 140 00:07:16.879 --> 00:07:19.360 Wait, let me push back on that logic for a second. Sure, 141 00:07:19.519 --> 00:07:22.519 if a brown dwarf is literally just radiating its initial 142 00:07:22.560 --> 00:07:26.519 heat over time, we have incredibly sensitive thermal cameras, right 143 00:07:26.639 --> 00:07:30.439 we do. We use infrared observatories like JWST to measure 144 00:07:30.480 --> 00:07:34.680 thermal signatures across the galaxy all the time. Can't we 145 00:07:34.800 --> 00:07:37.879 just measure the exact infrared heat signature of the brown dwarf, 146 00:07:38.480 --> 00:07:41.879 calculate its physical volume, and backtrack the thermo dynamics to 147 00:07:41.920 --> 00:07:42.399 minute one? 148 00:07:42.639 --> 00:07:44.959 It seems like we should be able to Yeah, Like. 149 00:07:44.879 --> 00:07:47.600 Why can't we just take its temperature and derive the age? 150 00:07:47.720 --> 00:07:50.439 You could calculate the H that way, provided every single 151 00:07:50.480 --> 00:07:53.399 brown dwarf started its life with the exact same initial 152 00:07:53.439 --> 00:07:56.759 mass and the exact same reservoir of thermal energy. 153 00:07:56.680 --> 00:07:58.279 H And I'm guessing they don't. 154 00:07:58.480 --> 00:08:01.439 They absolutely don't. And this is where that electron degeneracy 155 00:08:01.480 --> 00:08:06.439 pressure creates an observational nightmare. How So, because a brown 156 00:08:06.519 --> 00:08:10.560 dwarf is supported by quantum degeneracy rather than thermal expansion, 157 00:08:10.959 --> 00:08:14.439 its physical radius is largely independent of its mass. 158 00:08:14.519 --> 00:08:16.800 Wait wait, wait, are you saying a lightweight brown dwarf 159 00:08:16.839 --> 00:08:20.040 and a massive brown dwarf or the exact same size. 160 00:08:19.800 --> 00:08:21.560 Roughly the same physical volume. 161 00:08:21.639 --> 00:08:23.160 Yes, that is wild. 162 00:08:23.480 --> 00:08:26.720 It really is counterintuitive. A brown dwarf at fifteen Jupiter 163 00:08:26.759 --> 00:08:29.800 masses has approximately the same radius as a brown dwarf 164 00:08:29.839 --> 00:08:31.639 at seventy five jupiter. 165 00:08:31.279 --> 00:08:33.360 Masses, So if I'm looking at it through a telescope, 166 00:08:33.399 --> 00:08:35.000 I can't tell the difference just based. 167 00:08:34.720 --> 00:08:38.559 On size exactly. So imagine you observe a brown dwarf 168 00:08:38.600 --> 00:08:42.240 with a measured surface temperature of five hundred kelvin. Because 169 00:08:42.240 --> 00:08:45.080 you can't determine its mass just by looking at its size, 170 00:08:45.480 --> 00:08:47.879 you are instantly faced with a paradox. 171 00:08:48.200 --> 00:08:51.120 I see the problem you just don't know the starting conditions, right. 172 00:08:51.519 --> 00:08:54.919 Is this a very lightweight fifteen jupiter mass brown dwarf 173 00:08:54.960 --> 00:08:59.200 that formed relatively recently, say, a few hundred million years ago, 174 00:08:59.360 --> 00:09:01.840 and hasn't had much time to cool down? Or is 175 00:09:01.919 --> 00:09:06.039 this a massive seventy jupiter mass brown dwarf that formed 176 00:09:06.240 --> 00:09:09.720 ten billion years ago, started with a massive reservoir of 177 00:09:09.759 --> 00:09:13.200 thermal energy and has been cooling down for an eternity 178 00:09:13.360 --> 00:09:16.080 to finally reach that same five hundred kelvin mark. 179 00:09:16.480 --> 00:09:19.000 Wow, So the low mass young object and the high 180 00:09:19.039 --> 00:09:23.000 mass ancient object look identical to our photometric instrument. 181 00:09:23.120 --> 00:09:26.080 You look exactly the same. That is a severe degeneracy problem. 182 00:09:26.120 --> 00:09:27.559 It's an absolute catch twenty two. 183 00:09:27.759 --> 00:09:28.360 It really is. 184 00:09:28.639 --> 00:09:32.080 To understand how a brown dwarf evolves. To map its 185 00:09:32.120 --> 00:09:35.840 specific cooling rate and figure out its mass, you absolutely 186 00:09:35.879 --> 00:09:39.279 need to know its precise age, yes, but to determine 187 00:09:39.320 --> 00:09:42.399 its exact age from its current temperature, you already need 188 00:09:42.440 --> 00:09:46.240 to know its mass and its specific evolutionary cooling track exactly. 189 00:09:46.279 --> 00:09:49.039 You need the age to solve the evolution, but you 190 00:09:49.080 --> 00:09:51.559 need the evolution to solve the age. It's an impossible 191 00:09:51.600 --> 00:09:52.279 loop that. 192 00:09:52.159 --> 00:09:54.240 Sounds incredibly frustrating. For astronomers. 193 00:09:54.440 --> 00:09:57.960 It is the defining frustration of substellar astrophysics. I mean, 194 00:09:58.039 --> 00:10:00.840 the object itself is locked in an ambiguit state, its 195 00:10:01.080 --> 00:10:04.639 luminosity and temperature are changing, its radius tells you nothing 196 00:10:04.639 --> 00:10:07.840 about its mass, and it simply refuses to provide any 197 00:10:07.879 --> 00:10:10.360 independent metric that reveals its age. 198 00:10:10.600 --> 00:10:11.480 So what did theorists do? 199 00:10:12.440 --> 00:10:17.360 Just guess Well, they spent decades building complex computational models 200 00:10:17.360 --> 00:10:21.000 predicting how these objects should cool based on various masses 201 00:10:21.080 --> 00:10:22.519 and atmospheric composition. 202 00:10:22.639 --> 00:10:23.919 But it couldn't prove it right. 203 00:10:24.000 --> 00:10:27.480 They had no way to definitively calibrate those models against reality. 204 00:10:27.720 --> 00:10:31.559 So because they couldn't interrogate the Brown dwarf directly, astronomers 205 00:10:31.559 --> 00:10:33.759 realized they had to find a loophole. They had to 206 00:10:33.799 --> 00:10:37.039 stop looking at isolated Brown dwarfs floating alone in the 207 00:10:37.039 --> 00:10:40.600 interstellar medium. They needed a twin. Yes, they needed a 208 00:10:40.600 --> 00:10:43.200 Brown dwarf gravitationally tethered to something that would give up 209 00:10:43.200 --> 00:10:46.360 its postestificate. And they found one of the constellation Pegasus 210 00:10:46.639 --> 00:10:49.000 in the Hr seven six to seventy two system. 211 00:10:48.759 --> 00:10:51.879 Ah yes Hr seven sixty seven two. It is a 212 00:10:51.919 --> 00:10:55.679 binary system located about fifty eight light years away. It 213 00:10:55.720 --> 00:10:59.279 consists of a primary solar type main sequence star and 214 00:10:59.360 --> 00:11:02.240 a faint sub stellar companion, the brown dwarf, yes, a 215 00:11:02.279 --> 00:11:05.399 brown dwarf in orbit around it, and this specific pairing 216 00:11:05.840 --> 00:11:08.480 is the key to breaking the entire catch twenty two 217 00:11:08.639 --> 00:11:10.519 of brown dwarf evolution. 218 00:11:10.320 --> 00:11:14.000 Because they coalesced from the exact same collapsing molecular cloud 219 00:11:14.039 --> 00:11:14.799 of gas and dust. 220 00:11:15.000 --> 00:11:18.559 Exactly, they share the same primordial origin. They formed at 221 00:11:18.559 --> 00:11:21.200 the exact same time from the same material, sharing the 222 00:11:21.240 --> 00:11:25.279 same initial metallicity. Right, even though one gathered enough mass 223 00:11:25.360 --> 00:11:28.240 to ignite hydrogen fusion and become a true star and 224 00:11:28.279 --> 00:11:30.960 the others stalled out as a brown dwarf, they are 225 00:11:31.039 --> 00:11:34.600 fundamentally siblings born in the same cosmic event. 226 00:11:34.559 --> 00:11:38.840 Which means therefore whatever age the primary main sequence star is, 227 00:11:39.080 --> 00:11:41.759 the brown dwarf companion must be the exact same age. 228 00:11:41.840 --> 00:11:43.159 That's the loophole, so the. 229 00:11:43.120 --> 00:11:46.279 Star becomes the proxy. If you could date the primary star, 230 00:11:46.720 --> 00:11:50.120 you immediately unlock the age of the brown dwarf. But wait, 231 00:11:50.240 --> 00:11:51.879 doesn't that just move the goalposts? 232 00:11:52.240 --> 00:11:52.600 Wow? 233 00:11:52.720 --> 00:11:55.600 Because means he can. Stars are famously difficult to date 234 00:11:55.639 --> 00:11:58.799 precisely once they settle into their mature phase. Right. Their 235 00:11:58.799 --> 00:12:02.759 surface temperatures and limit venosities don't change drastically for billions 236 00:12:02.799 --> 00:12:05.679 of years, So how did they force the primary star 237 00:12:05.840 --> 00:12:07.000 to reveal its age? 238 00:12:07.120 --> 00:12:10.000 This is where the methodology shifts from standard photometry to 239 00:12:10.200 --> 00:12:15.360 incredibly advanced high resolution spectroscopy. The researchers utilize the WM 240 00:12:15.480 --> 00:12:19.879 Keck Observatory in Hawaii. Specifically, they leveraged an instrument called 241 00:12:19.879 --> 00:12:22.799 the Kech planet Finder, and they didn't just measure the 242 00:12:22.840 --> 00:12:28.480 star's total light output. They employed astro seismology. Astroismology, yes, 243 00:12:28.519 --> 00:12:31.480 they study the internal acoustic waves of the star itself. 244 00:12:31.639 --> 00:12:34.039 What's fascinating here is that we tend to think of 245 00:12:34.039 --> 00:12:38.480 stars as these silent, static, glowing orbs. They do, but internally, 246 00:12:39.240 --> 00:12:42.879 a solar type star is a violently turbulent environment. 247 00:12:43.000 --> 00:12:43.639 It's chaotic. 248 00:12:43.799 --> 00:12:46.000 In the outer envelope of a star like Hr seven 249 00:12:46.120 --> 00:12:50.279 six seven to two, you have massive convection zones, huge 250 00:12:50.320 --> 00:12:53.720 plumes of superheated plasma are constantly boiling to the surface, 251 00:12:53.759 --> 00:12:57.759 cooling and sinking back down. And this violent, continuous churning 252 00:12:58.200 --> 00:13:00.000 generates broadband acoustic noise. 253 00:13:00.519 --> 00:13:03.480 It is an environment of unimaginable acoustic energy. I mean 254 00:13:03.519 --> 00:13:06.879 the turbulence in the convective envelope continuously excites millions of 255 00:13:06.879 --> 00:13:07.840 different sound waves. 256 00:13:07.879 --> 00:13:08.960 Sound waves in a star. 257 00:13:08.960 --> 00:13:12.320 Yeah, these are pressure waves or p modes. And because 258 00:13:12.440 --> 00:13:16.320 the star is a bounded sphere of dense plasma, it 259 00:13:16.399 --> 00:13:18.919 acts as a three dimensional resonant cavity. 260 00:13:19.159 --> 00:13:21.480 So the star literally rings like a bell. 261 00:13:21.759 --> 00:13:22.759 It literally does. 262 00:13:22.960 --> 00:13:25.840 The physics of this are just incredible. These acoustic waves 263 00:13:26.120 --> 00:13:29.879 travel downward from the surface into the dense interior of 264 00:13:29.919 --> 00:13:32.399 the star. Right, But the speed of sound in a 265 00:13:32.440 --> 00:13:36.440 plasma depends heavily on the temperature and the mean molecular 266 00:13:36.440 --> 00:13:37.320 weight of that plasma. 267 00:13:37.399 --> 00:13:39.159 Right, Yes, those are the key variable. 268 00:13:39.279 --> 00:13:41.559 So as the sound waves dive deeper toward the core, 269 00:13:42.000 --> 00:13:45.919 the temperature and density increase dramatically, which causes the sound 270 00:13:45.919 --> 00:13:50.000 waves to refract. They curve back upward towards the surface. 271 00:13:49.720 --> 00:13:52.360 And when those refracted sound waves hit the surface of 272 00:13:52.399 --> 00:13:55.320 the star from the inside, they cause the star's outer 273 00:13:55.440 --> 00:14:00.879 layers to physically expand and contract. Wow, the entire starstantly pulsating, 274 00:14:00.960 --> 00:14:04.559 driven by this internal acoustic resonance. But the crucial part 275 00:14:04.600 --> 00:14:07.600 of astro seismology, the mechanism that actually allows us to 276 00:14:07.679 --> 00:14:11.080 date the star, lies in how that internal sound speed 277 00:14:11.440 --> 00:14:12.399 changes over time. 278 00:14:12.559 --> 00:14:15.080 Right, Because the core composition of the star is not static. 279 00:14:15.559 --> 00:14:19.759 As the star ages, it fuses hydrogen into helium. 280 00:14:19.399 --> 00:14:22.840 And helium is denser and heavier than hydrogen. Okay, So 281 00:14:22.879 --> 00:14:26.279 as the star burns through its main sequence life, helium 282 00:14:26.320 --> 00:14:28.360 ash slowly accumulates in the core. 283 00:14:28.960 --> 00:14:29.679 That makes sense. 284 00:14:29.840 --> 00:14:33.720 This gradually increases the mean molecular weight of the star's interior. 285 00:14:34.039 --> 00:14:37.039 And because the speed of sound is inversely proportional to 286 00:14:37.080 --> 00:14:39.759 the square root of the mean molecular weight, the build 287 00:14:39.840 --> 00:14:43.039 up of helium physically alters the sound speed profile of 288 00:14:43.080 --> 00:14:43.919 the entire star. 289 00:14:44.600 --> 00:14:47.879 I see. So, as the star ages, the internal acoustic 290 00:14:47.919 --> 00:14:51.440 cavity changes its properties, which means the specific frequencies at 291 00:14:51.440 --> 00:14:54.600 which the star resonates the pitch of the starquakes shifts 292 00:14:54.639 --> 00:14:55.159 over time. 293 00:14:55.279 --> 00:14:58.639 You've got it. By meticulously measuring the frequencies of those 294 00:14:58.679 --> 00:15:03.720 surface pulsations, astrophysicists can essentially perform an ultrasound on the star. 295 00:15:03.919 --> 00:15:07.120 An ultrasound on a star that is wild. 296 00:15:06.799 --> 00:15:10.039 It's amazing. They map the internal density profile, They determine 297 00:15:10.080 --> 00:15:12.600 exactly how much helium has accumulated in the core, and 298 00:15:12.639 --> 00:15:15.639 from that mass, fraction of helium ash. They can calculate 299 00:15:15.679 --> 00:15:18.000 the star's age with astonishing precision. 300 00:15:18.159 --> 00:15:20.320 But I mean, this scale of this measurement is what 301 00:15:20.399 --> 00:15:21.559 truly blows my mind. 302 00:15:21.720 --> 00:15:23.080 It's hard to wrap your head around. 303 00:15:23.240 --> 00:15:26.720 We are talking about acoustic waves causing a star to 304 00:15:26.799 --> 00:15:30.240 expand and contract by a few meters on an object 305 00:15:30.279 --> 00:15:33.879 that is millions of kilometers across, located fifty eight light 306 00:15:33.960 --> 00:15:37.679 years away. Yeah, how is an instrument on Earth measuring 307 00:15:37.720 --> 00:15:38.879 that physical pulsation? 308 00:15:39.039 --> 00:15:41.639 Well? As the surface of the star heaves out well 309 00:15:41.759 --> 00:15:45.440 toward Earth and then contracts inward away from Earth, the 310 00:15:45.559 --> 00:15:50.360 light emitted from that surface undergoes a microscopic Doppler shift. 311 00:15:50.600 --> 00:15:51.919 Ah, the Doppler effect. 312 00:15:52.000 --> 00:15:55.000 Right, when the surface moves toward us, the light waves 313 00:15:55.000 --> 00:15:58.720 are compressed, shifting slightly toward the blue end of the spectrum. Okay, 314 00:15:58.759 --> 00:16:01.759 and when it moves away, the light stretches, shifting toward 315 00:16:01.840 --> 00:16:02.200 the red. 316 00:16:02.399 --> 00:16:05.720 So the Keck planet finder isn't taking pictures. No, it's 317 00:16:05.759 --> 00:16:09.559 a high resolution a shell spectrograph breaking the starlight apart 318 00:16:09.639 --> 00:16:13.360 and looking for these minuscule rhythmic shifts in the absorption lines. 319 00:16:13.679 --> 00:16:17.360 And the precision required is just staggering. We are looking 320 00:16:17.360 --> 00:16:21.200 for radial velocity shifts on the order of centimeters per second. 321 00:16:21.240 --> 00:16:23.240 Centimeters per second, that's barely a walking pace. 322 00:16:23.440 --> 00:16:28.000 It's incredibly slow. The Keck planet finder uses advanced technology 323 00:16:28.240 --> 00:16:33.480 like laser frequency combs to create an absolute calibration grid. 324 00:16:33.600 --> 00:16:33.919 Okay. 325 00:16:34.159 --> 00:16:37.279 This ensures that any shift they measure is genuinely coming 326 00:16:37.320 --> 00:16:41.480 from the star and not from microscopic temperature fluctuations in 327 00:16:41.559 --> 00:16:45.000 the instrument itself. They are measuring variations in the starlight 328 00:16:45.080 --> 00:16:47.639 occurring on time scales of mere minutes. 329 00:16:47.960 --> 00:16:49.960 It's like trying to measure the ripples in a cup 330 00:16:50.000 --> 00:16:52.919 of coffee from a mile away by watching how the 331 00:16:52.960 --> 00:16:55.399 glare of the sun bounces off the surface of the 332 00:16:55.440 --> 00:16:58.799 liquid while staring through the turbulent atmosphere of the Earth. 333 00:16:58.879 --> 00:17:02.039 That is a very accurate, if slightly terrifying way to 334 00:17:02.039 --> 00:17:04.799 describe the engineering challenge. Yes, it's bordering on magic, but 335 00:17:04.839 --> 00:17:05.440 they did it. 336 00:17:05.559 --> 00:17:08.920 They isolated the acoustic modes of HR seven six seventy two, 337 00:17:09.400 --> 00:17:11.680 They mapped the helium density of the core, and they 338 00:17:11.720 --> 00:17:13.680 derived a precise independent age. 339 00:17:13.720 --> 00:17:16.279 They did the astra seismic data confirmed that the Hr 340 00:17:16.319 --> 00:17:18.799 seven sixty seven to two system is exactly two point 341 00:17:18.839 --> 00:17:20.240 three billion years old. 342 00:17:20.079 --> 00:17:23.240 Two point three billion years, which instantly assigns that exact 343 00:17:23.279 --> 00:17:25.039 same age to the brown dwarf companion. 344 00:17:25.759 --> 00:17:26.599 Mystery solved. 345 00:17:26.799 --> 00:17:30.480 They finally bypassed the degeneracy problem and forced a brown 346 00:17:30.559 --> 00:17:32.079 dwarf to hand over its birth certify. 347 00:17:32.200 --> 00:17:33.680 Yes, they finally got the timestamp. 348 00:17:34.039 --> 00:17:39.279 But I want to explore why the astrophysics community views 349 00:17:39.400 --> 00:17:42.720 this specific system as such a massive breakthrough. 350 00:17:42.839 --> 00:17:43.920 Okay, let's get into it. 351 00:17:43.880 --> 00:17:47.720 Because surely we have found other brown dwarfs orbiting stars before. 352 00:17:48.640 --> 00:17:50.359 Why does this one change the game. 353 00:17:51.000 --> 00:17:54.240 Well, while we have detected other brown dwarfs and binary systems, 354 00:17:54.279 --> 00:17:57.880 the specific orbital architecture of HR seventy six seven to 355 00:17:57.960 --> 00:18:01.640 two is exceedingly rare. Oh so, this brown dwarf is 356 00:18:01.799 --> 00:18:05.119 orbiting relatively close to its host star. Okay, when you 357 00:18:05.160 --> 00:18:09.759 analyze the statistical distribution of substellar companions orbiting solar type 358 00:18:09.799 --> 00:18:13.279 stars at these close to intermediate distances we're talking roughly 359 00:18:13.319 --> 00:18:18.039 within five astronomical units, you find a glaring statistical anomaly. 360 00:18:17.640 --> 00:18:18.519 Well kind of anomaly. 361 00:18:18.559 --> 00:18:20.759 Astrophysicists call it the Brown dwarf desert. 362 00:18:20.839 --> 00:18:23.720 A desert, a zone where these objects simply do not exist. 363 00:18:23.799 --> 00:18:26.960 We find terrestrial planets close to stars, we find gas 364 00:18:26.960 --> 00:18:30.640 giants like Jupiter slightly further out, but in that specific 365 00:18:30.759 --> 00:18:34.319 mass range of thirteen to eighty jupiter masses, the data 366 00:18:34.359 --> 00:18:35.720 suddenly drops off a cliff. 367 00:18:35.920 --> 00:18:38.640 It is a profound accents and it points to the 368 00:18:38.640 --> 00:18:42.839 fundamental mechanics of how different objects form in a protoplanetary disk. 369 00:18:42.920 --> 00:18:43.559 How do they form? 370 00:18:43.920 --> 00:18:47.960 Well? Planets form through core recretion. Dust grains stick together, 371 00:18:48.119 --> 00:18:51.920 form pebbles, then planetesimals, and eventually, if a rocky core 372 00:18:51.960 --> 00:18:55.720 gets massive enough, it rapidly sweeps up surrounding gas to 373 00:18:55.759 --> 00:18:59.319 become a giant planet like Jupiter. Right, But that process 374 00:18:59.359 --> 00:19:02.039 seems to hit a hard upper limit, well below the 375 00:19:02.079 --> 00:19:04.000 mass of a brown dwarf. 376 00:19:03.880 --> 00:19:05.920 Because by the time a core could accrete forty or 377 00:19:05.920 --> 00:19:09.400 fifty jupiter masses of gas, the primordial disc has either 378 00:19:09.440 --> 00:19:12.559 dissipated or the growing planet has carved such a massive 379 00:19:12.599 --> 00:19:15.680 gap in the disc that it starves itself a further material. 380 00:19:15.759 --> 00:19:18.559 Precisely, you just run out of raw material. Brown dwarfs, 381 00:19:18.559 --> 00:19:20.920 on the other hand, likely form through the same mechanism 382 00:19:20.920 --> 00:19:24.079 as stars, the racket gravitational fragmentation and collapse of a 383 00:19:24.119 --> 00:19:25.000 molecular cloud. 384 00:19:25.240 --> 00:19:26.359 So they form like stars. 385 00:19:26.799 --> 00:19:30.680 Yes, but forming a star and a brown dwarf simultaneously 386 00:19:31.200 --> 00:19:35.920 in such close proximity creates an incredibly unstable dynamic environment. 387 00:19:36.000 --> 00:19:36.920 Oh I could imagine. 388 00:19:36.960 --> 00:19:40.880 In most cases, the complex multibody gravitational interactions during the 389 00:19:40.880 --> 00:19:44.519 formation phase either eject the lighter brown dwarf out of 390 00:19:44.519 --> 00:19:48.200 the system entirely or force it to spiral inward and 391 00:19:48.319 --> 00:19:49.720 merge with the primary star. 392 00:19:49.920 --> 00:19:52.440 So the environment is just too violent for the brown 393 00:19:52.480 --> 00:19:55.119 dwarf to survive in that orbit. Yes, so finding the 394 00:19:55.319 --> 00:19:58.960 Hr seven six seven to two brown dwarf sitting perfectly 395 00:19:58.960 --> 00:20:01.720 intact right in the middle of this desert is an 396 00:20:01.759 --> 00:20:02.799 extreme anomaly. 397 00:20:03.039 --> 00:20:07.200 It's incredibly lucky it survived the chaotic formation process, and. 398 00:20:07.079 --> 00:20:10.200 Its survival in that specific orbit is what makes it 399 00:20:10.319 --> 00:20:11.519 scientifically invaluable. 400 00:20:11.640 --> 00:20:15.799 Exactly when theorists attempt to test complex physics models like 401 00:20:15.839 --> 00:20:19.279