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 00:00:26.960 --> 00:00:30.800 Imagine taking one hundred and fifty earths. 8 00:00:31.039 --> 00:00:33.520 That is a staggering amount of material. 9 00:00:33.280 --> 00:00:36.920 Right, Just picture every single ocean, every mountain range, every 10 00:00:37.000 --> 00:00:40.640 sprawling continent, and you know, every molten iron core. 11 00:00:41.159 --> 00:00:44.719 Just an incomprehensible volume of solid rock and metal. 12 00:00:44.880 --> 00:00:47.240 Exactly Now, I want you to take all of that 13 00:00:47.359 --> 00:00:51.320 solid mass, grind it down into cosmic dust, and dissolve 14 00:00:51.320 --> 00:00:55.520 it entirely into the atmosphere of a single raging gas storm, a. 15 00:00:55.520 --> 00:00:59.159 Storm that is spinning something like one point five billion 16 00:00:59.240 --> 00:00:59.920 miles away from it. 17 00:01:00.600 --> 00:01:04.400 Yeah, one point five billion miles. By every established metric 18 00:01:04.439 --> 00:01:07.840 of planetary physics, an object like that shouldn't be mathematically possible. 19 00:01:07.959 --> 00:01:10.400 It really shouldn't. I mean, the mechanisms required to build 20 00:01:10.480 --> 00:01:13.519 something that massive that far out in the frozen reaches 21 00:01:13.519 --> 00:01:16.200 of a star system. They just don't fit into our 22 00:01:16.239 --> 00:01:17.400 standard model. 23 00:01:17.239 --> 00:01:19.400 Right, our models of how the universe is supposed to work. 24 00:01:20.000 --> 00:01:23.400 But today we are looking directly at a celestial behemoth 25 00:01:23.439 --> 00:01:24.400 that did exactly that. 26 00:01:24.519 --> 00:01:27.200 It's an object that basically forces us to question the 27 00:01:27.200 --> 00:01:29.719 fundamental dividing line between planets and stars. 28 00:01:29.760 --> 00:01:31.239 It totally blurs that line. 29 00:01:31.319 --> 00:01:34.840 It forces a complete reevaluation. Yeah, because well we find 30 00:01:34.840 --> 00:01:37.200 deep comfort in neat categorizations. 31 00:01:37.239 --> 00:01:40.599 Well, it's absolutely human nature, right. We love our little boxes. 32 00:01:40.239 --> 00:01:43.120 We really do. We prefer a universe where you have, 33 00:01:43.760 --> 00:01:46.359 you know, planets on one side, objects built from rock 34 00:01:46.359 --> 00:01:48.519 and ice that maybe sweep up some gas over. 35 00:01:48.400 --> 00:01:50.519 Time, and then stars on the other side. 36 00:01:50.200 --> 00:01:55.120 Exactly, stars being these massive self collapsing clouds of nuclear fire. 37 00:01:55.439 --> 00:01:57.959 We like a hard absolute boundary there. 38 00:01:58.040 --> 00:02:01.280 But when you actually examine the extreme edge of astrophysics, 39 00:02:02.120 --> 00:02:06.040 that boundary doesn't just blur. It kind of well, it 40 00:02:06.239 --> 00:02:07.799 completely dissolves. 41 00:02:07.439 --> 00:02:10.680 It does you find objects that possess the defining characteristics 42 00:02:10.680 --> 00:02:14.080 of both existing in this state of absolute diagnostic contradiction, 43 00:02:14.240 --> 00:02:14.639 and that. 44 00:02:14.560 --> 00:02:17.800 Brings us to the specific anomaly you asked us to investigate. Today, 45 00:02:18.080 --> 00:02:20.080 we're talking about twenty nine signey. 46 00:02:19.719 --> 00:02:21.840 B the ultimate cosmic gray area. 47 00:02:22.000 --> 00:02:24.360 Yeah, and just to anchor the scale here for you, 48 00:02:24.439 --> 00:02:27.400 twenty nine signy B is a gas giant with a 49 00:02:27.439 --> 00:02:30.319 mass roughly fifteen times that of Jupiter. 50 00:02:30.080 --> 00:02:32.199 Which is just a terrifying amount of mass. 51 00:02:31.919 --> 00:02:35.400 Fifteen jupiters mashed together into a single sphere, and it 52 00:02:35.439 --> 00:02:38.080 maintains an orbit at a staggering distance of one point 53 00:02:38.159 --> 00:02:39.199 five billion. 54 00:02:38.840 --> 00:02:42.479 Mile that's about two point four billion kilometers for anyone 55 00:02:42.520 --> 00:02:43.719 doing the conversion right. 56 00:02:44.159 --> 00:02:47.120 So if you drop this system into our own solar neighborhood, 57 00:02:47.719 --> 00:02:50.159 twenty nine signey B would be orbiting at almost the 58 00:02:50.240 --> 00:02:53.240 exact same distance Urinus is from our Sun. 59 00:02:53.360 --> 00:02:57.199 Which is precisely the detail that makes this such a profound. 60 00:02:56.840 --> 00:02:58.759 Mystery, because it's so far out in the dark. 61 00:02:58.919 --> 00:03:02.120 Exactly, you have a mass that borders on the stellar right, 62 00:03:02.479 --> 00:03:05.080 but combined with an orbital distance that sits in the 63 00:03:05.120 --> 00:03:07.520 deep frieze of a planetary system. 64 00:03:07.599 --> 00:03:10.039 What's basically having an identity crisis. 65 00:03:09.759 --> 00:03:12.280 A massive one. When you look at the mechanics of 66 00:03:12.360 --> 00:03:16.319 how celestial bodies are actually constructed. Twenty nine signy Bee 67 00:03:16.759 --> 00:03:20.960 challenges the timelines, the material availability, and just the fundamental 68 00:03:20.960 --> 00:03:22.840 physics of the whole construction process. 69 00:03:23.039 --> 00:03:25.560 So our mission for today is to figure out how 70 00:03:25.599 --> 00:03:28.280 astronomers unraveled that identity crisis. 71 00:03:28.400 --> 00:03:31.360 It's a fantastic piece of detective work, it really is. 72 00:03:32.120 --> 00:03:34.199 We need to look at how a team led by 73 00:03:34.240 --> 00:03:37.280 William Balmer at Johns Hopkins University and the Space Telescope 74 00:03:37.319 --> 00:03:41.080 Science Institute actually managed to prove something incredible. 75 00:03:40.680 --> 00:03:44.240 Right, that even the most massively incomprehensible gas giants can 76 00:03:44.240 --> 00:03:45.439 be built from the ground. 77 00:03:45.199 --> 00:03:48.800 Up, even the ones we traditionally suspected being like failed stars. 78 00:03:49.479 --> 00:03:51.280 But before we get to the detective work with the 79 00:03:51.360 --> 00:03:54.520 James Webb Telescope, we need to lay down some ground rules. 80 00:03:54.639 --> 00:03:56.360 We have to understand the baseline. 81 00:03:55.960 --> 00:03:59.439 Yet, right, we need to understand the two very distinct, 82 00:03:59.759 --> 00:04:03.759 fundamentally opposed ways the universe goes about building worlds. 83 00:04:04.319 --> 00:04:08.400 Because the universe essentially operates two completely different construction sites. 84 00:04:08.479 --> 00:04:10.719 Okay, let's look at the first one. This is the 85 00:04:10.759 --> 00:04:13.360 process that built the ground we are sitting on right now. 86 00:04:13.280 --> 00:04:16.399 Right, Yes, the bottom up process. It's traditionally known as 87 00:04:16.439 --> 00:04:21.480 core accretion. This is the classic standard mechanism for planet formation. 88 00:04:21.759 --> 00:04:24.240 Okay, let's break down accretion because it sounds simple on 89 00:04:24.279 --> 00:04:27.920 the surface, you know, just stuff bumping into other stuff. 90 00:04:27.720 --> 00:04:28.720 Like rolling a snowball. 91 00:04:28.920 --> 00:04:31.800 Right, but the physical reality of doing that on a 92 00:04:31.839 --> 00:04:34.759 cosmic scale has to be intensely complicated. 93 00:04:34.839 --> 00:04:37.759 Oh, it is incredibly complex. Yeah, and it operates under 94 00:04:37.800 --> 00:04:39.920 a strict, unforgiving time limit. 95 00:04:40.199 --> 00:04:41.560 Wait, a time limit? Why? 96 00:04:41.839 --> 00:04:42.160 Well? 97 00:04:42.360 --> 00:04:46.959 Core accretion begins inside a protoplanetary disk. When a newborn 98 00:04:47.000 --> 00:04:50.199 star ignites. It doesn't consume all the material in its 99 00:04:50.199 --> 00:04:54.399 stellar nursery, so there's leftovers exactly. The star is surrounded 100 00:04:54.439 --> 00:04:59.240 by this vast, flattened, spinning disc of leftover hydrogen, helium 101 00:04:59.680 --> 00:05:03.279 and a tiny, tiny fraction of microscopic dust grains. 102 00:05:03.839 --> 00:05:05.399 How microscopic are we talking? 103 00:05:05.519 --> 00:05:09.519 Unimaginably small, often just fractions of a micron across. They're 104 00:05:09.519 --> 00:05:11.879 mostly composed of silicates, carbon, and ice. 105 00:05:12.199 --> 00:05:14.079 So the star is sitting in the center of this 106 00:05:14.160 --> 00:05:18.639 spinning cosmic soup. But how do those microscopic grains ever 107 00:05:18.720 --> 00:05:21.959 become something the size of Earth litt alone Jupiter. It 108 00:05:21.959 --> 00:05:24.519 takes a lot of steps, because gravity can't possibly be 109 00:05:24.560 --> 00:05:26.639 strong enough to pull microscopic dust together. 110 00:05:26.759 --> 00:05:29.879 Right, You're absolutely right, it isn't. In the very early stages, 111 00:05:29.920 --> 00:05:34.040 gravity is entirely irrelevant. The initial growth relies entirely on 112 00:05:34.160 --> 00:05:36.639 electrostatic forces and molecular. 113 00:05:36.160 --> 00:05:38.240 Bonds, so it's basically just chemistry at that point. 114 00:05:38.399 --> 00:05:41.839 It is quite literal chemistry. As these microscopic grains drift 115 00:05:41.879 --> 00:05:44.360 through the gas in the disc, they collide, and if 116 00:05:44.399 --> 00:05:47.399 the collision is gentle enough Vandrvhal's forces. 117 00:05:47.519 --> 00:05:50.360 Those are the slight electromagnetic attractions between. 118 00:05:50.199 --> 00:05:54.360 Molecules, right, yeah, exactly, Those forces allow them to step together. 119 00:05:54.720 --> 00:05:59.639 They form these incredibly fragile, fluffy aggregates. Think of like 120 00:05:59.839 --> 00:06:01.279 cosmic dust buddies. 121 00:06:01.360 --> 00:06:03.319 Okay, dust bunnies I can visualize. 122 00:06:03.319 --> 00:06:05.519 But as they grow to the size of sand grains 123 00:06:05.560 --> 00:06:09.319 and then pebbles, they face a gauntlet of physical challenges. 124 00:06:09.480 --> 00:06:12.720 Challenges like what I mean. I assume space is mostly empty, 125 00:06:12.759 --> 00:06:15.639 So shouldn't they just keep coasting and sticking together. 126 00:06:15.759 --> 00:06:18.560 You have to remember the disc is mostly gas, and 127 00:06:18.600 --> 00:06:20.879 that gas creates aerodynamic drag. 128 00:06:21.079 --> 00:06:22.480 Oh, so they're fighting a headwind. 129 00:06:22.639 --> 00:06:26.040 Exactly, as these pebbles grow larger, they begin to decouple 130 00:06:26.079 --> 00:06:30.040 from the gas flow, they experience a serious headwind. This 131 00:06:30.120 --> 00:06:33.879 headwind SAPs their orbital momentum, which causes them to slowly 132 00:06:33.959 --> 00:06:35.839 spiral inward toward the star. 133 00:06:35.800 --> 00:06:37.839 They're falling in. That seems like a bad design. 134 00:06:37.920 --> 00:06:40.600 It gets worse once objects reach about the size of 135 00:06:40.639 --> 00:06:44.279 a boulder roughly a meter across, the electrostatic forces are 136 00:06:44.319 --> 00:06:46.959 no longer sufficient to hold them together if they collide at. 137 00:06:46.959 --> 00:06:49.319 High speeds, so instead of sticking. 138 00:06:49.040 --> 00:06:52.040 They shatter. They smash each other back into dust. This 139 00:06:52.120 --> 00:06:55.399 is famously known in astrophysics as the meter size barrier. 140 00:06:55.800 --> 00:06:59.079 That sounds like a fundamental flaw in the planetary assembly line. 141 00:06:59.319 --> 00:07:02.480 If boulders just smash each other back into dust or 142 00:07:02.560 --> 00:07:05.240 spiral into the star because of gas drag, how does 143 00:07:05.279 --> 00:07:07.920 anything ever survive long enough to become a planet. 144 00:07:08.000 --> 00:07:11.319 That was a persistent headache for astrophysicists for decades. 145 00:07:11.360 --> 00:07:13.600 Actually, I can imagine. So what's the workaround? 146 00:07:13.920 --> 00:07:16.800 The current understanding involves areas of the disc where gas 147 00:07:16.800 --> 00:07:20.759 pressure is slightly higher, creating local traps like pressure pockets, yeah, 148 00:07:20.800 --> 00:07:25.120 pressure bumps. In these bumps, the gas headwind essentially disappears, 149 00:07:25.160 --> 00:07:28.600 allowing the pebbles and boulders to accumulate in massive dense 150 00:07:28.639 --> 00:07:32.680 swarms well also a cosmic traffic jam a perfect analogy. 151 00:07:32.920 --> 00:07:35.560 And when the density of these solid swarms reaches a 152 00:07:35.560 --> 00:07:40.279 critical threshold, their collective mutual gravity finally takes over. 153 00:07:40.439 --> 00:07:42.480 So gravity finally kicks in big time. 154 00:07:42.560 --> 00:07:46.600 The entire swarm collapses in on itself almost instantly, completely 155 00:07:46.639 --> 00:07:50.439 bypassing that meter sized barrier to form solid bodies that 156 00:07:50.519 --> 00:07:52.079 are hundreds of kilometers across. 157 00:07:52.120 --> 00:07:53.240 And those are the planetesimals. 158 00:07:53.319 --> 00:07:54.480 We call them planet tesimals. 159 00:07:54.519 --> 00:07:58.000 Yes, so chemistry gets you to pebbles, aerodynamics forces the 160 00:07:58.000 --> 00:08:01.759 pebbles into dense traffic jams, and then gravity suddenly forces 161 00:08:01.800 --> 00:08:04.519 the traffic jam to collapse into a solid rock that 162 00:08:04.639 --> 00:08:07.160 is the core in core accretion precisely. 163 00:08:07.480 --> 00:08:10.879 And once you have a planetesimal, gravity rules. It sweeps 164 00:08:10.879 --> 00:08:13.800 through the disc, using its gravitational cross section to pull 165 00:08:13.879 --> 00:08:16.879 in surrounding pebbles and other planetesimal. 166 00:08:16.240 --> 00:08:18.079 So it just bullies everything else in its path. 167 00:08:18.240 --> 00:08:21.759 It really does. It grows into a protoplanet. Now, if 168 00:08:21.800 --> 00:08:24.319 we are talking about building a rocky world like Earth, 169 00:08:24.399 --> 00:08:28.079 the process largely stops here. That takes tens of millions 170 00:08:28.160 --> 00:08:28.680 of years. 171 00:08:28.800 --> 00:08:30.639 Okay, but what if we want to build a Jupiter. 172 00:08:30.839 --> 00:08:33.279 If we are building a gas giant, the protoplanet must 173 00:08:33.320 --> 00:08:36.679 reach a critical mass to typically around ten times the 174 00:08:36.720 --> 00:08:38.960 mass of the Earth very very quickly. 175 00:08:39.200 --> 00:08:43.039 Why the rush and why specifically ten earth masses. 176 00:08:43.279 --> 00:08:46.480 Ten earth masses is roughly the threshold where the solid 177 00:08:46.519 --> 00:08:49.720 core's gravity becomes so intense that it can begin to 178 00:08:49.759 --> 00:08:52.879 hold on to the surrounding hydrogen and helium gas. 179 00:08:52.559 --> 00:08:54.919 Oh against the thermal pressure trying to push that gas 180 00:08:54.919 --> 00:08:56.080 away exactly. 181 00:08:56.440 --> 00:08:59.360 At first, it is a slow bleed. The core pulls 182 00:08:59.360 --> 00:09:02.799 in a thin envelope of gas, but as that envelope 183 00:09:02.840 --> 00:09:05.720 cools and compresses, it allows more gas. 184 00:09:05.440 --> 00:09:06.799 To fall in it's snowballing. 185 00:09:06.879 --> 00:09:09.720 It leads to a dramatic tipping point. Once the mass 186 00:09:09.720 --> 00:09:12.639 of the gas envelope equals the mass of the solid core, 187 00:09:12.840 --> 00:09:15.679 the planet undergoes runaway gas secretion. 188 00:09:15.519 --> 00:09:18.399 Runaway accretion. So it just violently vacuums up the rest of. 189 00:09:18.320 --> 00:09:22.600 The gas violently and rapidly. It vacuums up astronomical volumes 190 00:09:22.600 --> 00:09:25.519 of gas, swelling into a Jupiter sized giant in a 191 00:09:25.559 --> 00:09:28.000 fraction of the time it took to build the actual core. 192 00:09:28.240 --> 00:09:31.559 Okay, but earlier you mentioned an unforgiving time limit. Where 193 00:09:31.559 --> 00:09:34.519 does the ticking clock come into play during this runaway 194 00:09:34.559 --> 00:09:35.360 accretion phase? 195 00:09:36.000 --> 00:09:39.360 The clock is dictated by the host star itself, you see, 196 00:09:39.360 --> 00:09:43.279 a newborn star is wildly active. It emits fierce ultraviolet 197 00:09:43.320 --> 00:09:46.840 and X ray radiation along with these really powerful stellar. 198 00:09:46.480 --> 00:09:48.879 Winds, so it's blasting the disc constantly. 199 00:09:49.480 --> 00:09:53.519 These high energy photons bombard the surface of the protoplanetary disc, 200 00:09:53.720 --> 00:09:56.600 superheating the gas, and as the gas heats up, its 201 00:09:56.679 --> 00:09:58.559 fumble velocity increases. 202 00:09:58.039 --> 00:09:59.240 So it's too hot to hold onto. 203 00:09:59.440 --> 00:10:02.879 Eventually, yes, the gas molecules are moving so fast that 204 00:10:02.919 --> 00:10:06.720 they exceed the gravitational escape velocity of the entire star system. 205 00:10:06.840 --> 00:10:08.600 They just boil away into deep space. 206 00:10:08.679 --> 00:10:12.120 They do This process is called photo evaporation, and it 207 00:10:12.159 --> 00:10:15.279 will completely strip a typical system of its gas within 208 00:10:15.399 --> 00:10:17.279 roughly three to ten million years. 209 00:10:17.320 --> 00:10:20.240 Wow. Three to ten million years on a cosmic scale 210 00:10:20.320 --> 00:10:22.279 is like nothing. 211 00:10:22.399 --> 00:10:24.759 It's the blink of an eye. And once the gas 212 00:10:24.840 --> 00:10:28.559 is gone, the runaway accretion process is dead. If a 213 00:10:28.600 --> 00:10:31.639 solid core hasn't reached that ten earth mass threshold by 214 00:10:31.679 --> 00:10:34.519 the time the gas evaporates, it will forever remain a 215 00:10:34.639 --> 00:10:35.919 rocky or icy world. 216 00:10:36.000 --> 00:10:37.879 So that's why we have so many rocky worlds and 217 00:10:37.919 --> 00:10:39.320 so few gas giants. 218 00:10:39.519 --> 00:10:43.399 Exactly, building a giant requires threading an incredibly tight needle. 219 00:10:43.639 --> 00:10:46.120 You have to navigate the meter sized barrier, build a 220 00:10:46.159 --> 00:10:49.440 massive core, and trigger runaway accretion before the star blows 221 00:10:49.440 --> 00:10:50.919 all the raw materials into the void. 222 00:10:51.039 --> 00:10:54.039 Okay. That paints a remarkably chaotic and difficult picture of 223 00:10:54.039 --> 00:10:57.799 bottom up planet formation. It is a wildly inefficient process. 224 00:10:57.879 --> 00:10:58.639 Highly inefficient. 225 00:10:58.759 --> 00:11:01.720 Let's pivot to the second recipe then, because if accretion 226 00:11:01.879 --> 00:11:05.840 is a desperate race against the clock, the top down process, 227 00:11:05.919 --> 00:11:09.559 fragmentation feels like an entirely different category of physics. 228 00:11:09.639 --> 00:11:13.440 It is entirely different both in mechanism and in scale. 229 00:11:13.480 --> 00:11:16.519 While core accretion happens inside the disc around a star, 230 00:11:16.639 --> 00:11:20.200 fragmentation is typically the mechanism that forms the stars themselves. 231 00:11:20.320 --> 00:11:22.279 So we're talking about a much larger scale here. 232 00:11:22.440 --> 00:11:27.159 Massive we're talking about events that occur inside giant molecular clouds. 233 00:11:27.600 --> 00:11:33.519 These are unimaginably vast structures of cold, diffuse gas drifting 234 00:11:33.600 --> 00:11:36.360 in the interstellar medium like how big, oh, often spanning 235 00:11:36.480 --> 00:11:38.080 dozens of light years across. 236 00:11:38.279 --> 00:11:41.519 Okay, I am struggling to visualize how something that vast 237 00:11:41.559 --> 00:11:45.279 and diffuse turns into a dense, burning star. What actually 238 00:11:45.279 --> 00:11:46.759 initiates the colass. 239 00:11:46.519 --> 00:11:49.000 It all comes down to a battle between thermal pressure 240 00:11:49.039 --> 00:11:53.399 and gravity heat versus weight exactly. Even though the gas 241 00:11:53.399 --> 00:11:56.360 in a molecular cloud is incredibly cold, I mean, often 242 00:11:56.440 --> 00:11:59.919 just a few degrees above absolute zero, the molecule still 243 00:12:00.200 --> 00:12:01.120 possess thermal motion. 244 00:12:01.399 --> 00:12:02.399 Right, They're still vibrating. 245 00:12:02.559 --> 00:12:05.279 They vibrate and bounce off each other, creating an outward 246 00:12:05.279 --> 00:12:08.960 pressure that keeps the cloud inflated. However, these clouds are 247 00:12:08.960 --> 00:12:10.120 not perfectly uniform. 248 00:12:10.440 --> 00:12:11.519 They have lumpy bits. 249 00:12:11.840 --> 00:12:15.919 They have slightly denser pockets, yes, perhaps triggered by a 250 00:12:15.960 --> 00:12:19.399 passing shockwave from a distant supernova or even the galactic 251 00:12:19.440 --> 00:12:20.279 magnetic field. 252 00:12:20.480 --> 00:12:23.399 So gravity is trying to pull the pocket inward while 253 00:12:23.440 --> 00:12:25.399 the heat of the gas is trying to push it outward. 254 00:12:25.480 --> 00:12:28.000 You've got it, and there's a mathematical tipping point for this, 255 00:12:28.279 --> 00:12:31.559 known as the Genes mass, named after the British physicist 256 00:12:31.759 --> 00:12:32.480 James Jenes. 257 00:12:32.639 --> 00:12:33.840 The Genes mass, okay. 258 00:12:33.679 --> 00:12:36.080 The Gene's mass dictates that if a clump of gas 259 00:12:36.120 --> 00:12:39.440 reaches a certain critical density and is cold enough, the 260 00:12:39.559 --> 00:12:43.320 outward thermal pressure simply cannot support the inward pull of 261 00:12:43.320 --> 00:12:45.960 its own gravity. And when that happened, the moment that 262 00:12:45.960 --> 00:12:50.200 threshold is crossed, the entire clump becomes gravitationally unstable. It 263 00:12:50.360 --> 00:12:52.039 enters a state of freefall. 264 00:12:51.840 --> 00:12:55.960 A sudden, violent collapse, so not millions of years of 265 00:12:55.960 --> 00:13:00.000 gathering pebbles, but an instant structural failure of the cloud itself. 266 00:13:00.279 --> 00:13:03.600 The scale and speed are orders of magnitude different from accretion. 267 00:13:04.480 --> 00:13:08.960 As the pocket collapses, the material compresses, increasing the density. 268 00:13:08.559 --> 00:13:10.720 Which only accelerates the gravity exactly. 269 00:13:11.080 --> 00:13:14.919 The center of this collapsing fragment grows incredibly hot and dense, 270 00:13:15.279 --> 00:13:18.399 eventually igniting nuclear fusion and becoming. 271 00:13:18.039 --> 00:13:20.279 A star, and the leftovers form the disc. 272 00:13:20.840 --> 00:13:23.679 Right the remaining gas swirling around it flattens out into 273 00:13:23.720 --> 00:13:25.639 the protoplanetary disc we just discussed. 274 00:13:25.639 --> 00:13:28.200 Okay, but this creates a major logical hurdle for me. 275 00:13:28.720 --> 00:13:31.799 You just describe the process for making a star a 276 00:13:31.879 --> 00:13:33.679 massive nuclear fusing furnace. 277 00:13:33.799 --> 00:13:34.120 I did. 278 00:13:34.399 --> 00:13:37.679 But the object we are investigating today, twenty nine signy B, 279 00:13:38.279 --> 00:13:42.639 is definitively categorized as a planet. Why are astronomers even 280 00:13:42.720 --> 00:13:46.639 applying star formation physics to an object that orbits a star? 281 00:13:47.320 --> 00:13:49.799 And that is the core of the diagnostic muddy waters 282 00:13:49.799 --> 00:13:52.279 we find ourselves in today, Because, as it turns out, 283 00:13:52.320 --> 00:13:55.919 the universe doesn't restrict fragmentations solely to stellar nurseries. 284 00:13:56.120 --> 00:13:57.840 Wait, really, where else does it happen? 285 00:13:57.919 --> 00:14:01.120 Under very specific conditions, it is there uhetically possible for 286 00:14:01.200 --> 00:14:04.320 a localized version of fragmentation to occur within the outer 287 00:14:04.480 --> 00:14:09.120 tenuous edges of a protoplanetary disk itself. Inside the disk, 288 00:14:09.360 --> 00:14:13.960 astronomers call this disk instability or top down disk fragmentation. 289 00:14:14.480 --> 00:14:16.919 So you have the star already formed, you have the 290 00:14:16.960 --> 00:14:20.039 disc spinning around it, and instead of pebbles slowly gathering 291 00:14:20.080 --> 00:14:22.559 to make a planet, a massive chunk of the disk 292 00:14:22.759 --> 00:14:23.879 just suddenly collapses. 293 00:14:24.120 --> 00:14:29.080 Conceptually, yes, imagine the outer fringes of a massive, early 294 00:14:29.200 --> 00:14:33.600 stage protoplanetary disk. We're talking perhaps a billion miles or 295 00:14:33.639 --> 00:14:35.320 more away from the central star. 296 00:14:35.440 --> 00:14:37.000 Outward, it's incredibly cold. 297 00:14:37.000 --> 00:14:41.120 Exactly out there. The radiation from the star is incredibly weak. 298 00:14:41.559 --> 00:14:44.799 The gas in the disc is profoundly cold, which means 299 00:14:44.840 --> 00:14:47.240 its outward thermal pressure is very very. 300 00:14:47.080 --> 00:14:49.879 Low, so it's vulnerable to gravity, highly vulnerable. 301 00:14:50.080 --> 00:14:52.799 If the disc is massive enough, the sheer weight of 302 00:14:52.840 --> 00:14:56.720 the gas can trigger a localized gravitational instability. A large 303 00:14:56.759 --> 00:14:59.879 spiral arm or clump within the disc can suddenly fragment 304 00:15:00.039 --> 00:15:01.440 and collapse in on itself. 305 00:15:01.639 --> 00:15:03.000 Wow, and how long does that take? 306 00:15:03.200 --> 00:15:05.679 It forms a massive gaseous body in a matter of 307 00:15:05.799 --> 00:15:06.919 hundreds or thousands of. 308 00:15:06.960 --> 00:15:09.240 Years, oh wow, rather than millions exactly. 309 00:15:09.320 --> 00:15:12.240 It skips the rock gathering phase entirely. It just takes 310 00:15:12.240 --> 00:15:14.960 a massive bite out of the gas disc all at once. 311 00:15:15.120 --> 00:15:18.960 And because it formed so quickly, it completely bypasses the 312 00:15:19.000 --> 00:15:22.759 ticking clock of the star evaporating the disk precisely. 313 00:15:22.919 --> 00:15:26.240 Disc fragmentation is the leading theoretical explanation for why we 314 00:15:26.279 --> 00:15:31.120 occasionally find incredibly massive gas giant like objects orbiting at 315 00:15:31.159 --> 00:15:34.080 extreme distances from their host stars, which. 316 00:15:33.919 --> 00:15:36.919 Brings us directly to the paradox of twenty nine signey B. 317 00:15:37.679 --> 00:15:41.639 Because this object seems mathematically designed to frustrate both of 318 00:15:41.679 --> 00:15:44.240 these theories simultaneously. 319 00:15:43.440 --> 00:15:44.720 It is the perfect troublemaker. 320 00:15:44.799 --> 00:15:48.080 Let's look at the numbers. Lead researcher William Balmer and 321 00:15:48.120 --> 00:15:51.080 his team at Johns Hopkins zeroed in on twenty nine 322 00:15:51.080 --> 00:15:53.879 signey B because it sits at roughly fifteen times the 323 00:15:53.919 --> 00:15:56.799 massive Jupiter. Right now, I know that in the context 324 00:15:56.799 --> 00:16:00.200 of our solar system, fifteen jupiters is terrifyingly huge huge, 325 00:16:00.840 --> 00:16:03.679 But in the context of these two formation models. Why 326 00:16:03.799 --> 00:16:06.120 is that specific mass such a massive headache? 327 00:16:06.279 --> 00:16:09.759 Because fifteen jupiter masses represents the fulcrum point between the 328 00:16:09.840 --> 00:16:11.440 absolute limits of both theories. 329 00:16:11.519 --> 00:16:12.440 It's right on the boundary. 330 00:16:12.480 --> 00:16:14.840 It is a mass that should theoretically be impossible for 331 00:16:14.919 --> 00:16:16.679 either mechanism to comfortably achieve. 332 00:16:17.039 --> 00:16:20.559 Okay, let's start with the top down fragmentation model. Why 333 00:16:20.840 --> 00:16:22.799 is fifteen jupiter's a problem there? 334 00:16:22.919 --> 00:16:26.000 Well, when a cloud of gas collapses, whether it's in 335 00:16:26.039 --> 00:16:29.320 a molecular cloud or a disc, it creates a massive 336 00:16:29.360 --> 00:16:33.039 gravitational well, it naturally wants to gorge on the surrounding material. 337 00:16:33.200 --> 00:16:35.799 It's greedy, very greedy. It wants to become a star, 338 00:16:36.240 --> 00:16:39.639 or at least a brown dwarf, you know, a substellar 339 00:16:39.720 --> 00:16:44.399 object massive enough to fuse deuterium but not standard hydrogen. 340 00:16:44.600 --> 00:16:47.279 So a collapsing cloud doesn't just stop halfway. It pulls 341 00:16:47.279 --> 00:16:48.480 in everything it can reach. 342 00:16:48.600 --> 00:16:53.399 Exactly. The physical mechanics of fragmentation naturally produce massive objects. 343 00:16:53.879 --> 00:16:58.039 In hydrodynamic computer simulations, trying to get a fragmentation collapse 344 00:16:58.080 --> 00:17:01.039 to halt its growth at merely fifteen jupiter masses is 345 00:17:01.159 --> 00:17:02.240 incredibly difficult. 346 00:17:02.360 --> 00:17:03.200 Wants to keep growing. 347 00:17:03.600 --> 00:17:06.000 There is an opacity limit in the physics of collapse 348 00:17:06.039 --> 00:17:10.200 in gas that makes forming small fragments extremely inefficient. Fifteen 349 00:17:10.319 --> 00:17:13.960 jupiter masses is essentially the absolute floor. It's the lowest 350 00:17:14.000 --> 00:17:17.200 possible mass you could realistically expect a top down collapse 351 00:17:17.240 --> 00:17:17.759 to produce. 352 00:17:18.200 --> 00:17:23.440 It's the smallest possible star like collapse. Okay, but what 353 00:17:23.519 --> 00:17:26.279 about the bottom up accretion side. If it's the floor 354 00:17:26.319 --> 00:17:29.720 for fragmentation, how does it fit into the pebble gathering model. 355 00:17:29.880 --> 00:17:33.400 It acts as the absolute ceiling the ceiling. Yes, we 356 00:17:33.559 --> 00:17:36.799 establish that core accretion is a race against time to 357 00:17:36.880 --> 00:17:41.359 build a core, trigger runaway gas accretion, and swallow fifteen 358 00:17:41.440 --> 00:17:44.640 jupiter's worth of mass before the stars radiation boils the 359 00:17:44.680 --> 00:17:48.559 disc away. It basically stretches the timeline of physical models 360 00:17:48.599 --> 00:17:49.440 to their breaking point. 361 00:17:49.559 --> 00:17:50.880 The math just doesn't work out. 362 00:17:50.960 --> 00:17:55.000 Achieving fifteen jupiter masses through accretion requires a disk of 363 00:17:55.160 --> 00:18:00.480 unimaginable density, perfect conditions, and zero interruptions. It is the 364 00:18:00.519 --> 00:18:04.240 absolute highest mass a bottom up process could plausibly yield. 365 00:18:04.480 --> 00:18:07.319 I see the dilemma. You have an object sitting exactly 366 00:18:07.359 --> 00:18:10.119 on the razor's edge. It's either the smallest possible fragment 367 00:18:10.240 --> 00:18:11.599 or the largest possible. 368 00:18:11.240 --> 00:18:12.839 Creed stubbornly right in the middle. 369 00:18:13.240 --> 00:18:15.039 But I want to push back on the accretion theory 370 00:18:15.079 --> 00:18:17.640 here because we haven't factored in the orbital distance yet. 371 00:18:17.920 --> 00:18:20.960 Twenty nine signy B is one point five billion miles 372 00:18:20.960 --> 00:18:24.119 away from its host star, which is immense out at 373 00:18:24.119 --> 00:18:27.440 the distance of Uranus. The available material in a disk 374 00:18:27.759 --> 00:18:31.920 is incredibly sparse, right The dust and pebbles are spread 375 00:18:31.960 --> 00:18:33.559 over a massive volume. 376 00:18:33.240 --> 00:18:35.799 Of space, They are very thinly distributed. 377 00:18:35.400 --> 00:18:39.200 And orbital velocities are sluggish out there, meaning planetesimals aren't 378 00:18:39.200 --> 00:18:43.359 exactly sweeping through material very quickly. Doesn't that sheer distance 379 00:18:43.759 --> 00:18:47.839 almost entirely disqualify the slow bottom up process. 380 00:18:48.119 --> 00:18:51.359 Your intuition is aligned perfectly with the historical assumption of 381 00:18:51.400 --> 00:18:52.920 the astronomical. 382 00:18:52.240 --> 00:18:54.480 Community, so they thought the same thing they did. 383 00:18:54.960 --> 00:18:58.319 The standard model of core accretion dictates that building a 384 00:18:58.400 --> 00:19:00.920 ten earth mass core at a distance of one point 385 00:19:00.960 --> 00:19:05.000 five billion miles should take tens, perhaps hundreds of millions 386 00:19:05.000 --> 00:19:05.880 of years, But. 387 00:19:05.920 --> 00:19:09.279 The gas in the disk evaporates an under ten million exactly. 388 00:19:09.559 --> 00:19:13.200 The math simply does not close. Therefore, the long standing 389 00:19:13.200 --> 00:19:15.960 assumption has been that any massive object found at those 390 00:19:16.039 --> 00:19:19.559 extreme distances must be the result of sudden top down 391 00:19:19.599 --> 00:19:21.160 disc fragmentation. 392 00:19:20.799 --> 00:19:24.680 Because bottom up accretion shouldn't be physically capable of operating 393 00:19:24.720 --> 00:19:27.319 fast enough in that sparse, frozen environment. 394 00:19:27.480 --> 00:19:28.640 That was the accepted logic. 395 00:19:28.720 --> 00:19:32.400 Yes, but the Boemer team wasn't satisfied with a logical assumption. 396 00:19:32.720 --> 00:19:35.400 They didn't want to just guess that it was fragmentation 397 00:19:35.480 --> 00:19:36.400 based on the distance. 398 00:19:36.480 --> 00:19:37.640 Well. They wanted proof. 399 00:19:37.720 --> 00:19:41.799 They wanted definitive physical proof of how twenty nine signy 400 00:19:41.880 --> 00:19:44.799 view was constructed. And to get that proof, they couldn't 401 00:19:44.839 --> 00:19:46.920