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These are the user uploaded subtitles that are being translated: 1 00:00:01,302 --> 00:00:04,703 An invisible danger hurtles towards Earth 2 00:00:04,805 --> 00:00:07,539 at close to the speed of light. 3 00:00:07,608 --> 00:00:12,311 These are intergalactic alien interlopers on our Milky Way. 4 00:00:12,413 --> 00:00:13,846 Cosmic rays. 5 00:00:13,948 --> 00:00:16,415 Getting hit by a cosmic ray is like 6 00:00:16,550 --> 00:00:18,951 getting hit by a cosmic bullet. 7 00:00:19,053 --> 00:00:22,421 Cosmic rays are billions of times more energetic than any 8 00:00:22,556 --> 00:00:23,622 other types of particles, 9 00:00:23,757 --> 00:00:25,524 vastly more energetic than anything 10 00:00:25,626 --> 00:00:26,725 we can even create in 11 00:00:26,727 --> 00:00:30,129 a laboratory, in a nuclear fusion reactor, anywhere. 12 00:00:30,231 --> 00:00:33,065 They pierce spaceships, putting our astronauts 13 00:00:33,100 --> 00:00:34,199 in danger. 14 00:00:34,301 --> 00:00:36,702 But the source of their power is a mystery. 15 00:00:36,704 --> 00:00:38,637 Are they coming from other galaxies? 16 00:00:38,706 --> 00:00:40,506 Are they coming from things in between the galaxies? 17 00:00:40,508 --> 00:00:41,940 Where do cosmic rays come from? 18 00:00:42,042 --> 00:00:43,942 Truth is, the most powerful ones, 19 00:00:44,044 --> 00:00:45,210 we haven't got a clue. 20 00:00:45,312 --> 00:00:47,713 The race is on to solve the mystery 21 00:00:47,715 --> 00:00:50,816 of the fastest particles in the universe. 22 00:00:56,427 --> 00:00:58,638 DvX3M www.opensubtitles.org 23 00:01:05,533 --> 00:01:08,100 If I were to make a list of the dangers of space, 24 00:01:08,202 --> 00:01:10,102 it would be a long list. 25 00:01:10,104 --> 00:01:13,639 You know, there's hard vacuum, huge swings in temperatures, 26 00:01:13,707 --> 00:01:16,308 micro meteorites, all kinds of things. 27 00:01:16,410 --> 00:01:20,512 But probably at the very top of that list, cosmic rays. 28 00:01:20,614 --> 00:01:23,315 These space invaders are not what they seem. 29 00:01:23,417 --> 00:01:26,051 When you hear the name cosmic rays, 30 00:01:26,120 --> 00:01:27,820 you might think it's like a beam, 31 00:01:27,822 --> 00:01:30,322 like a laser beam of light. No, no, no, no, no, no. 32 00:01:30,324 --> 00:01:34,126 It's a tiny little death particle. 33 00:01:34,228 --> 00:01:35,227 To fight them, 34 00:01:35,229 --> 00:01:37,229 we must first understand them. 35 00:01:42,203 --> 00:01:44,203 April 2019. 36 00:01:45,940 --> 00:01:49,942 NASA's Parker probe flies closer to the sun than 37 00:01:50,010 --> 00:01:51,310 ever before. 38 00:01:51,312 --> 00:01:53,412 We know the sun produces some of 39 00:01:53,414 --> 00:01:56,615 the cosmic rays that fill the solar system, 40 00:01:56,617 --> 00:01:58,050 but we don't know how. 41 00:01:59,453 --> 00:02:05,124 Our sun looks like a beautiful glowing orb, 42 00:02:05,126 --> 00:02:08,327 bringing energy and light to Earth and allowing life 43 00:02:08,429 --> 00:02:09,661 to thrive. 44 00:02:09,730 --> 00:02:11,630 But if you look at it up close, 45 00:02:11,732 --> 00:02:14,633 you'll see a tumultuous storm of events. 46 00:02:16,103 --> 00:02:18,237 The amount of energy the sun is emitting every 47 00:02:18,305 --> 00:02:24,109 second is the equivalent of 100 billion one megaton bombs. 48 00:02:24,211 --> 00:02:25,444 It's a dangerous neighborhood. 49 00:02:26,614 --> 00:02:29,214 Suddenly, the probe is caught head-on 50 00:02:29,216 --> 00:02:30,916 in a powerful blast. 51 00:02:34,989 --> 00:02:37,322 It's perfectly positioned to monitor 52 00:02:37,424 --> 00:02:39,525 the outburst from the inside. 53 00:02:41,228 --> 00:02:44,463 The entire outer third of the sun is a boiling 54 00:02:44,565 --> 00:02:48,100 cauldron, and tied up in that plasma are magnetic fields. 55 00:02:48,102 --> 00:02:51,336 They get tied and twisted, and energy is stored in them, 56 00:02:51,405 --> 00:02:54,039 so they rise towards the surface, and there, 57 00:02:54,141 --> 00:02:57,309 they rearrange, they reconnect, they twist, they spin. 58 00:02:57,311 --> 00:03:00,345 When the magnetic field lines snap, 59 00:03:00,447 --> 00:03:03,649 energy bursts out. 60 00:03:03,750 --> 00:03:08,053 And sometimes, that energy release is explosive 61 00:03:08,121 --> 00:03:09,955 and that's what results in flares, 62 00:03:10,057 --> 00:03:11,657 which are these huge bursts of light. 63 00:03:13,060 --> 00:03:16,628 The probe discovers that after a solar flare, 64 00:03:16,730 --> 00:03:20,933 the sun's surface stores electrically charged particles. 65 00:03:21,035 --> 00:03:25,337 But sometimes, there's a second explosion called 66 00:03:25,406 --> 00:03:29,341 a coronal mass ejection, releasing superheated, 67 00:03:29,410 --> 00:03:32,444 electrically charged gas called plasma. 68 00:03:34,215 --> 00:03:37,749 These giant balls of plasma go flying off the surface of 69 00:03:37,818 --> 00:03:40,586 the sun, and in those balls of plasma 70 00:03:40,588 --> 00:03:43,222 are contained these charged particles. 71 00:03:45,826 --> 00:03:50,629 The charged particles move fast, but they hit a roadblock, 72 00:03:50,764 --> 00:03:53,065 a cloud of slower-moving particles 73 00:03:53,133 --> 00:03:56,802 that always surrounds the sun, the solar wind. 74 00:03:58,339 --> 00:04:01,440 Well, the coronal mass ejection is moving into the solar wind 75 00:04:01,541 --> 00:04:03,408 much faster than the wind is moving. 76 00:04:03,410 --> 00:04:07,112 So it sort of runs into it and creates this shockwave 77 00:04:07,114 --> 00:04:09,848 and ends up piling up particles at the edge. 78 00:04:09,983 --> 00:04:12,451 The shockwave and particles 79 00:04:12,519 --> 00:04:15,053 slam together -- In the collision, 80 00:04:15,155 --> 00:04:17,956 the particles steal energy and speed, 81 00:04:18,058 --> 00:04:20,626 like a baseball accelerating off a bat. 82 00:04:21,996 --> 00:04:26,265 The particles transform into something far more powerful -- 83 00:04:26,333 --> 00:04:28,834 A solar cosmic ray. 84 00:04:28,936 --> 00:04:31,036 They're light, but they're moving 85 00:04:31,105 --> 00:04:32,638 incredibly fast. 86 00:04:34,508 --> 00:04:37,843 The Earth is on average 93 million miles away from 87 00:04:37,945 --> 00:04:41,847 the sun, and these guys reach us in about an hour. 88 00:04:41,949 --> 00:04:43,548 That's 93 million miles an hour. 89 00:04:43,617 --> 00:04:45,617 That's pretty fast. 90 00:04:45,752 --> 00:04:48,820 The cosmic rays speed towards Earth. 91 00:04:48,955 --> 00:04:50,622 We're under attack. 92 00:04:50,691 --> 00:04:55,027 Cosmic rays are, by far, the most energetic 93 00:04:55,029 --> 00:04:58,730 particles that we know to exist in the universe. 94 00:04:58,832 --> 00:05:02,234 And when things with very high energy, no matter how small 95 00:05:02,303 --> 00:05:04,036 they are, impact something else, 96 00:05:04,137 --> 00:05:07,205 they deposit that energy, right, and so cosmic rays 97 00:05:07,207 --> 00:05:08,473 can be very dangerous. 98 00:05:08,475 --> 00:05:12,344 Solar cosmic rays aren't the only threat we face. 99 00:05:12,446 --> 00:05:16,748 Other space bullets arrive from beyond our solar system. 100 00:05:16,850 --> 00:05:18,917 There are different kinds of cosmic rays, 101 00:05:18,919 --> 00:05:21,753 just like there are different kinds of bullets. 102 00:05:21,822 --> 00:05:23,488 At the lowest end of the spectrum 103 00:05:23,624 --> 00:05:26,625 are these solar cosmic rays. 104 00:05:26,727 --> 00:05:29,761 These are like the BBs, and when a BB hits you, 105 00:05:29,830 --> 00:05:32,130 it might sting for a little bit, but you're not gonna get 106 00:05:32,132 --> 00:05:33,465 too worried about it. 107 00:05:33,533 --> 00:05:37,602 A bigger concern -- Galactic cosmic rays. 108 00:05:37,705 --> 00:05:41,039 They travel faster and have more energy. 109 00:05:41,141 --> 00:05:44,142 If solar rays are like BBs, 110 00:05:44,211 --> 00:05:47,312 the galactic cosmic rays are like rifle bullets. 111 00:05:47,414 --> 00:05:49,748 They're far more dangerous. 112 00:05:49,817 --> 00:05:51,750 They're moving a lot faster. 113 00:05:51,819 --> 00:05:54,419 But they're also more rare. 114 00:05:54,521 --> 00:05:57,022 Faster still are the universe's most wanted -- 115 00:05:57,024 --> 00:05:59,524 Ultra-high-energy cosmic rays. 116 00:05:59,593 --> 00:06:02,260 If you thought galactic cosmic rays were bad, it's 117 00:06:02,362 --> 00:06:05,731 because you haven't met an ultra-high-energy cosmic ray. 118 00:06:05,733 --> 00:06:08,834 These are the biggest, baddest, 119 00:06:08,936 --> 00:06:12,838 meanest cosmic rays in the universe. 120 00:06:13,941 --> 00:06:16,408 These ultra-high-energy cosmic rays 121 00:06:16,510 --> 00:06:18,310 are like hypersonic missiles. 122 00:06:18,312 --> 00:06:20,412 They are screaming, and they come from 123 00:06:20,514 --> 00:06:23,515 the most energetic events in the universe. 124 00:06:27,454 --> 00:06:29,621 The ultra-high-energy cosmic missiles 125 00:06:29,723 --> 00:06:32,824 are the rarest but also the swiftest. 126 00:06:34,128 --> 00:06:37,963 These cosmic ray particles are moving fast. 127 00:06:38,065 --> 00:06:40,799 These mysterious particles are moving incredibly 128 00:06:40,934 --> 00:06:42,300 close to the speed of light. 129 00:06:42,403 --> 00:06:45,036 I'm not talking about 99 percent the speed of light. 130 00:06:45,072 --> 00:06:46,505 They're moving through space at 131 00:06:46,507 --> 00:06:48,740 like 99.999... 132 00:06:48,809 --> 00:06:51,510 - 9999... - 9999... 133 00:06:51,512 --> 00:06:53,912 - 99999... - 999999... 134 00:06:53,914 --> 00:06:56,047 99999 -- 21 nines. 135 00:06:56,149 --> 00:06:57,315 That's fast. 136 00:06:57,317 --> 00:06:59,451 That's wild. That's scary. 137 00:07:01,155 --> 00:07:03,155 All three types of cosmic rays 138 00:07:03,223 --> 00:07:05,323 are racing through the solar system. 139 00:07:06,360 --> 00:07:10,228 If I were to hold up a golf ball in the middle of space, 140 00:07:10,230 --> 00:07:16,201 almost 100 cosmic rays pass through that golf ball every 141 00:07:16,203 --> 00:07:18,036 single second. 142 00:07:18,138 --> 00:07:21,873 It's a deadly hail of particle bullets, 143 00:07:21,875 --> 00:07:23,208 and out in space, 144 00:07:23,210 --> 00:07:26,945 our astronauts are caught in the crossfire. 145 00:07:27,047 --> 00:07:29,047 Cosmic rays represent one of 146 00:07:29,116 --> 00:07:32,517 the greatest dangers for human space flight. 147 00:07:32,619 --> 00:07:35,921 NASA plans to send astronauts back to the moon, 148 00:07:35,923 --> 00:07:37,422 where radiation levels -OVER RADIO: Lift-off. 149 00:07:37,524 --> 00:07:40,926 From cosmic rays are 200 times greater than 150 00:07:40,928 --> 00:07:43,962 on Earth, and that is just the start. 151 00:07:44,064 --> 00:07:47,599 One of NASA's big goals is to send humans to Mars, 152 00:07:47,601 --> 00:07:49,401 and that is a long way away, 153 00:07:49,536 --> 00:07:52,103 at least a six-month journey, and more often, 154 00:07:52,105 --> 00:07:54,840 about a nine-month journey. That's a big problem. 155 00:07:55,909 --> 00:08:00,645 I am hoping that one day, I can go to Mars as an astronaut, 156 00:08:00,747 --> 00:08:02,848 but I'm definitely afraid of cosmic rays, 157 00:08:02,950 --> 00:08:04,249 and the more that I read about it, 158 00:08:04,351 --> 00:08:06,418 the bigger of a threat it seems. 159 00:08:06,420 --> 00:08:11,056 So I think that NASA and other space organizations 160 00:08:11,124 --> 00:08:13,258 are going to need to work on 161 00:08:13,327 --> 00:08:15,494 how to protect their astronauts in these 162 00:08:15,496 --> 00:08:17,329 really dangerous situations. 163 00:08:19,132 --> 00:08:20,999 Only one group of people have been 164 00:08:21,001 --> 00:08:24,102 exposed to these high levels of cosmic rays, 165 00:08:25,305 --> 00:08:27,739 the crew members of the Apollo missions 166 00:08:29,109 --> 00:08:31,643 July 1969. 167 00:08:31,712 --> 00:08:35,447 That's one small step for man, 168 00:08:35,549 --> 00:08:38,116 one giant leap for mankind. 169 00:08:39,419 --> 00:08:41,953 One of the astronauts, Buzz Aldrin, 170 00:08:42,022 --> 00:08:44,422 sees something strange. 171 00:08:44,424 --> 00:08:45,724 During Apollo 11, 172 00:08:45,726 --> 00:08:48,226 Buzz Aldrin reported seeing tiny little 173 00:08:48,295 --> 00:08:50,962 flashes sometimes when he was looking around. 174 00:08:51,064 --> 00:08:52,831 That's pretty weird. 175 00:08:52,833 --> 00:08:55,200 But what's weirder is that he saw them 176 00:08:55,335 --> 00:08:57,202 when his eyes were closed. 177 00:08:57,337 --> 00:09:01,506 Later missions also report seeing odd flashes of light. 178 00:09:02,843 --> 00:09:05,310 A streak in the lower left side of the... 179 00:09:05,412 --> 00:09:06,912 left eye, moving down. 180 00:09:06,914 --> 00:09:11,716 The astronauts describe the flashes as spots, 181 00:09:11,718 --> 00:09:13,818 streaks, and clouds. 182 00:09:13,820 --> 00:09:17,422 Apollo 15 Commander David Scott reported seeing one that 183 00:09:17,524 --> 00:09:20,725 was blue with a white cast, like a blue diamond. 184 00:09:20,727 --> 00:09:25,630 What's happening is that a cosmic ray is entering 185 00:09:25,765 --> 00:09:26,798 the eyeball 186 00:09:26,800 --> 00:09:30,502 and then striking molecules and giving off 187 00:09:30,604 --> 00:09:32,637 a flash of light. 188 00:09:32,706 --> 00:09:36,341 An alternative theory is that it triggers the layer of 189 00:09:36,443 --> 00:09:38,944 sensitive cells in your retina, 190 00:09:39,046 --> 00:09:42,414 so you perceive a streak of light even though 191 00:09:42,416 --> 00:09:44,215 no light ever actually existed. 192 00:09:45,519 --> 00:09:48,219 The cosmic rays cause long-term damage. 193 00:09:48,322 --> 00:09:50,155 Inside of the eye's lens, 194 00:09:50,223 --> 00:09:52,891 there are these fiber cells that are transparent. 195 00:09:52,893 --> 00:09:54,859 Well, when a cosmic ray travels through them, 196 00:09:54,995 --> 00:09:57,562 it can damage those cells and make them cloudy, 197 00:09:57,631 --> 00:09:58,830 causing cataracts. 198 00:09:58,932 --> 00:10:01,433 When NASA examines ROWE: the astronauts' helmets, 199 00:10:01,534 --> 00:10:04,536 they find tiny tracks etched through them, 200 00:10:04,605 --> 00:10:07,405 evidence of cosmic ray impacts. 201 00:10:07,540 --> 00:10:10,642 When we say that cosmic rays are like tiny little bullets, 202 00:10:10,744 --> 00:10:13,011 we're not joking around. 203 00:10:13,013 --> 00:10:16,815 And some of these burrowed all the way through the helmet, 204 00:10:16,817 --> 00:10:20,952 which means it ended up in the astronaut's brain, 205 00:10:21,021 --> 00:10:24,322 which just makes me feel weird to think about. 206 00:10:24,424 --> 00:10:27,459 What might that long-term radiation 207 00:10:27,560 --> 00:10:30,562 do to your brain, to your ability to reason 208 00:10:30,630 --> 00:10:33,665 and problem solve in one of the most dangerous environments 209 00:10:33,700 --> 00:10:35,200 that humanity has ever placed itself? 210 00:10:36,403 --> 00:10:39,304 The farther we venture from our home planet, 211 00:10:39,306 --> 00:10:41,106 the more danger we face. 212 00:10:51,018 --> 00:10:54,819 Cosmic rays, highly energetic space particles, 213 00:10:54,821 --> 00:10:58,723 may be the most serious threat to human space exploration. 214 00:10:59,760 --> 00:11:02,927 The Hollywood conception of outer space is 215 00:11:02,929 --> 00:11:05,296 it's full of dangers like aliens 216 00:11:05,298 --> 00:11:08,099 wielding ray guns or black holes 217 00:11:08,201 --> 00:11:09,534 or asteroid showers. 218 00:11:09,603 --> 00:11:11,302 But in reality, the biggest 219 00:11:11,304 --> 00:11:13,938 danger facing astronauts is invisible. 220 00:11:14,007 --> 00:11:15,240 It's the cosmic radiation. 221 00:11:16,309 --> 00:11:19,811 Cosmic rays damaged ROWE: Apollo astronauts' eyes 222 00:11:19,913 --> 00:11:22,747 after just a few days' exposure. 223 00:11:22,816 --> 00:11:26,651 A one-way trip to Mars takes nine months. 224 00:11:26,720 --> 00:11:28,319 Future missions are going to be 225 00:11:28,321 --> 00:11:30,455 spending much longer times in space, 226 00:11:30,557 --> 00:11:31,656 which means we really need to 227 00:11:31,758 --> 00:11:34,726 consider how cosmic rays will impact us. 228 00:11:34,728 --> 00:11:38,830 We don't understand all the long-term effects 229 00:11:38,832 --> 00:11:42,801 from a steady rain of cosmic rays, 230 00:11:42,903 --> 00:11:46,104 but the astronauts are gonna have to deal with it. 231 00:11:46,206 --> 00:11:48,707 To find out more, scientists bombarded 232 00:11:48,709 --> 00:11:52,711 human cells with manmade cosmic ray particles. 233 00:11:52,713 --> 00:11:58,450 They discovered cosmic rays physically cut through DNA, 234 00:11:58,551 --> 00:12:00,719 chopping it apart. 235 00:12:00,721 --> 00:12:04,756 Damage to DNA in your cell is 236 00:12:04,858 --> 00:12:09,260 by far the worst kind, because your DNA 237 00:12:09,362 --> 00:12:11,830 is the cell's operating manuals, the blueprints 238 00:12:11,832 --> 00:12:15,800 so the cell knows how it should be functioning normally. 239 00:12:15,802 --> 00:12:17,836 You can trigger that cell to 240 00:12:17,938 --> 00:12:21,306 turn tumorous, to start producing cancer. 241 00:12:23,110 --> 00:12:26,311 In 2019, scientists ROWE: took the experiment 242 00:12:26,313 --> 00:12:29,114 further and simulated a trip to Mars... 243 00:12:30,117 --> 00:12:32,550 for mice -- For six months, 244 00:12:32,619 --> 00:12:34,652 they blasted the rodents with a steady 245 00:12:34,721 --> 00:12:38,757 stream of lab-made cosmic ray particles. 246 00:12:38,858 --> 00:12:42,460 The experiment found profound alterations 247 00:12:42,529 --> 00:12:45,430 to the mice's normal behavior. 248 00:12:45,565 --> 00:12:49,100 They learned new tasks much more slowly. 249 00:12:49,202 --> 00:12:50,602 Their memory was affected, and they 250 00:12:50,604 --> 00:12:53,638 forgot things they had already learned. 251 00:12:53,707 --> 00:12:55,440 They were more anxious and prone to 252 00:12:55,542 --> 00:12:58,910 giving up on tasks they'd normally complete. 253 00:12:58,912 --> 00:13:01,312 If you put some of these irradiated mice into 254 00:13:01,447 --> 00:13:05,617 a swimming test, rather than trying to swim to safety, 255 00:13:05,619 --> 00:13:07,218 many of them just simply gave up. 256 00:13:09,055 --> 00:13:10,722 This is important, because we need 257 00:13:10,824 --> 00:13:13,124 our astronauts to be fully functioning. 258 00:13:13,126 --> 00:13:16,628 The reason why you do crewed missions is because 259 00:13:16,730 --> 00:13:20,832 the human brain is much better than any computer. 260 00:13:20,934 --> 00:13:23,134 If even one of them has a problem, 261 00:13:23,203 --> 00:13:26,204 it can even put the mission and their lives in jeopardy. 262 00:13:27,707 --> 00:13:31,109 Other studies discover cosmic rays can accelerate 263 00:13:31,211 --> 00:13:35,313 aging, alter genes, and cause cardiovascular disease. 264 00:13:37,050 --> 00:13:38,850 That sounds bad enough, 265 00:13:38,952 --> 00:13:41,953 but there's a more immediate danger. 266 00:13:42,022 --> 00:13:44,789 When cosmic rays penetrate spaceships, 267 00:13:44,791 --> 00:13:47,926 they can fry electronic systems, and that's enough to 268 00:13:47,928 --> 00:13:49,561 jeopardize a mission. 269 00:13:49,629 --> 00:13:54,899 Our operations in space depend on electronics, on computers. 270 00:13:54,901 --> 00:13:59,604 And the worst case scenario is that the wrong cosmic ray comes 271 00:13:59,706 --> 00:14:01,639 at the wrong time and hits 272 00:14:01,741 --> 00:14:06,344 the wrong circuit, and it leads to a cascading series of 273 00:14:06,446 --> 00:14:10,014 failures that can totally jeopardize a mission. 274 00:14:11,051 --> 00:14:13,918 We see evidence of this onslaught in mission cameras. 275 00:14:15,255 --> 00:14:17,121 Even when we have a detector in space 276 00:14:17,257 --> 00:14:18,823 like on the Hubble Space Telescope, 277 00:14:18,925 --> 00:14:20,358 if you saw a raw image, 278 00:14:20,460 --> 00:14:23,061 it doesn't look like the beautiful images 279 00:14:23,129 --> 00:14:24,329 that are shown to the public. 280 00:14:24,464 --> 00:14:26,865 They're just crossed with cosmic rays, and those 281 00:14:26,966 --> 00:14:31,202 cosmic rays are destroying that detector slowly over time. 282 00:14:33,106 --> 00:14:36,040 So how can we protect astronauts and their equipment? 283 00:14:37,444 --> 00:14:39,711 The obvious answer is to add shielding. 284 00:14:41,715 --> 00:14:45,049 It's one thing to say like, just add more stuff. 285 00:14:45,151 --> 00:14:48,820 But have you seen rocket launches and how hard they are, 286 00:14:48,922 --> 00:14:51,823 how expensive it is to get stuff up into space? 287 00:14:53,226 --> 00:14:55,960 NASA does have a plan. 288 00:14:56,062 --> 00:14:58,763 The spacecraft for the Artemis moon landing mission 289 00:14:58,831 --> 00:15:02,033 will be packed for optimum cosmic ray protection. 290 00:15:02,102 --> 00:15:05,036 So one of the ways you can get around 291 00:15:05,138 --> 00:15:08,306 the mass limit is to basically get dual use 292 00:15:08,408 --> 00:15:10,041 out of everything -- Your supplies, 293 00:15:10,110 --> 00:15:13,811 your fuel, your water, and you can use those as shielding. 294 00:15:13,813 --> 00:15:15,813 But it's not that simple. 295 00:15:15,815 --> 00:15:19,017 Just as more powerful bullets penetrate armor, 296 00:15:19,019 --> 00:15:22,353 more energetic cosmic rays pierce the shielding 297 00:15:22,422 --> 00:15:24,022 on spaceships. 298 00:15:24,024 --> 00:15:26,124 The solar ones -- Yeah, you can just put up some 299 00:15:26,259 --> 00:15:28,960 material, some shielding, and it'll generally block them. 300 00:15:29,062 --> 00:15:31,863 But the higher energy ones, they can just burrow 301 00:15:31,998 --> 00:15:33,197 on through. 302 00:15:33,233 --> 00:15:37,302 If they hit one of the atoms in the shielding that is 303 00:15:37,404 --> 00:15:38,836 protecting our astronauts, 304 00:15:38,938 --> 00:15:42,040 it can create a shower of particles. 305 00:15:42,141 --> 00:15:44,709 That radiation particle might have missed 306 00:15:44,811 --> 00:15:46,210 any of the cells in your body. 307 00:15:46,313 --> 00:15:47,645 But you've now turned it into 308 00:15:47,747 --> 00:15:51,549 a blast, shredding through everything in the spacecraft. 309 00:15:51,618 --> 00:15:55,687 And so it turns out your shielding becomes 310 00:15:55,689 --> 00:15:59,223 the weapon that the cosmic rays use against you. 311 00:15:59,325 --> 00:16:04,529 But NASA is recruiting an unexpected ally -- the sun. 312 00:16:04,631 --> 00:16:09,300 Can we protect our astronauts by fighting fire with fire? 313 00:16:17,911 --> 00:16:22,413 Powerful cosmic rays smash through spaceships. 314 00:16:22,515 --> 00:16:27,518 But how can objects smaller than an atom carry enough 315 00:16:27,653 --> 00:16:30,455 energy to be dangerous to astronauts? 316 00:16:30,556 --> 00:16:33,424 Moving objects carry energy. 317 00:16:33,526 --> 00:16:35,960 We call this kinetic energy, and when 318 00:16:36,029 --> 00:16:39,530 they strike something, they transform that energy. 319 00:16:40,934 --> 00:16:44,202 When I hit my hand, the kinetic energy of 320 00:16:44,337 --> 00:16:49,640 my fist transforms into sound and heat and vibration. 321 00:16:49,709 --> 00:16:51,743 My hand hurts a little from 322 00:16:51,811 --> 00:16:55,613 that impact, from the transformation of energy. 323 00:16:55,715 --> 00:16:58,149 It's the same thing with cosmic rays. 324 00:16:58,218 --> 00:17:02,253 When they slam into a human brain cell or a computer chip, 325 00:17:02,355 --> 00:17:04,956 they dump some energy, causing damage. 326 00:17:06,326 --> 00:17:09,727 How much damage depends on their kinetic energy, 327 00:17:09,729 --> 00:17:12,063 and that comes down to two things -- 328 00:17:12,132 --> 00:17:13,965 Mass and speed. 329 00:17:15,001 --> 00:17:18,936 Intuitively, things that are moving at the same speed, 330 00:17:19,038 --> 00:17:21,406 if they're more massive, they carry more energy. 331 00:17:21,408 --> 00:17:23,941 A bigger asteroid slamming into Earth will 332 00:17:24,010 --> 00:17:26,711 do more damage than a smaller asteroid. 333 00:17:26,813 --> 00:17:29,414 If you double the mass of an object, 334 00:17:29,516 --> 00:17:32,316 its kinetic energy also doubles. 335 00:17:32,318 --> 00:17:35,053 Although mass is important, 336 00:17:35,154 --> 00:17:36,721 it's not as important as speed. 337 00:17:39,626 --> 00:17:42,727 Speed matters even more than mass. 338 00:17:42,729 --> 00:17:46,064 The kinetic energy depends directly on the mass, 339 00:17:46,132 --> 00:17:48,699 but it depends on the square of the speed. 340 00:17:48,701 --> 00:17:51,402 Here's what that means -- You double the mass, 341 00:17:51,404 --> 00:17:54,439 you have double the kinetic energy, you double the speed, 342 00:17:54,540 --> 00:17:56,808 you have four times the kinetic energy. 343 00:17:59,712 --> 00:18:05,650 When it comes to speed, cosmic rays are the elite. 344 00:18:05,751 --> 00:18:07,919 An ultra-high-energy cosmic ray 345 00:18:07,921 --> 00:18:12,523 detected in 1991 hit the atmosphere so fast, 346 00:18:12,525 --> 00:18:15,960 scientists called it the "My God Particle." 347 00:18:19,232 --> 00:18:22,500 This particle was higher energy than they thought 348 00:18:22,602 --> 00:18:24,335 they would ever, ever see. 349 00:18:24,437 --> 00:18:27,805 Until this fluorescent streak in the Utah sky, 350 00:18:27,907 --> 00:18:31,209 no one believed a particle could reach the Earth traveling 351 00:18:31,211 --> 00:18:33,311 so close to the speed of light, 352 00:18:33,313 --> 00:18:36,614 making cosmic ray particles far more dangerous 353 00:18:36,716 --> 00:18:37,949 than expected. 354 00:18:38,050 --> 00:18:40,218 As you approach the speed of light, 355 00:18:40,320 --> 00:18:42,753 energy, momentum, mass, they start 356 00:18:42,822 --> 00:18:44,722 to act a little bit differently. 357 00:18:44,857 --> 00:18:47,525 Einstein's equations of relativity become important, 358 00:18:47,627 --> 00:18:50,328 because the physics changes, and the energy it has 359 00:18:50,463 --> 00:18:53,464 becomes much, much, much stronger. 360 00:18:53,533 --> 00:18:56,400 If a particle is moving at close to the speed of light, 361 00:18:56,402 --> 00:19:00,505 that means that its energy is almost at the maximum allowed 362 00:19:00,607 --> 00:19:02,607 by the laws of physics. 363 00:19:04,711 --> 00:19:06,811 It's amazing to think that something as tiny as 364 00:19:06,813 --> 00:19:09,814 a proton could actually be dangerous to a human being. 365 00:19:09,949 --> 00:19:13,217 But amazingly, that proton is moving so fast, 366 00:19:13,319 --> 00:19:15,586 it carries as much energy as a baseball 367 00:19:15,588 --> 00:19:17,255 thrown at 100 miles an hour. 368 00:19:17,323 --> 00:19:21,159 A baseball contains over a trillion, trillion protons. 369 00:19:21,260 --> 00:19:25,229 Imagine all that energy carried by just one particle. 370 00:19:25,331 --> 00:19:29,200 So now you get a sense of just how risky these can be. 371 00:19:29,202 --> 00:19:31,602 Ultra-high-energy cosmic rays like 372 00:19:31,704 --> 00:19:35,706 the My God Particle are like supersonic missiles. 373 00:19:35,708 --> 00:19:38,609 They are the fastest, but they're so rare, 374 00:19:38,711 --> 00:19:41,812 astronauts are unlikely to be hit by one. 375 00:19:41,915 --> 00:19:46,017 Solar cosmic rays are like BB pellets -- abundant, 376 00:19:46,019 --> 00:19:48,719 but our spacecraft can block them. 377 00:19:48,788 --> 00:19:50,454 The biggest threat to our astronauts, 378 00:19:50,523 --> 00:19:53,124 however, are galactic cosmic rays. 379 00:19:53,226 --> 00:19:56,127 They come from elsewhere in the Milky Way. 380 00:19:56,129 --> 00:19:57,862 The combination of their speed 381 00:19:57,997 --> 00:20:01,599 and frequency makes them the most dangerous. 382 00:20:01,601 --> 00:20:05,703 These galactic cosmic rays are much more powerful than 383 00:20:05,705 --> 00:20:07,405 the solar cosmic rays, 384 00:20:07,507 --> 00:20:10,808 and they've traveled enormous distances 385 00:20:10,810 --> 00:20:13,544 to mess you up. 386 00:20:13,613 --> 00:20:18,015 Luckily, our astronauts have a surprising protector, 387 00:20:18,017 --> 00:20:21,619 a guardian of the solar system, the sun. 388 00:20:23,156 --> 00:20:24,622 As well as spitting out these 389 00:20:24,724 --> 00:20:29,126 high-energy solar cosmic ray particles, 390 00:20:29,128 --> 00:20:33,431 the sun is also streaming out lots of much lower energy 391 00:20:33,499 --> 00:20:36,033 particles of the solar wind. 392 00:20:36,135 --> 00:20:38,202 That outward moving solar wind acts 393 00:20:38,204 --> 00:20:41,772 as a force field, and the cosmic rays have to work 394 00:20:41,774 --> 00:20:47,011 their way upstream to get to Earth far inside this bubble. 395 00:20:47,013 --> 00:20:51,716 The solar wind extends 11 billion miles 396 00:20:51,818 --> 00:20:53,117 around the solar system, 397 00:20:53,252 --> 00:20:57,121 generating a magnetic field that repels incoming 398 00:20:57,123 --> 00:20:59,423 galactic cosmic rays. 399 00:20:59,525 --> 00:21:01,892 It's almost like the deflector shield 400 00:21:01,894 --> 00:21:04,128 of the Starship Enterprise. 401 00:21:04,130 --> 00:21:08,933 So the sun's magnetic field partially helps protect 402 00:21:09,002 --> 00:21:11,335 the Earth and any astronauts 403 00:21:11,404 --> 00:21:12,803 from the incoming radiation. 404 00:21:12,905 --> 00:21:16,707 Not long ago, our Voyager spacecraft 405 00:21:16,809 --> 00:21:19,944 made it to that boundary between the sun's bubble 406 00:21:20,046 --> 00:21:21,445 and the galaxy and was able 407 00:21:21,547 --> 00:21:24,649 to study that region, and we see the difference between 408 00:21:24,750 --> 00:21:27,518 inside the sun's bubble and what's going on 409 00:21:27,520 --> 00:21:29,120 outside the sun's bubble. 410 00:21:29,122 --> 00:21:31,522 The sun has our back, billions 411 00:21:31,624 --> 00:21:34,659 of miles away, and that's pretty cool. 412 00:21:34,760 --> 00:21:37,828 The Voyager space probes discovered 413 00:21:37,830 --> 00:21:40,665 a moving battlefield. 414 00:21:40,733 --> 00:21:44,602 The solar wind behaves a bit like a storm front on Earth. 415 00:21:44,604 --> 00:21:46,504 Sometimes, it advances. 416 00:21:46,506 --> 00:21:48,739 Sometimes, it retreats. 417 00:21:49,809 --> 00:21:51,809 When the sun's activity is the highest, 418 00:21:51,911 --> 00:21:54,812 it's spitting out more solar energetic protons, 419 00:21:54,914 --> 00:21:58,749 but those solar cosmic rays are much less damaging 420 00:21:58,818 --> 00:22:00,017 than the galactic ones, 421 00:22:00,019 --> 00:22:02,520 so the net is a benefit. 422 00:22:03,690 --> 00:22:06,524 So actually, ironically, you might find that, 423 00:22:06,526 --> 00:22:10,127 for astronauts, it is safer to launch missions to Mars 424 00:22:10,129 --> 00:22:14,065 during a period of higher solar activity, because although 425 00:22:14,133 --> 00:22:18,602 you have more of the solar particle radiation, 426 00:22:18,604 --> 00:22:22,106 you also get a better shielding effect 427 00:22:22,108 --> 00:22:23,808 from the solar wind. 428 00:22:23,810 --> 00:22:25,843 The sun's activity goes through 429 00:22:25,945 --> 00:22:28,412 an 11-year cycle of highs and lows. 430 00:22:28,414 --> 00:22:32,116 The protective bubble follows the same cycle, 431 00:22:32,118 --> 00:22:36,620 allowing NASA to predict the safest times to launch. 432 00:22:36,622 --> 00:22:38,522 This is a thorny problem, and, you know, 433 00:22:38,624 --> 00:22:41,759 we have very smart people working on it, but we want to 434 00:22:41,861 --> 00:22:44,228 explore space as much as we can, 435 00:22:44,230 --> 00:22:45,830 but we have to lower the risk 436 00:22:45,932 --> 00:22:47,832 to the astronauts as much as possible. 437 00:22:49,936 --> 00:22:53,437 NASA's fight against the cosmic invaders continues, 438 00:22:53,506 --> 00:22:56,240 but the biggest mystery remains. 439 00:22:56,309 --> 00:22:59,744 What exactly is launching the deadliest 440 00:22:59,812 --> 00:23:02,046 galactic cosmic rays? 441 00:23:10,323 --> 00:23:12,923 Every second, quadrillions of bits 442 00:23:12,925 --> 00:23:15,359 of space shrapnel race towards Earth 443 00:23:15,428 --> 00:23:17,361 at close to the speed of light -- 444 00:23:17,430 --> 00:23:20,030 Galactic cosmic rays. 445 00:23:21,100 --> 00:23:24,402 The galactic cosmic rays are like a rifle bullet. 446 00:23:24,404 --> 00:23:27,405 You do not want to get hit by one of these. 447 00:23:27,540 --> 00:23:31,308 They are invaders from outside the solar system. 448 00:23:31,411 --> 00:23:34,044 We know they're made by something powerful 449 00:23:34,113 --> 00:23:35,413 within our galaxy, 450 00:23:35,415 --> 00:23:39,049 so the source should be easy to detect. 451 00:23:39,151 --> 00:23:41,552 You'd think if one of them 452 00:23:41,654 --> 00:23:44,321 hits a detector on Earth, that we'd just be able 453 00:23:44,424 --> 00:23:46,056 to point back in a straight line and say, 454 00:23:46,125 --> 00:23:47,291 "It came from over there." 455 00:23:47,326 --> 00:23:49,126 And then look, is there something else over there, 456 00:23:49,128 --> 00:23:51,028 like a supernova explosion that 457 00:23:51,030 --> 00:23:52,963 could explain the source of this? 458 00:23:53,032 --> 00:23:55,599 The problem is that cosmic rays get 459 00:23:55,601 --> 00:24:00,004 bent as they move by magnetic fields. 460 00:24:00,006 --> 00:24:01,939 The electric charge on a cosmic ray 461 00:24:02,041 --> 00:24:04,108 makes it act like a little magnet, 462 00:24:05,178 --> 00:24:08,045 and the Milky Way is full of other magnets. 463 00:24:08,114 --> 00:24:12,249 If I'm a cosmic ray just barreling through the galaxy, 464 00:24:12,351 --> 00:24:14,752 and I encounter a magnetic field, 465 00:24:14,821 --> 00:24:17,121 I'm gonna slightly change directions. 466 00:24:17,223 --> 00:24:20,224 Maybe here, maybe there, maybe up there. 467 00:24:20,226 --> 00:24:23,260 My trajectory is going to become scrambled. 468 00:24:23,329 --> 00:24:25,963 And after a few million years or so, 469 00:24:26,065 --> 00:24:28,732 basically all the information about where it started has 470 00:24:28,801 --> 00:24:30,334 been lost -- It's going in a completely 471 00:24:30,403 --> 00:24:34,305 random direction for all practical purposes. 472 00:24:34,407 --> 00:24:38,309 But galactic cosmic rays also have a sidekick, 473 00:24:38,411 --> 00:24:44,048 one that is far less elusive -- Gamma rays. 474 00:24:44,149 --> 00:24:47,351 When a galactic cosmic ray hits a regular atom out 475 00:24:47,453 --> 00:24:50,321 in space, it causes this big reaction. 476 00:24:51,624 --> 00:24:53,891 It emits all sorts of other particles, 477 00:24:53,893 --> 00:24:55,226 including gamma rays, 478 00:24:55,361 --> 00:24:58,729 which are basically extremely energetic photons of light. 479 00:24:58,831 --> 00:25:02,700 Critically, gamma rays don't get bent by magnetic fields, 480 00:25:02,835 --> 00:25:04,502 because they don't have an electric charge, 481 00:25:04,604 --> 00:25:07,538 so they just beeline off in a straight line along whatever 482 00:25:07,640 --> 00:25:10,841 direction the cosmic ray was moving in the first place. 483 00:25:10,943 --> 00:25:14,945 So we can look back at where gamma rays are coming from in 484 00:25:15,014 --> 00:25:18,415 the sky, and that tells us where there are a lot of 485 00:25:18,417 --> 00:25:19,750 cosmic rays having collisions. 486 00:25:21,053 --> 00:25:24,855 And they've led us to a prime suspect... 487 00:25:26,125 --> 00:25:27,124 supernovas. 488 00:25:30,696 --> 00:25:31,962 Supernova are some of 489 00:25:32,064 --> 00:25:34,398 the most powerful explosions in the universe, 490 00:25:34,400 --> 00:25:37,434 and so they're ripe grounds for these highly energetic, 491 00:25:37,536 --> 00:25:41,705 extremely fast particles to be created. 492 00:25:41,807 --> 00:25:44,041 When a giant star runs out of fuel, 493 00:25:44,110 --> 00:25:46,977 it can no longer support its own weight. 494 00:25:46,979 --> 00:25:48,612 It collapses inward, 495 00:25:50,550 --> 00:25:54,051 triggering a huge explosion, powerful enough 496 00:25:54,120 --> 00:25:57,721 to smash atoms into tiny pieces. 497 00:25:57,723 --> 00:26:01,025 The explosion pushes out an expanding cloud 498 00:26:01,027 --> 00:26:04,828 of gas and dust, the supernova remnant. 499 00:26:04,830 --> 00:26:06,964 And that material, as it's moving out at 500 00:26:07,066 --> 00:26:08,165 1,000 miles a second, 501 00:26:08,233 --> 00:26:11,535 generates an incredibly powerful shockwave. 502 00:26:11,604 --> 00:26:14,038 And that shockwave could be where 503 00:26:14,106 --> 00:26:19,443 a particle swept up in the shock gets accelerated. 504 00:26:19,545 --> 00:26:22,012 The magnetic fields inside the cloud 505 00:26:22,014 --> 00:26:24,615 trap the subatomic particles. 506 00:26:24,684 --> 00:26:27,551 Cosmic rays inside of the supernova remnant 507 00:26:27,620 --> 00:26:29,453 are a lot like being in a pinball machine. 508 00:26:31,524 --> 00:26:35,526 So you have the shockwave as the flipper, and then your 509 00:26:35,528 --> 00:26:37,828 magnetic fields are these bumpers, 510 00:26:37,830 --> 00:26:40,064 prohibiting it from actually leaving. 511 00:26:41,434 --> 00:26:42,900 They're bouncing back and forth across 512 00:26:42,902 --> 00:26:45,903 this incredibly energetic shock, and each time 513 00:26:45,905 --> 00:26:47,037 they bounce back and forth, 514 00:26:47,106 --> 00:26:49,607 the key is they pick up a little more energy. 515 00:26:50,643 --> 00:26:53,944 When a galactic cosmic ray gains enough energy, 516 00:26:54,013 --> 00:26:57,281 the magnetic fields can no longer hold on to it. 517 00:26:57,283 --> 00:26:58,515 It escapes. 518 00:27:01,153 --> 00:27:03,821 The supernova theory explains the birth 519 00:27:03,823 --> 00:27:06,457 of many of these cosmic bullets. 520 00:27:06,558 --> 00:27:09,393 But then we discovered a super gamma ray 521 00:27:09,395 --> 00:27:13,130 so powerful, it must have a completely different 522 00:27:13,232 --> 00:27:14,565 origin story. 523 00:27:14,633 --> 00:27:17,501 So this gamma ray was incredibly high energy, 524 00:27:17,636 --> 00:27:20,804 which means that the cosmic ray responsible for it was 525 00:27:20,806 --> 00:27:23,540 probably also extremely high in energy. 526 00:27:23,642 --> 00:27:25,743 If you fire a bullet into a pinball machine, 527 00:27:25,778 --> 00:27:27,444 it's not gonna bounce back and forth. 528 00:27:29,248 --> 00:27:30,948 I'm just gonna break through the machinery. 529 00:27:31,050 --> 00:27:32,416 The problem is that these 530 00:27:32,418 --> 00:27:35,219 are vastly more energetic than that. 531 00:27:35,321 --> 00:27:38,122 So there's no way they could have been bouncing around all 532 00:27:38,124 --> 00:27:41,558 the way up to their current energies inside of that 533 00:27:41,627 --> 00:27:45,029 particular pinball machine. 534 00:27:45,031 --> 00:27:48,065 There must be something else in the Milky Way 535 00:27:48,133 --> 00:27:50,434 creating galactic cosmic rays, 536 00:27:50,503 --> 00:27:54,705 something more powerful than a supernova. 537 00:27:56,308 --> 00:27:59,510 The question is, what? 538 00:27:59,612 --> 00:28:03,047 January 2021. 539 00:28:03,148 --> 00:28:04,815 At an observatory 540 00:28:04,817 --> 00:28:07,818 high up on the side of a Mexican volcano, 541 00:28:07,820 --> 00:28:11,321 blue light zaps through water tanks, 542 00:28:12,425 --> 00:28:15,025 signs of incoming gamma rays. 543 00:28:16,829 --> 00:28:19,830 Their trail stretches back across the Milky Way, 544 00:28:19,832 --> 00:28:24,101 crossing billions of miles, but suddenly goes cold. 545 00:28:25,337 --> 00:28:28,439 Instead of originating in a huge explosion, 546 00:28:28,507 --> 00:28:33,444 the trail ends in a cold, sparse cloud of dust. 547 00:28:33,545 --> 00:28:36,714 Molecular clouds, at first glance, seem like 548 00:28:36,816 --> 00:28:38,315 one of the most boring, 549 00:28:38,317 --> 00:28:41,118 innocuous places in the universe. 550 00:28:41,220 --> 00:28:45,522 You can barely even see them without an infrared telescope. 551 00:28:45,524 --> 00:28:48,258 They're not events like supernova 552 00:28:48,360 --> 00:28:50,327 that have enormously high energies. 553 00:28:50,429 --> 00:28:52,463 So you wouldn't expect it to create super 554 00:28:52,531 --> 00:28:54,298 energetic particles. 555 00:28:54,300 --> 00:28:57,034 Something must be hidden in the cloud, 556 00:28:57,103 --> 00:29:01,405 something powerful enough to accelerate the cosmic rays. 557 00:29:01,407 --> 00:29:03,507 We just don't know what. 558 00:29:03,509 --> 00:29:06,410 We can't see inside the molecular clouds, 559 00:29:06,545 --> 00:29:09,747 so it could be that, deep inside them, 560 00:29:09,848 --> 00:29:13,317 there are clusters of newborn stars that are cranking out 561 00:29:13,419 --> 00:29:14,818 these cosmic rays, 562 00:29:14,820 --> 00:29:18,756 but we don't know if even the crankiest of stars are 563 00:29:18,824 --> 00:29:23,527 capable of producing cosmic rays at these energies. 564 00:29:23,529 --> 00:29:25,662 Just two months later, 565 00:29:25,764 --> 00:29:29,233 in March of 2021, we get another clue. 566 00:29:29,334 --> 00:29:31,935 Scientists detect gamma rays coming 567 00:29:32,037 --> 00:29:35,239 from the Cygnus Cocoon Nebula. 568 00:29:35,340 --> 00:29:37,941 It's a dense molecular cloud with 569 00:29:38,043 --> 00:29:41,612 a difference -- At the center is a cavity. 570 00:29:41,714 --> 00:29:46,450 Hundreds of closely packed stars push against the dust 571 00:29:46,552 --> 00:29:48,819 and gas, including 572 00:29:48,888 --> 00:29:52,856 huge bright stars called spectral type O and B 573 00:29:53,926 --> 00:29:56,160 Spectral type O and B stars are 574 00:29:56,228 --> 00:29:58,362 some of the hottest stars in our universe. 575 00:30:00,032 --> 00:30:02,599 The massive stars blast out solar winds far 576 00:30:02,734 --> 00:30:05,035 stronger than the wind produced by our sun. 577 00:30:06,705 --> 00:30:09,039 When you think about all these stars forming together, 578 00:30:09,141 --> 00:30:12,342 they are all putting off a wind of high-energy particles 579 00:30:12,444 --> 00:30:13,644 from their surfaces. 580 00:30:13,679 --> 00:30:16,713 These winds collide and form big shock structures 581 00:30:16,816 --> 00:30:18,649 between all of these young stars. 582 00:30:18,750 --> 00:30:20,951 You're getting so much energy from 583 00:30:21,053 --> 00:30:22,753 so many different winds, coming from so many 584 00:30:22,855 --> 00:30:27,357 different directions, that it forms a boiling mass of 585 00:30:27,426 --> 00:30:29,493 shockwaves and magnetic fields. 586 00:30:29,495 --> 00:30:30,961 It's a pinball machine 587 00:30:31,030 --> 00:30:34,965 on a far bigger scale -- The magnetic fields are stronger 588 00:30:35,034 --> 00:30:36,300 than a supernova's, 589 00:30:36,302 --> 00:30:40,604 trapping and accelerating the more energetic cosmic rays 590 00:30:40,606 --> 00:30:41,805 for longer. 591 00:30:41,807 --> 00:30:44,241 One important thing about star clusters is that 592 00:30:44,343 --> 00:30:47,010 they are around for millions and millions of years. 593 00:30:47,012 --> 00:30:49,947 It's not just a one-off event like a supernova. 594 00:30:49,982 --> 00:30:52,916 And so you've got this magnetic field 595 00:30:52,918 --> 00:30:56,119 and these shocks happening over a long period of time, 596 00:30:56,255 --> 00:30:58,522 and that may be what you need to accelerate cosmic rays. 597 00:30:59,925 --> 00:31:04,428 Molecular clouds may shoot out galactic cosmic rays, 598 00:31:04,530 --> 00:31:07,664 but what fires the hypersonic space missiles, 599 00:31:07,733 --> 00:31:10,801 the ultra-high-energy cosmic rays? 600 00:31:10,936 --> 00:31:14,805 The culprit may be hiding out in distant galaxies -- 601 00:31:14,940 --> 00:31:18,108 Supermassive black holes. 602 00:31:25,217 --> 00:31:27,517 Ultra-high-energy cosmic rays are 603 00:31:27,620 --> 00:31:31,221 the hypersonic missiles of the particle world. 604 00:31:31,290 --> 00:31:33,323 If a photon of light, the fastest thing in 605 00:31:33,325 --> 00:31:37,227 the universe, had a race with an ultra-high-energy cosmic ray, 606 00:31:37,329 --> 00:31:41,665 it would be so close, that after 200,000 years, 607 00:31:41,700 --> 00:31:44,501 that photon would be half an inch ahead of 608 00:31:44,636 --> 00:31:46,403 the ultra-high-energy cosmic ray. 609 00:31:46,405 --> 00:31:50,941 They appear to come from beyond our Milky Way galaxy. 610 00:31:51,043 --> 00:31:55,812 Our galaxy is 100,000 light years across. 611 00:31:55,915 --> 00:31:59,616 The next nearest galaxy to us is two million light years away. 612 00:31:59,718 --> 00:32:01,752 So these are traveling to us 613 00:32:01,853 --> 00:32:04,821 across millions and billions of light years. 614 00:32:04,924 --> 00:32:09,326 How do you accelerate this tiny 615 00:32:09,461 --> 00:32:13,964 little particle to such insane velocities? 616 00:32:14,066 --> 00:32:15,899 What is the power source? 617 00:32:15,901 --> 00:32:19,536 What in the universe has that kind of capability? 618 00:32:19,605 --> 00:32:22,406 Where's the Death Star here? 619 00:32:22,541 --> 00:32:25,142 Their speed makes them dangerous, 620 00:32:25,210 --> 00:32:29,046 but it also makes it easier to find their source. 621 00:32:29,114 --> 00:32:32,416 Ultra-high-energy cosmic rays are moving so rapidly, 622 00:32:32,551 --> 00:32:34,518 that they're really not affected that much by 623 00:32:34,620 --> 00:32:35,752 magnetic fields. 624 00:32:35,821 --> 00:32:38,021 It's like a bullet going through a fisherman's net. 625 00:32:38,023 --> 00:32:41,825 And so they're coming mostly in a straight line. 626 00:32:41,827 --> 00:32:44,161 When they're coming in a straight line, and we can point 627 00:32:44,229 --> 00:32:45,729 back to their origin, 628 00:32:45,731 --> 00:32:49,499 and that's something we can use to figure out where 629 00:32:49,501 --> 00:32:50,934 and how they're getting accelerated. 630 00:32:52,905 --> 00:32:54,604 In the Argentinian desert, 631 00:32:54,707 --> 00:32:58,241 the Pierre Auger Cosmic Ray Detector completes 632 00:32:58,310 --> 00:33:00,410 a 12-year study of the sky. 633 00:33:02,648 --> 00:33:05,549 It confirms that most galaxies have a supermassive 634 00:33:05,650 --> 00:33:07,351 black hole at their center, 635 00:33:07,419 --> 00:33:11,154 but only a few are active, shooting out energy. 636 00:33:11,256 --> 00:33:15,058 These active supermassive black holes also 637 00:33:15,127 --> 00:33:18,428 blast out ultra-high-energy cosmic rays. 638 00:33:19,431 --> 00:33:23,300 Supermassive black holes are already extremely powerful. 639 00:33:23,302 --> 00:33:25,035 So it makes a lot of sense to me that 640 00:33:25,137 --> 00:33:28,238 the ultra-high-energy cosmic rays could originate at 641 00:33:28,340 --> 00:33:30,440 supermassive black holes. 642 00:33:30,509 --> 00:33:35,712 The M87 galaxy is 54 million light years away. 643 00:33:35,714 --> 00:33:38,315 It's famous because we took a photo 644 00:33:38,317 --> 00:33:41,718 of the supermassive black hole at its core. 645 00:33:41,720 --> 00:33:45,989 So the event horizon telescope image of the swirling vortex of 646 00:33:45,991 --> 00:33:48,458 gas around that central black hole, 647 00:33:48,527 --> 00:33:50,560 that shadow that you can't actually see, 648 00:33:50,629 --> 00:33:55,432 that could be a site for the unbelievably energetic 649 00:33:55,534 --> 00:33:56,933 acceleration of cosmic rays. 650 00:33:57,035 --> 00:34:00,303 In March 2021, 651 00:34:00,305 --> 00:34:03,306 scientists analyze the data further. 652 00:34:03,442 --> 00:34:07,310 This new image of M87 shows very clear 653 00:34:07,446 --> 00:34:08,945 magnetic field lines, 654 00:34:09,048 --> 00:34:11,815 which is really stunning and reminds us of how much energy 655 00:34:11,917 --> 00:34:15,052 could be contained close to the supermassive black hole. 656 00:34:15,153 --> 00:34:17,821 Black holes have enormous power, 657 00:34:17,923 --> 00:34:20,924 but how do they transfer some of that energy 658 00:34:20,926 --> 00:34:22,159 to a tiny particle? 659 00:34:22,260 --> 00:34:25,328 One possibility for how supermassive black holes 660 00:34:25,464 --> 00:34:27,631 could accelerate such enormously energetic 661 00:34:27,733 --> 00:34:31,601 cosmic rays is that they actually drag or capture via 662 00:34:31,736 --> 00:34:32,936 their gravity 663 00:34:33,071 --> 00:34:36,406 preexisting normal cosmic rays, which are already 664 00:34:36,541 --> 00:34:37,841 extremely energetic, 665 00:34:37,943 --> 00:34:41,812 and then give them an extra boost to even higher energies. 666 00:34:41,914 --> 00:34:45,048 So supermassive black holes bend the fabric 667 00:34:45,117 --> 00:34:46,450 of spacetime around them, 668 00:34:46,551 --> 00:34:50,620 and even light particles can get stuck, and cosmic rays are 669 00:34:50,622 --> 00:34:53,657 no different -- they can also be attracted by the supermassive 670 00:34:53,758 --> 00:34:57,360 black holes and get drawn into their orbit. 671 00:34:57,462 --> 00:35:00,831 It makes sense that the black hole captures 672 00:35:00,833 --> 00:35:02,499 passing cosmic rays, 673 00:35:02,601 --> 00:35:05,635 but how do the particles escape its clutches 674 00:35:05,737 --> 00:35:07,104 and hurtle towards us? 675 00:35:08,474 --> 00:35:12,275 M87 has a fearsome weapon in its arsenal. 676 00:35:12,277 --> 00:35:17,314 Enormous jets of energy blast out of its poles. 677 00:35:17,316 --> 00:35:20,851 So M87's jets are spectacularly large, 678 00:35:20,986 --> 00:35:23,954 larger than the entire galaxy that houses this black hole 679 00:35:24,056 --> 00:35:25,422 that's launching those jets. 680 00:35:25,524 --> 00:35:28,158 The powerful jets may give the cosmic rays 681 00:35:28,193 --> 00:35:29,559 a speed injection, 682 00:35:29,661 --> 00:35:33,163 transforming them from galactic rifle bullets into 683 00:35:33,265 --> 00:35:36,500 ultra-high-energy hypersonic missiles. 684 00:35:36,602 --> 00:35:41,037 So imagine if you had a regular bullet that 685 00:35:41,139 --> 00:35:43,807 you fired out of a gun at high speed, 686 00:35:43,809 --> 00:35:47,944 and as its flying, a little rocket motor in 687 00:35:48,079 --> 00:35:52,315 the bullet kicks in and takes it up to even higher speeds. 688 00:35:52,317 --> 00:35:54,651 That's sort of what's happening to 689 00:35:54,753 --> 00:35:57,120 the cosmic rays in these jets. 690 00:35:58,457 --> 00:36:00,357 Black holes may be the supervillains 691 00:36:00,458 --> 00:36:02,025 we've been looking for, 692 00:36:02,027 --> 00:36:04,928 firing out the fastest cosmic bullets, 693 00:36:04,930 --> 00:36:08,899 but cosmic rays have a superpower of their own. 694 00:36:08,901 --> 00:36:10,400 They're time travelers. 695 00:36:18,110 --> 00:36:20,710 Cosmic rays race through the universe at close 696 00:36:20,845 --> 00:36:24,814 to the speed of light -- Like subatomic bullets, 697 00:36:24,917 --> 00:36:28,919 they can pierce spaceships and harm astronauts. 698 00:36:31,924 --> 00:36:34,624 But down on Earth, we're protected. 699 00:36:36,562 --> 00:36:41,698 Out of all of the rocky inner planets in the solar system, 700 00:36:41,700 --> 00:36:44,201 the Earth is the only one to generate 701 00:36:44,336 --> 00:36:48,305 its own deflector shield against this cosmic radiation. 702 00:36:48,373 --> 00:36:50,607 That's amazing. And that's where life is. 703 00:36:50,742 --> 00:36:54,211 I don't think that's actually all that much of a coincidence. 704 00:36:54,346 --> 00:36:58,048 The Earth creates its own magnetic field. 705 00:36:58,116 --> 00:37:01,218 The Earth has this wonderful active molten core of metal. 706 00:37:01,320 --> 00:37:04,788 All of that metal is moving around inside the Earth, 707 00:37:04,790 --> 00:37:07,557 and that moving metal generates a strong magnetic field. 708 00:37:07,659 --> 00:37:09,926 These cosmic rays are electrically charged. 709 00:37:09,928 --> 00:37:11,561 They follow a magnetic field. 710 00:37:11,663 --> 00:37:13,964 So our magnetic field deflects most 711 00:37:14,065 --> 00:37:15,932 of the cosmic rays around it. 712 00:37:16,034 --> 00:37:18,201 The shield is not perfect. 713 00:37:18,203 --> 00:37:21,271 Some cosmic rays do get through, 714 00:37:21,273 --> 00:37:24,307 but then they hit our second line of defense -- 715 00:37:24,309 --> 00:37:25,809 The atmosphere. 716 00:37:25,811 --> 00:37:27,844 One of the things we have to be thankful for is 717 00:37:27,979 --> 00:37:30,513 our atmosphere -- not only does it give us air to breathe, 718 00:37:30,649 --> 00:37:32,515 but it protects us from these space bullets. 719 00:37:32,517 --> 00:37:37,754 The atmosphere is like a missile defense system. 720 00:37:37,822 --> 00:37:40,624 Cosmic rays collide with air molecules, 721 00:37:40,626 --> 00:37:44,127 shattering into safer, smaller particles. 722 00:37:44,262 --> 00:37:48,365 The most common ones are called muons. 723 00:37:49,701 --> 00:37:54,204 The muons are the children of the cosmic rays. 724 00:37:54,306 --> 00:37:57,540 They're produced by these high-energy collisions 725 00:37:57,609 --> 00:37:58,908 in our upper atmosphere that 726 00:37:58,910 --> 00:38:02,545 create these showers of muons that then come down to 727 00:38:02,647 --> 00:38:03,779 the surface. 728 00:38:03,781 --> 00:38:06,016 There's as many as four of these cosmic rays passing 729 00:38:06,018 --> 00:38:07,617 through my hand every second. 730 00:38:07,619 --> 00:38:09,719 They're passing through your body right now. 731 00:38:09,788 --> 00:38:11,755 Muons are so abundant, 732 00:38:11,856 --> 00:38:14,824 we don't need a high-tech observatory to detect them, 733 00:38:14,959 --> 00:38:18,762 just a few things you'd find in a high school science lab. 734 00:38:18,830 --> 00:38:23,133 A small aquarium that I've attached a small piece of felt 735 00:38:23,234 --> 00:38:24,801 to the bottom. 736 00:38:24,803 --> 00:38:27,804 Some frozen carbon dioxide, some dry ice, 737 00:38:27,906 --> 00:38:33,810 hence the safety gloves, a flat piece of metal like this, 738 00:38:33,812 --> 00:38:35,645 some isopropyl alcohol. 739 00:38:37,416 --> 00:38:40,050 Then I flip the whole thing over 740 00:38:40,151 --> 00:38:43,320 onto the bottom, and I wait. 741 00:38:45,524 --> 00:38:49,526 So what's happening is that the alcohol in the felt is 742 00:38:49,528 --> 00:38:52,929 evaporating in sinking down, and because 743 00:38:52,931 --> 00:38:55,732 that bottom layer is so cold from the dry ice, 744 00:38:55,734 --> 00:39:00,136 it forms a super saturated cloud of alcohol vapor. 745 00:39:01,506 --> 00:39:05,308 When the charged particles pass through the cold vapor, 746 00:39:05,310 --> 00:39:09,713 they create tiny ghostly trails. 747 00:39:09,815 --> 00:39:12,615 What we're looking for are the muons, 748 00:39:12,617 --> 00:39:16,219 the subatomic particles generated when a cosmic ray 749 00:39:16,354 --> 00:39:18,722 strikes the upper atmosphere. 750 00:39:18,724 --> 00:39:21,825 Each silvery thread in the cloud chamber 751 00:39:21,960 --> 00:39:25,028 is the sign of a cosmic ray. 752 00:39:25,030 --> 00:39:28,898 These muons should never make it down to Earth at all. 753 00:39:28,900 --> 00:39:34,003 They only live for 2.2 microseconds before breaking up, 754 00:39:34,005 --> 00:39:35,705 not enough time to travel 755 00:39:35,807 --> 00:39:38,708 through six miles of Earth's atmosphere. 756 00:39:38,710 --> 00:39:41,845 Naively, we would think there's no way that a muon could make it 757 00:39:41,980 --> 00:39:44,147 from the upper atmosphere to where we are now 758 00:39:44,249 --> 00:39:45,215 without decaying. 759 00:39:45,217 --> 00:39:47,016 It turns out they do, and the only 760 00:39:47,018 --> 00:39:50,920 way they do this is they effectively time travel. 761 00:39:50,922 --> 00:39:54,424 The muons move at 98 percent the speed of light. 762 00:39:55,827 --> 00:39:57,527 They move so fast, 763 00:39:57,529 --> 00:40:01,064 they experience what Einstein called time dilation. 764 00:40:01,132 --> 00:40:04,734 Albert Einstein taught us that we live 765 00:40:04,803 --> 00:40:06,736 in a space time, and so that means 766 00:40:06,805 --> 00:40:10,340 that all measurements of lengths and durations of time 767 00:40:10,409 --> 00:40:11,941 are relative. 768 00:40:12,043 --> 00:40:13,810 From a muon's perspective, 769 00:40:13,912 --> 00:40:17,447 we humans move incredibly slowly. 770 00:40:17,516 --> 00:40:20,817 They're moving so fast that, for them, 771 00:40:20,819 --> 00:40:23,720 time is stretched out. 772 00:40:23,822 --> 00:40:27,857 What we found by measuring the energy and the lifetime of 773 00:40:27,959 --> 00:40:33,229 muons is that as muons got closer to the speed of light, 774 00:40:33,331 --> 00:40:37,734 their lifetime increased, because to them, time is 775 00:40:37,803 --> 00:40:41,237 slowing down, exactly the way Einstein predicted. 776 00:40:41,339 --> 00:40:45,408 Their lifespan is extended by more than 20 times 777 00:40:45,410 --> 00:40:46,609 from our perspective, 778 00:40:46,711 --> 00:40:49,012 so they make it to the ground. 779 00:40:51,950 --> 00:40:55,952 Cosmic rays are the ultimate space travelers. 780 00:40:56,054 --> 00:40:59,722 They're awe-inspiring speed allows us to unlock 781 00:40:59,825 --> 00:41:03,426 hidden processes and test our theories of physics. 782 00:41:04,729 --> 00:41:06,463 They're way more energetic than anything 783 00:41:06,531 --> 00:41:08,465 we can do in a laboratory on Earth. 784 00:41:08,533 --> 00:41:10,400 So that means we can unlock all kinds of 785 00:41:10,502 --> 00:41:13,036 new domains about physics at the highest, 786 00:41:13,137 --> 00:41:15,238 most extreme energies. 787 00:41:15,307 --> 00:41:17,874 They're our best link to the farthest reaches of 788 00:41:17,876 --> 00:41:19,642 the cosmos. 789 00:41:19,711 --> 00:41:23,446 To me, it's really exciting that we're actually sampling 790 00:41:23,548 --> 00:41:26,316 pieces of matter from distant 791 00:41:26,418 --> 00:41:30,220 stars, from distant galaxies, and we're getting them here at 792 00:41:30,222 --> 00:41:31,955 Earth and studying them. 793 00:41:33,925 --> 00:41:37,427 There are so many amazingly violent events in the universe, 794 00:41:37,429 --> 00:41:40,330 the birth of black holes, exploding stars. 795 00:41:40,332 --> 00:41:42,365 These cosmic rays that are going through your body 796 00:41:42,433 --> 00:41:45,602 right now are messengers from those events. 797 00:41:45,604 --> 00:41:47,504 In some way, you're still connected to 798 00:41:47,606 --> 00:41:49,939 those events, millions of light years away. 799 00:41:51,843 --> 00:41:54,043 These are messengers from the universe, 800 00:41:54,112 --> 00:41:56,012 telling us about how it works. 63905

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