1 00:00:00,020 --> 00:00:04,020 [Music] 2 00:00:04,040 --> 00:00:08,070 [Music] 3 00:00:08,090 --> 00:00:12,120 [Music] 4 00:00:12,140 --> 00:00:16,180 [Music] 5 00:00:16,200 --> 00:00:20,220 Narrator: Parkes 1441+25 is a distant 6 00:00:20,240 --> 00:00:24,270 galaxy powered by a supermassive black hole. It's so far away 7 00:00:24,290 --> 00:00:28,290 its light takes more than half the current age of the universe to reach us. 8 00:00:28,310 --> 00:00:32,370 This is NASA's Fermi Gamma-ray Space Telescope, 9 00:00:32,390 --> 00:00:36,450 our sharpest satellite eyes on the gamma-ray sky. But Fermi's 10 00:00:36,470 --> 00:00:40,510 effective collecting area is about the size of two office desks. It can't 11 00:00:40,530 --> 00:00:44,540 catch everything. Ground-based gamma-ray observatories sport 12 00:00:44,560 --> 00:00:48,570 much larger light collectors than Fermi, but like traditional telescopes, they 13 00:00:48,590 --> 00:00:52,590 only work at night. Both MAGIC and VERITAS work 14 00:00:52,610 --> 00:00:56,650 by catching faint flashes of visible light produced when a high-energy 15 00:00:56,670 --> 00:01:00,700 gamma ray strikes the upper atmosphere. This creates a shower 16 00:01:00,720 --> 00:01:04,740 of fast-moving charged particles that emit a glow called Cerenkov radiation. 17 00:01:04,760 --> 00:01:08,760 On April 16, 2015, 18 00:01:08,780 --> 00:01:12,810 Parkes 1441 was exhibiting high activity across all wavelengths. 19 00:01:12,830 --> 00:01:16,830 Scientists looking at Fermi data reported a strong gamma-ray 20 00:01:16,850 --> 00:01:20,840 outburst. Based on this alert, scientists on the MAGIC team began 21 00:01:20,860 --> 00:01:24,890 monitoring the galaxy and detected very-high-energy gamma rays. 22 00:01:24,910 --> 00:01:28,960 That was the cue for VERITAS to take a look, and it also captured the 23 00:01:28,980 --> 00:01:32,990 quasar's very-high-energy emission. These detections were 24 00:01:33,010 --> 00:01:37,020 remarkable because high-energy light usually can't travel extreme distances 25 00:01:37,040 --> 00:01:41,070 These gamma rays had been traveling for half the age of the cosmos 26 00:01:41,090 --> 00:01:45,120 passing through all the light emitted by stars, supernovae, and everything else 27 00:01:45,140 --> 00:01:49,140 that flashed and glowed across more than 7 billion years of cosmic history. 28 00:01:49,160 --> 00:01:53,170 Astronomers call this remnant glow is called the extragalactic background light 29 00:01:53,190 --> 00:01:57,210 background light. When a gamma ray strikes this lower-energy light, it converts into 30 00:01:57,230 --> 00:02:01,230 a pair of particles, an electron and a positron. The farther 31 00:02:01,250 --> 00:02:05,270 gamma rays travel the more likely it is they'll undergo this process, which effectively 32 00:02:05,290 --> 00:02:09,300 erases the gamma rays from the universe before we have the opportunity to detect 33 00:02:09,320 --> 00:02:13,370 them. Parkes 1441 is one of the most 34 00:02:13,390 --> 00:02:17,450 distant sources of gamma rays with energies above 100 GeV, 35 00:02:17,470 --> 00:02:21,490 tens of billions of times the energy in visible light. That the light 36 00:02:21,510 --> 00:02:25,530 reached us at all provides information about the extragalactic background light 37 00:02:25,550 --> 00:02:29,580 when the universe was half its present age. Those gamma rays 38 00:02:29,600 --> 00:02:33,730 originated from the particle jet produced by the galaxy's supermassive black hole. 39 00:02:33,750 --> 00:02:37,890 Astronomers think they started their journey only about 5 light-years from the 40 00:02:37,910 --> 00:02:41,960 black hole. Escaping the galaxy's crowded central regions 41 00:02:41,980 --> 00:02:46,050 means this high-energy light never interacted with matter or starlight, collisions 42 00:02:46,070 --> 00:02:50,120 that would have doomed them to convert into particles. This is one reason 43 00:02:50,140 --> 00:02:54,180 why extremely energetic gamma rays are few and far between, and why astronomers 44 00:02:54,200 --> 00:02:58,250 prize the relatively few photons they can find. 45 00:02:58,270 --> 00:03:02,270 The story of gamma rays from Parkes 1441 isn't a mere tale of survival. 46 00:03:02,290 --> 00:03:06,340 These photons executed a jailbreak of cosmic proportions, 47 00:03:06,360 --> 00:03:10,370 and it took Fermi, MAGIC, and VERTIAS to round them up. 48 00:03:10,390 --> 00:03:14,380 [Beeping] 49 00:03:14,400 --> 00:03:18,400 [Beeping] 50 00:03:18,420 --> 00:03:24,918 [Beeping]