1 00:00:00,010 --> 00:00:04,010 [Music] 2 00:00:04,030 --> 00:00:08,050 [Music] 3 00:00:08,070 --> 00:00:12,070 [Music] 4 00:00:12,090 --> 00:00:16,110 [Music] 5 00:00:16,130 --> 00:00:20,190 Narrator: The large Magellanic Cloud is among the closest galaxies to our own Milky Way, 6 00:00:20,210 --> 00:00:24,210 offering astronomers a detailed look at what makes a galaxy tick. 7 00:00:24,230 --> 00:00:28,230 One of its most striking features is the Tarantula Nebula, 8 00:00:28,250 --> 00:00:32,320 a star-forming region than any in ours or other 9 00:00:32,340 --> 00:00:36,350 neighboring galaxies. This is the source of most of the gamma rays 10 00:00:36,370 --> 00:00:40,410 we see from the LMC. Astronomers had thought the emission was a byproduct of 11 00:00:40,430 --> 00:00:44,480 star formation, which includes short-lived massive stars whose explosions 12 00:00:44,500 --> 00:00:48,510 produce shockwaves that can accelerate particles. Interactions by these 13 00:00:48,530 --> 00:00:52,530 particles, called cosmic rays, can produce gamma rays, the highest-energy 14 00:00:52,550 --> 00:00:56,620 form of light. But a discovery by NASA's Fermi Gamma-ray 15 00:00:56,640 --> 00:01:00,640 Space Telescope has turned this thinking on its head. Most of the 16 00:01:00,660 --> 00:01:04,660 emission arises from a single gamma-ray pulsar--the first ever detected in 17 00:01:04,680 --> 00:01:08,710 another galaxy. Pulsar J0540-6919 18 00:01:08,730 --> 00:01:12,790 turns out to be the most luminous gamma-ray 19 00:01:12,810 --> 00:01:16,820 pulsar yet observed, beating the previous record holder, the famous Crab 20 00:01:16,840 --> 00:01:20,870 Neubula pulsar in the Milky Way by 20 times. 21 00:01:20,890 --> 00:01:24,940 Discovered in X-rays using NASA's Einstein satellite in 1984, 22 00:01:24,960 --> 00:01:28,950 J0540 looked like a twin of the Crab until Fermi's Large Area 23 00:01:28,970 --> 00:01:33,020 Telescope unveiled its gamma-ray power. While Fermi is the most 24 00:01:33,040 --> 00:01:37,100 sensitive gamma-ray telescope ever launched, its vision is not as sharp as 25 00:01:37,120 --> 00:01:41,120 telescopes using other wavelengths. In 1998, 26 00:01:41,140 --> 00:01:47,140 NASA's RXTE satellite detected X-ray pulses from J0537-6910, 27 00:01:47,160 --> 00:01:51,180 a pulsar located just 16 arcminutes from J0540, 28 00:01:51,200 --> 00:01:55,240 or about half the apparent width of the Moon. In the early years of Fermi's 29 00:01:55,260 --> 00:01:59,280 mission, the two pulsars were seen only as a single steady gamma-ray source. 30 00:01:59,300 --> 00:02:03,360 But the vision of Fermi's Large Area Telescope 31 00:02:03,380 --> 00:02:07,400 improves over time for two reasons. First, it collects more 32 00:02:07,420 --> 00:02:11,460 gamma rays, and each one adds to the story of cosmic sources. 33 00:02:11,480 --> 00:02:15,550 Second, Fermi scientists improve their knowledge of the instrument, allowing them to 34 00:02:15,570 --> 00:02:19,560 reanalyze existing data to tease out more detail. 35 00:02:19,580 --> 00:02:23,630 Thanks to new data, and a reprocessing of old, Fermi scientists 36 00:02:23,650 --> 00:02:27,720 were finally able to detect gamma-ray pulses from J0540, 37 00:02:27,740 --> 00:02:31,760 revealing its incredible luminosity. The object is responsible for 38 00:02:31,780 --> 00:02:35,820 perhaps 60 percent of the gamma rays from the Tarantula Nebula. 39 00:02:35,840 --> 00:02:39,910 The surprise that it's the pulsar, not the nebula, suggests astronomers need to 40 00:02:39,930 --> 00:02:43,910 revisit their understanding of how cosmic rays are produced and move through 41 00:02:43,930 --> 00:02:47,980 star-forming regions. And the best way to do that, of course, is to 42 00:02:48,000 --> 00:02:52,000 keep watching the sky. 43 00:02:52,020 --> 00:02:56,040 [Beeping] 44 00:02:56,060 --> 00:03:05,899 [Beeping]