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[Music]

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Narrator: The large Magellanic Cloud is among the closest galaxies to our own Milky Way,

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offering astronomers a detailed look at what makes a galaxy tick.

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One of its most striking features is the Tarantula Nebula,

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a star-forming region than any in ours or other

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neighboring galaxies. This is the source of most of the gamma rays

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we see from the LMC. Astronomers had thought the emission was a byproduct of

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star formation, which includes short-lived massive stars whose explosions

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produce shockwaves that can accelerate particles. Interactions by these

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particles, called cosmic rays, can produce gamma rays, the highest-energy

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form of light. But a discovery by NASA's Fermi Gamma-ray

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Space Telescope has turned this thinking on its head. Most of the

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emission arises from a single gamma-ray pulsar--the first ever detected in

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another galaxy. Pulsar J0540-6919

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turns out to be the most luminous gamma-ray

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pulsar yet observed, beating the previous record holder, the famous Crab

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Neubula pulsar in the Milky Way by 20 times.

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Discovered in X-rays using NASA's Einstein satellite in 1984,

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J0540 looked like a twin of the Crab until Fermi's Large Area

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Telescope unveiled its gamma-ray power. While Fermi is the most

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sensitive gamma-ray telescope ever launched, its vision is not as sharp as

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telescopes using other wavelengths. In 1998,

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NASA's RXTE satellite detected X-ray pulses from J0537-6910,

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a pulsar located just 16 arcminutes from J0540,

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or about half the apparent width of the Moon. In the early years of Fermi's

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mission, the two pulsars were seen only as a single steady gamma-ray source.

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But the vision of Fermi's Large Area Telescope

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improves over time for two reasons. First, it collects more

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gamma rays, and each one adds to the story of cosmic sources.

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Second, Fermi scientists improve their knowledge of the instrument, allowing them to

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reanalyze existing data to tease out more detail.

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Thanks to new data, and a reprocessing of old, Fermi scientists

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were finally able to detect gamma-ray pulses from J0540,

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revealing its incredible luminosity. The object is responsible for

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perhaps 60 percent of the gamma rays from the Tarantula Nebula.

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The surprise that it's the pulsar, not the nebula, suggests astronomers need to

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revisit their understanding of how cosmic rays are produced and move through

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star-forming regions. And the best way to do that, of course, is to

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keep watching the sky.