费米望远镜首次在外星系发现伽马射线

Researchers using NASA's Fermi Gamma-ray Space Telescope have discovered the first gamma-ray pulsar in a galaxy¹ other than our own. The object sets a new record for the most luminous² gamma-ray pulsar known. The pulsar lies in the outskirts³ of the Tarantula Nebula⁴ in the Large Magellanic Cloud, a small galaxy that orbits our Milky⁵ Way and is located 163,000 light-years away. The Tarantula Nebula is the largest, most active and most complex star-formation region in our galactic neighborhood. It was identified as a bright source of gamma rays, the highest-energy form of light, early in the Fermi mission. Astronomers⁶ initially⁷ attributed this glow to collisions of subatomic particles accelerated in the shock waves produced by supernova explosions. 

 

"It's now clear that a single pulsar, PSR J0540-6919, is responsible for roughly half of the gamma-ray brightness we originally thought came from the nebula," said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research (CNRS) and the Research Institute in Astrophysics and Planetology in Toulouse, France. "That is a genuine surprise."

 

When a massive star explodes as a supernova, the star's core may survive as a neutron⁸ star, where the mass of half a million Earths is crushed into a magnetized ball no larger than Washington, D.C. A young isolated⁹ neutron star spins tens of times each second, and its rapidly spinning magnetic field powers beams of radio waves, visible light, X-rays and gamma rays. If the beams sweep past Earth, astronomers observe a regular pulse of emission¹⁰ and the object is classified as a pulsar.

 

The Tarantula Nebula was known to host two pulsars, PSR J0540-6919 (J0540 for short) and PSR J0537?6910 (J0537), which were discovered with the help of NASA's Einstein and Rossi X-ray Timing¹¹ Explorer (RXTE) satellites, respectively. J0540 spins just under 20 times a second, while J0537 whirls at nearly 62 times a second -- the fastest-known rotation¹² period for a young pulsar.

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