G21.5-0.9: A supernova remnant in the constellation Scutum			20/09/1999
			Images from NASA's Chandra X-ray Observatory reveal previously unobserved features in the remnants of supernova explosions. Remnant G21.5-0.9 shows dramatic new details of the prodigious production of energetic particles by a rapidly rotating, highly magnetized neutron star, as well as the enormous shell structures produced by the explosions.
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Image Credit: NASA/CXC/SAO.
The identification of G21.5-0.9 as the remnant of a supernova explosion is based on indirect evidence from radio and x-ray observations. At both radio and x-ray wavelengths, it appears as round patch in the sky. Detailed observations with radio telescopes confirm that the radio waves are produced by high energy electrons spiraling around magnetic field lines (synchrotron radiation). The x-rays are probably produced by the same process, but the electrons involved have energies many thousands times higher than those that produce the radio waves. The favored theory is that the high energy electrons responsible for both the radio and x-ray emission are produced by a rapidly rotating, highly magnetized neutron star left behind when a massive star exploded some 40,000 years ago.		Constellation: Scutum
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