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NASA | A Flickering X-ray Candle

The Crab Nebula, created by a supernova seen nearly a thousand years ago, is one of the sky's most famous "star wrecks." For decades, most astronomers have regarded it as the steadiest beacon at X-ray energies, but data from orbiting observatories show unexpected variations, showing astronomers their hard X-ray "standard candle" isn't as steady as they once thought. From 1999 to 2008, the Crab brightened and faded by as much as 3.5 percent a year, and since 2008, it has faded by 7 percent. The Gamma-ray Burst Monitor on NASA's Fermi satellite first detected the decline, and Fermi's Large Area Telescope also spotted two gamma-ray flares at even higher energies. Scientists think the X-rays reveal processes deep within the nebula, in a region powered by a rapidly spinning neutron star -- the core of the star that blew up. But figuring out exactly where the Crab's X-rays are changing over the long term will require a new generation of X-ray telescopes. This video is public domain and can be downloaded at: http://svs.gsfc.nasa.gov/goto?10708 Like our videos? Subscribe to NASA's Goddard Shorts HD podcast: http://svs.gsfc.nasa.gov/vis/iTunes/f0004_index.html Or find NASA Goddard Space Flight Center on facebook: http://www.facebook.com/NASA.GSFC Or find us on Twitter: http://twitter.com/NASAGoddard
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