HEAPOW: Background Check (2010 Mar 15)
NASA's Fermi Probes "Dragons" of the Gamma-ray SkyMost astronomers find backgrounds annoying. Background emission contaminates everything, and before emission from a source can be characterized, contaminating background emission needs to be estimated and subtracted away. But what causes the background, anyway? There are many possible sources - for example the microwave background is produced by the Big Bang. At higher energies the source of the background emission is less clear. Astronomers have known for years that an apparently diffuse glow of gamma-rays permeates the entire universe. As gamma-ray detector technology has improved, some of this emission has become resolved into unique sources. But even at the spatial resolution of the Fermi Gamma-Ray Observatory, the best all-sky gamma-ray monitor ever flown, the gamma-ray background persists, unresolved and unapologetic. A new analysis of the gamma-ray background seen by the Fermi observatory has surprised astronomers. The most widely-held belief is that the gamma-ray background is due to emission from supermassive black holes actively feeding at the center of galaxies. But as the plot above shows, analysis of Fermi data suggests that such emission only makes up about 10-20% of the gamma ray background. What makes up the rest? Stay tuned.
http://asterisk.apod.com/vie ... 31&t=18569
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