January 14, 2000
Consider this: the iron in your blood was forged in a supernova explosion billions of years ago.
Chandra Resolves the Hard X-Ray Background
Birthday · January 14, 2000
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APOD published January 14, 2000. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
It is everywhere but nobody knew why. In every direction at all times, the sky glows in X-rays. The X-ray background phenomenon was discovered over 35 years ago, soon after the first X-ray satellites were launched, and has since gone unexplained. Yesterday results were released using data from the recently launched Chandra X-Ray Observatory that appears to have resolved much of this mystery. The above photograph shows that about 80 percent of the apparently diffuse hard X-ray background can be resolved into very many very faint sources. The new question is now what are these sources? Early speculation, much of which predates these observations, holds that many of these sources are the active centers of distant galaxies, probably involving massive black holes. Still other sources may be of origins currently unknown.