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The observed X-ray background is thought to result from, at the "soft" end (below 0.3 keV), Galactic X-ray emission (the "galactic" X-ray background), and, at the "hard" end (above 0.3keV), from a combination of many unresolved X-ray sources outside of the Milky Way (the "cosmic" X-ray background). The galactic X-ray background is produced largely by emission from hot gas in the Local Bubble within 100 parsecs of the Sun. Deep surveys with X-ray telescopes, such as the Chandra X-ray Observatory, have demonstrated that around 80% of the cosmic X-ray background is due to resolved extra-galactic X-ray sources, the bulk of which are unobscured ("type-1") and obscured ("type-2") active galactic nuclei (AGN). ==References== *T Shanks, I Georgantopoulos, GC Stewart, KA Pounds, "(The origin of the cosmic X-ray background )", ''Nature'' 353, 315 - 320 (26 September 1991); *Xavier Barcons, ''(The X-ray Background )'', 1992 Cambridge University Press, 324 pages ISBN 0-521-41651-5 * Audio Cain/Gay (2009) (Astronomy Cast ) X-ray Astronomy 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「X-ray background」の詳細全文を読む スポンサード リンク
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