cosmic X-ray background (CXB)
An X-ray and gamma-ray
glow that comes from all parts of the sky. First revealed in the 1970s by
early X-ray satellites, its origin proved something of a mystery. Beginning
in 2000, however, more powerful orbiting X-ray instruments, such as the
XMM-Newton Observatory, have resolved
some of this enigmatic background into many faint individual sources, their
X-ray characteristics pointing to huge amounts of material falling into
supermassive black holes
in very distant galaxies. These results add to the growing consensus that
massive black holes hold court at the center of all large galaxies and that,
from across the universe, X-rays produced as matter feeds these black holes
account for the bulk of the CXB.
|X-ray image of the sky taken through the Lockman
hole by the XMM-Newton Observatory,
resolving some of the background into many faint individual sources.
The image is color-coded, with red representing relatively low energy
X-rays, photons with 500 or so times the energy of visible light.
Green and blue colors correspond to increasingly energetic X-rays
with up to about 10,000 times visible light energies. Notably, the
faint sources tend to be green and blue, showing X-ray characteristics
of huge amounts of material falling into supermassive black holes
in very distant galaxies. Credit: G. Hasinger (AIP) et al., XMM-Newton,
The CXB is one of several components of the cosmic