"THE X-RAY BACKGROUND - A YEAR OF DISCOVERY"
The x-ray background had been one of the oldest unsolved
problems in
astrophysics. Discovered in the first detection of non-solar
x-rays in a
rocket flight in 1962 the nature of the sources that
produce the x-ray
background were basically unknown. With the first results
from Chandra and
XMM, powerful new x-ray telescopes launched in 1999,
we have "resolved"
out almost all of the x-ray background into point sources.
While many of
these are too faint to obtain optical redshifts for and
some are invisible
even to the Keck telescope, our group has been able to
identify ~1/2 of
the objects. These form a heterogeneous class of "normal"
broad line AGN,
objects with "non-normal" galaxy spectra and, apparently,
normal galaxies.
We believe that the fundamental sources are all the same,
massive black
holes in the centers of galaxies. With reasonable assumptions
we find that
the x-ray background source counts and the redshift distribution
of the
sources is consistent with almost every massive black
hole in the universe
being at some time a luminous x-ray source.