A new wide-field panorama reveals more than a thousand
supermassive black holes in the centers of galaxies, some up to
several billion times more massive than the sun. This survey,
taken in a region of the Bootes constellation, involved 126
separate Chandra exposures of 5,000-seconds each, making it the
largest contiguous field ever obtained by the observatory. At
9.3 square degrees, it is over 40 times larger than the full
moon seen on the night sky, which is also shown in this graphic
for scale. In this image, the red represents low-energy X-rays,
green shows the medium range, and blue the higher energy X-rays.
Credit: X-ray: NASA/CXC/CfA/R.Hickox et al.; Moon: NASA/JPL
Material falling into these black holes at high rates generates
huge amounts of light that can be detected in different
wavelengths. These systems are known as active galactic nuclei,
or AGN. When combined with data from the Spitzer Space Telescope
and Kitt Peak's 4-meter Mayall and the MMT 6.5-meter optical
telescopes, these results give astronomers a snapshot of a
crucial period when these monster black holes are growing, and
provide insight into the environments in which they occur.
Instead of staring at one relatively small part of the sky for a
long time, as with the Chandra Deep Fields -- two of the longest
exposures obtained with the observatory -- and other
concentrated surveys, this strategy employed a technique that
scanned a much bigger portion with shorter exposures. Since the
biggest black holes power the brightest AGN, they can be spotted
at vast distances, even with short exposures.
Black hole not enshrouded by this ring of material, and,
therefore, emits X-ray, infrared, and optical (green) radiation.
Credit: X-ray: NASA/CXC/CfA/R.Hickox et al.; Infrared:
NASA/JPL/Caltech/P.Eisenhardt & D.Stern et al.; Optical: NOAO/B.Jannuzi
& A.Dey et al.
The survey gives a new test of a popular model for AGN in which
a supermassive black hole is surrounded by a doughnut-shaped
region, or torus, of gas. An observer from Earth would have
their view blocked by this torus by different amounts, depending
on the orientation of the torus, so some of the nuclei will be
obscured and some won't. This study identified more than 600
obscured and 700 unobscured AGN, located between about six to 11
billion light years from Earth. The red sources are mostly
unobscured AGN and the green and blue sources are dominated by
Written from a news release by Chandra