New Panorama Reveals More Than a Thousand Black Holes

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.

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.

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 obscured AGN.

Fast Facts for Bootes Field:

Credit          X-ray: NASA/CXC/CfA/R.Hickox et al.; Moon: NASA/JPL
Scale   Chandra image is 148 by 198 arcmin
Category        Quasars & Active Galaxies, Cosmology/Deep Fields/X-ray
Coordinates (J2000)     RA 14h 32m 00.00s | Dec +34º 06′ 00.00″
Constellation   Boötes
Observation Dates       126 pointings between March – April 2003
Observation Time        175 hours
Obs. IDs        3596-3660, 4218-4282
Color Code      Red(0.5-1.3 keV); Blue(1.3-2.5 keV); Green(2.5-7 keV)
Instrument      ACIS
References      Hickox et al. (2007), ApJ, submitted
Distance Estimate       A range from 1 billion to 11 billion light years
Release Date    March 12, 2007

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