New Panorama Reveals More Than a Thousand Black Holes (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 20 Mar 2007 23:47:02 GMT
Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256/544-6535)
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
(Phone: 617/496-7998)
For Release: March 12, 2007
CXC RELEASE 03-07
New Panorama Reveals More Than a Thousand Black Holes
By casting a wide net, astronomers have captured an image of more than a
thousand supermassive black holes. 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.
The new black hole panorama was made with data from NASA's Chandra X-ray
Observatory, the Spitzer Space Telescope and ground-based optical
telescopes. The black holes in the image are hundreds of millions to
several billion times more massive than the sun and lie in the centers of
galaxies.
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.
"We're trying to get a complete census across the Universe of black holes
and their habits," said Ryan Hickox of the Harvard-Smithsonian Center for
Astrophysics (CfA) in Cambridge, Mass. "We used special tactics to hunt
down the very biggest black holes."
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 team
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.
"With this approach, we found well over a thousand of these monsters, and
have started using them to test our understanding of these powerful
objects," said co-investigator Christine Jones, also of the CfA.
The new survey raises doubts about a popular current model 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.
According to this model, astronomers would expect a large sample of black
holes to show a range of absorption of the radiation from the nuclei. This
absorption should range from completely exposed to completely obscured,
with most in-between. Nuclei that are completely obscured are not
detectable, but heavily obscured ones are.
"Instead of finding a whole range, we found nearly all of the black holes
are either naked or covered by a dense veil of gas," said Hickox. "Very
few are in between, which makes us question how well we know the
environment around these black holes."
This study found more than 600 obscured and 700 unobscured AGN, located
between about six to 11 billion light years from Earth. They were found
using an early application of a new search method. By looking at the
infrared colors of objects with Spitzer, AGN can be separated from stars
and galaxies. The Chandra and optical observations then verify these
objects are AGN. This multi-wavelength method is especially efficient at
finding obscured AGN.
"These results are very exciting, using two NASA Great Observatories to
find and understand the largest sample of supermassive black holes ever
found in the distant universe", said co-investigator Daniel Stern, of
NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The Chandra image is 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 and over 80 times larger than either of
the Chandra Deep Fields. This survey, taken in a region of the Bootes
constellation, involved 126 separate pointings of 5,000-second Chandra
exposures each. The researchers combined this with data obtained from
Spitzer, and Kitt Peak's 4-meter Mayall and the MMT 6.5-meter optical
telescopes, both located outside Tuscon, Ariz., from the same patch of
sky.
NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra
program for the agency's Science Mission Directorate. The Smithsonian
Astrophysical Observatory controls science and flight operations from the
Chandra X-ray Center, Cambridge, Mass.
Additional information and images are available at:
http://chandra.harvard.edu/photo/2007/bootes/
and
http://chandra.nasa.gov
.
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