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April
12, 2007: NASA's Chandra X-ray Observatory has observed
a remarkable eclipse of a supermassive black hole, allowing
a disk of hot matter swirling around the hole to be measured
for the first time.
 The
supermassive black hole is located in NGC 1365, a spiral galaxy
60 million light years from Earth. It contains a so-called
active galactic nucleus, or AGN. Scientists believe that a
black hole at the center of the AGN is fed a steady stream
of material from a surrounding disk. Matter just about to
fall into a black hole should be heated to millions of degrees
before passing over the event horizon, or point of no return.
This super-heated disk material glows brightly in the X-ray
part of the electromagnetic spectrum where Chandra can see
it.
Right:
The black hole eclipse occurred in the core of this barred
spiral galaxy, NGC 1365. [More]
The
disk of gas around the central black hole in NGC 1365 is much
too small to resolve directly with a telescope. However, the
disk was eclipsed by an intervening cloud. By recording the
time taken for the disk to go in and out of eclipse, scientists
were able to estimate the diameter of the disk.
"For years
we've been struggling to confirm the size of this X-ray structure,"
said Guido Risaliti of the Harvard-Smithsonian Center for
Astrophysics (CfA) in Cambridge, Mass, and the Italian Institute
of Astronomy (INAF). "A serendipitous eclipse enabled
us to make this breakthrough."
The
Chandra team directly measured the diameter of the X-ray source
as about seven times the distance between the Sun and the
Earth or 7 AU (astronomical units). For comparison, if such
a disk were placed in our own solar system, it would swallow
all the planets out to Mars and most of the asteroid belt
as well.
Above:
An artist's concept (not to scale) of Chandra observing the
black hole eclipse. [More]
According
to these measurements, the source of X-rays is about 2 billion
times smaller than the host galaxy NGC 1365 and only about
10 times larger than the estimated size of the black hole's
event horizon. This is consistent with theoretical predictions.
"Thanks to
this eclipse, we were able to probe much closer to the edge
of this black hole than anyone has been able to before,"
said co-author Martin Elvis from CfA. "Material this
close in will likely cross the event horizon and disappear
from the universe in about a hundred years, a blink of an
eye in cosmic terms."
In
addition to measuring the size of this disk of material, Risaliti
and his colleagues were also able to estimate the location
of the dense gas cloud that eclipsed the X-ray source and
central black hole. The Chandra data show that this cloud
is one hundredth of a light year from the black hole's event
horizon--much closer than anyone expected. So this is a bit
of a puzzle.
"AGN
[are among] the brightest objects in the cosmos and they are
powerful probes of the early history of the Universe. It's
vital we understand their basic structure," said Risaliti.
"It turns out that we still have work to do to understand
these monsters."
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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.
Source: NASA Press Release
| Editor:
Dr. Tony Phillips | Credit: Science@NASA
|
