Contact: June Malone
Media Relations Department
(256) 544-0034

RELEASE: 00-166

NASA’s Chandra X-ray Observatory has examined the stormy
environs of a giant black hole in the active galaxy NGC 3783 and
measured the dramatic effects of intense radiation produced by
matter before it plunges into the black hole. This radiation heats
surrounding gas and drives a million mile per hour wind away from
the crushing grip of the black hole’s gravity.

A team of researchers used the High Energy Transmission Grating
in combination with the CCD X-ray camera aboard Chandra to
study the properties of the wind. “X-ray observations allow
astronomers to probe these extremely powerful gas flows that have
been suspected to exist, but have been impossible to study
precisely before,” said Professor Niel Brandt, of Pennsylvania State
University, University Park, one of the leaders of the team.

The grating spreads the incident X-ray beam into a rainbow-like
display of hundreds of different X-ray “colors” or energies.
Computers translated this display into a jagged-line plot that
resembles an electrocardiogram. Specific elements reveal their
presence by sharp absorption dips in the plot. By examining the
widths and locations of these dips, the researchers can use the
same principle used by a radar gun to measure velocities in the
extreme environment of the galaxy’s core.

“This is the most detailed X-ray spectrum ever taken of a galaxy
with an active black hole,” said Dr. Shai Kaspi, also of Penn State.
“It reveals that the wind contains oxygen, neon, magnesium, silicon,
sulfur, argon, and iron.” An analysis of the wind by team member
Professor Hagai Netzer of Tel-Aviv University in Israel, showed that
the wind almost completely surrounds the black hole.

The event horizon of the central black hole in NGC 3783 has a
diameter about a hundred times that of the sun, but it produces
more radiation than a billion suns as gas is sucked into the black
hole at nearly the speed of light. A portion of this powerful radiation
is absorbed by gas that surrounds the black hole. Electrons in the
gas are boosted from low to high-energy states, and some are
ripped from their atoms. The gas is heated to a hundred thousand
degrees Celsius or more and driven away from the black hole into
the galaxy.

The research team for this investigation also includes Dr. Rita
Sambruna, Dr. George Chartas, Professor Gordon Garmire, and
Professor John Nousek of Penn State. The High Energy
Transmission Grating Spectrometer was built by the
Massachusetts Institute of Technology (MIT), Cambridge, Mass.
The Advanced CCD X-ray Spectrometer (ACIS) X-ray camera was
developed for NASA by Penn State and MIT.

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages
the Chandra program. TRW, Inc., Redondo Beach, Calif., is the
prime contractor for the spacecraft. The Smithsonian’s Chandra
X-ray Center controls science and flight operations from
Cambridge, Mass.

Images associated with this release are available on the Web at: and and

Science Contacts:
Niel Brandt, 814-865-3509,
Shai Kaspi, 814-863-1756,