RELEASE: 00-179

NASA’s Chandra X-ray Observatory has shown that a giant gas cloud is
being blasted by X-rays from the vicinity of a giant black hole which lurks
in its center. The observation is of special interest because it shows the
disruptive effects that a massive black hole can have over thousands of
light years.

The results are being presented today by Drs. Patrick M. Ogle,
Herman L. Marshall, Julia C. Lee, and Claude Canizares of the Massachusetts
Institute of Technology (MIT), Cambridge, at the 196th national meeting of
the American Astronomical Society in Rochester, N.Y. The observation also
demonstrates that the searchlight beam of X-rays from the black hole can be
used to probe the environment around a black hole.

The galaxy NGC 4151 is located at a distance of 50 million light
years in a direction just south of the Big Dipper. It is a prominent
example of a class of galaxies that show unusual energetic activity in their
nucleus. This activity is now known to be due to the presence of a giant
black hole in the nucleus with an estimated mass 10 million times that of
the sun. As matter swirls toward the black hole, it releases a prodigious
amount of energy, much of it in X-rays. Previous observations showed that
X-rays are also coming from an enormous cloud 3000 light years across that
surrounds the black hole.

The precise mirrors of Chandra allowed astronomers to make an X-ray
image showing unprecedented detail of the massive cloud in the center of NGC
4151. The brightest regions in the cloud correspond to wisps that were
previously observed in visible light by the Hubble Space Telescope. The
shape of the cloud confirms that X-rays from the black hole are collimated
into a narrow beam, and illuminate only certain quadrants of the galaxy.

“The black hole is shining an X-ray searchlight which illuminates
the clouds in the night sky of NGC 4151” said Ogle.

By using the High Energy Transmission Grating (HETG), astronomers
were able to resolve the X-ray spectrum from the nebula surrounding the
black hole into emission from its constituent elements. It was found that
the gas cloud contains nitrogen, oxygen, neon, magnesium, aluminum, silicon
and iron. However, the atoms of these elements have been stripped of most of
their electrons by energetic X-rays coming from the center of NGC 4151.
This provides direct evidence that the cloud is powered by the giant black
hole which resides there. “The cloud is being thoroughly cooked by the
powerful beam from the black hole,” said Ogle.

In addition, the Chandra HETG spectrum reveals that portions of the
cloud are moving away from us at a velocity of 800,000 mph. “We’re probably
seeing gas that is being blown away from the far side of the black hole by
the pressure of the radiation from the black hole,” Ogle said.

Chandra data were taken with the HETG in conjunction with the
Advanced CCD Imaging Spectrometer (ACIS) on March 5-6, 2000. HETG was built
by MIT and ACIS was built by Pennsylvania State University, University Park,
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.

High resolution digital versions of the X-ray image (JPG, 300 dpi
TIFF ) and other information associated with this release are available on
the Internet at: and

Further information on the HETG may be found at:

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Steve Roy

Media RelationsDepartment

(256) 544-0034

Deborah Halber


Cambridge, MA

(617) 258-9276

Dr. Wallace Tucker

Chandra X-ray Observatory Center

Cambridge, MA

(617) 496-7998


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