RELEASE: 00-182

NASA’s Chandra X-ray Observatory image of Perseus A, a supergiant
galaxy in the center of a galaxy cluster, provides new insight into how the
galaxy has grown by cannibalizing gas and other galaxies in the vicinity.
For the first time astronomers see an X-ray shadow cast by a smaller galaxy
as its gas is being stripped away by the enormous central galaxy.

The research was reported by Professor Andrew Fabian of the
Institute of Astronomy, Cambridge, England on June 7 at the 196th national
meeting of the American Astronomical Society in Rochester, N.Y. Other
members of the research team are Jeremy Sanders, Stefano Ettori, Steve
Allen, Carolin Crawford, Kazushi Iwasawa and Roderick Johnstone of the
Institute of Astronomy; Gregory Taylor of the National Radio Astronomy
Observatory, Socorro, N.M.; and Patrick Ogle of the Massachusetts Institute
of Technology, Cambridge.

Perseus A, or NGC 1275, is in the center of a large galaxy cluster
320 million light years from Earth. The cluster, which contains thousands
of galaxies and enough gas to make thousands more, is one of the largest
gravitationally bound objects in the universe. Over the eons, Perseus A has
accumulated hundreds of billions of stars to become one of the most massive
known galaxies as gas and galaxies have been pulled inward by gravity.

The Chandra image shows a region of hot gas that extends over
several hundred thousand light years. The gas in the outer portion of the
cluster has a temperature of 70 million degrees. The cluster gas cools
gradually and settles toward the center of the cluster. A galaxy with
“only” about 20 billion stars is falling into Perseus A (located at two
o’clock from the center of the image) and shows up as a small dark patch due
to absorption of X-rays by cool gas in the infalling galaxy.

Another larger hole further out is thought to be due to a bubble of
high energy particles ejected in an explosion from Perseus A hundreds of
millions of years ago. These outbursts are presumably fueled by matter
releasing tremendous quantities of energy as it falls into a giant black
hole in the center, or nucleus of the galaxy.

Closer in, the effects of a more recent explosion show up as dark
twin cavities, each large enough to contain a galaxy half the diameter of
our Milky Way galaxy. These cavities, which have been detected at lower
resolution by previous X-ray satellites, appear to be buoyant, magnetized
bubbles of energetic particles. The Chandra image shows that the gas that
has piled up in the brilliant rims has “cooled” to a temperature of 30
million degrees. A long spiral of hot gas appears to be winding inward
around the cavities toward the center of the galaxy. Fabian and his
colleagues propose that the cooling of gas in this spiral can lead to the
formation of a spiral structure of stars that has been detected in optical
images of the galaxy.

The observation was made on January 29, 2000 for 6.8 hours using the
Advanced CCD Imaging Spectrometer (ACIS).

The Advanced CCD X-ray Spectrometer (ACIS) X-ray camera was
developed for NASA by Pennsylvania State University, University Park, and
Massachusetts Institute of Technology, Cambridge. 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 World Wide
Web at
http://chandra.harvard.edu and http://chandra.nasa.gov