Press Release

X-ray Arcs Tell The Tale of Giant Eruption

By SpaceRef Editor
August 7, 2002
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Long ago, a giant eruption occurred in a nearby galaxy and plunged it
into turmoil. Now NASA’s Chandra X-ray Observatory has revealed the
remains of that explosion in the form of two enormous arcs of hot gas.
This discovery can help astronomers better understand the cause and
effect of violent outbursts from the vicinity of supermassive black
holes in the centers of many so-called “active” galaxies.

Scientists from the Harvard-Smithsonian Center for Astrophysics (CfA)
report that two arc-like structures of multimillion-degree gas in the
galaxy Centaurus A appear to be part of a ring 25,000 light years in
diameter. The size and location of the ring suggest that it could have
been produced in a titanic explosion that occurred about ten million
years ago.

A composite image of the galaxy made with radio (red and green), optical
(yellow-orange), and X-ray data (blue) presents a stunning tableau of a
tumultuous galaxy. A broad band of dust and cold gas is bisected at an
angle by opposing jets of high-energy particles blasting away from the
supermassive black hole in the nucleus. Lying in a plane perpendicular
to the jets are the two large arcs of X-ray emitting hot gas.

“Putting all the images together was the key to understanding what
Chandra showed,” said Margarita Karovska, lead author on a paper in the
September 6, 2002, issue of The Astrophysical Journal. “Suddenly it all
clicked in, as with a giant puzzle, and the images fit together to make
a complete picture of the galaxy geometry that was not at all apparent

The team proposes that the orientation of the arcs of hot gas
perpendicular to the jet and the symmetry of the projected ring with
respect to the center of the galaxy could be evidence that the ring is
the result of a giant eruption in the nucleus of the galaxy 10 million
years ago. This explosion may have produced a galaxy-sized shock wave
that has been moving outward at speeds of a million miles per hour. The
age of 10 million years for the outburst is consistent with other
optical and infrared observations that indicate that the rate of star
formation in the galaxy increased dramatically at about that time.

Other authors have suggested that the merger of a small spiral galaxy
with Centaurus A about a hundred million years ago triggered the
high-energy jets and the ongoing violent activity in the nucleus of the
galaxy. The tremendous energy released when a galaxy is “turned on” by
a collision can have a profound influence on the subsequent evolution of
the galaxy and its neighbors. The mass of the central black hole can
increase, the gas reservoir for the next generation of stars can be
expelled, and the space between the galaxies can be enriched with
heavier elements.

“Active galaxies could have played a significant role in the evolution
of galaxies in the early universe when collisions between galaxies were
much more frequent,” said Giuseppina Fabbiano, a coauthor on the paper.
“Centaurus A, at a distance of only 11 million light years, gives us a
rare opportunity to study such an active galaxy in action.”

Chandra observed Centaurus A with its High Resolution Camera instrument
on September 10, 1999, for approximately 4.7 hours. Other members of
CfA research team include Martin Elvis, Ralph Kraft, Stephen Murray, and
Fabrizio Nicastro

The HRC was built by the Smithsonian Astrophysical Observatory in
Cambridge, Mass. NASA’s Marshall Space Flight Center, Huntsville, AL,
manages the Chandra program for the Office of Space Science, Washington,
DC. TRW, Inc., Redondo Beach, California, is the prime contractor for
the spacecraft. The Smithsonian’s Chandra X-ray Center controls science
and flight operations from Cambridge, MA.

Images associated with this release are available



Science Contact
Margarita Karovska,, 617-495-7347

SpaceRef staff editor.