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Research Communications

NASA'S Chandra Finds Black Holes Stirring Up Galaxies 

January 10, 2006

WASHINGTON –  Black holes are creating havoc in unsuspected places, according to a new Ohio University study of images of elliptical galaxies made by NASA's Chandra X-ray Observatory.  The discovery of far-reaching explosive activity due to giant central black holes in these old galaxies is a surprise to astronomers.

The Chandra data reveal an unsuspected turmoil in elliptical galaxies that belies their calm appearance in optical light.  Astronomers believe that massive clouds of hot gas in these galaxies have been stirred up by intermittent explosive activity from centrally located supermassive black holes.

These results come from an analysis of 56 elliptical galaxies in the Chandra data archive by Ohio University Associate Professor of Physics and Astronomy Thomas Statler and doctoral candidate Steven Diehl, who presented their data today during the annual meeting of the American Astronomical Society in Washington, D.C.
They found that, contrary to expectations, the distribution of the multimillion-degree gas in these galaxies differed markedly from that of the stars.

“Most elliptical galaxies have traditionally been considered to be quiet places, like placid lakes,” Statler said. “Our results show that these galaxies are a lot stormier than we thought.”

Previous X-ray studies have shown that elliptical galaxies contain multimillion degree gas whose mass is a few percent of that of the stars in the galaxy. Except for rare cases, violent activity in elliptical galaxies was thought to have stopped long ago. It was expected that the hot gas would have settled into an equilibrium shape similar to, but rounder than that of the stars.  However, high angular resolution imaging observations by Chandra indicate otherwise.

“We found that the distribution of hot gas has no correlation with the optical shape,” Diehl said. “Something is definitely making a mess there, and pumping energy equivalent to a supernova every century into the gas.”

Although supernovae are a possible energy source, a more probable cause has been identified. The scientists detected a correlation between the shape of the hot gas clouds and the power produced at radio wavelengths by high-energy electrons. This power output can be traced back to the centers of the galaxies, where supermassive black holes are located.

Repetitive explosive activity fueled by the infall of gas into central black holes is known to occur in giant elliptical galaxies located in galaxy clusters. Statler and Diehl’s analysis indicates that the same phenomena are occurring in isolated elliptical galaxies as well.

"These results are part of an emerging picture that shows the impact of supermassive black holes on their environment is far more pervasive than previously thought," Statler said.

Statler is director of Ohio University’s Astrophysical Institute and a member of the Structure of the Universe project, one of three major research priorities at Ohio University. The project examines areas ranging from the tiniest quarks and protons to the largest phenomenon in space.

Contacts: Andrea Gibson, Ohio University, (740) 597-2166, gibsona@ohio.edu.

Images of the elliptical galaxies may be downloaded from Chandra’s Web site: http://chandra.harvard.edu/photo/2006/galaxies/.