Local Star Factory Produces Some of the Most Powerful X rays in the Universe
Contact:
Christopher Wanjek
wanjek@gsfc.nasa.gov
301-286-4453June 6, 2001
Pasadena, Calif. -- Near the rowdy core of the Milky Way galaxy, where stars shine so brightly and plentifully that planets there would never experience nighttime, astronomers have discovered a wholly new phenomenon: a cluster of young stars immersed in a cauldron of 60-million-degree gas.
Prof. Farhad Zadeh of Northwestern University and his collaborators used NASA's Chandra X-ray Observatory to trace the flow of X-ray-emitting gas around the brilliant Arches cluster, a well-studied star-forming region that is home to some of our Galaxy's largest and youngest stars. They found that the sheer concentration of massive stars here produces fierce stellar winds that slam into each other and generate a diffuse halo of X rays of an unexpected ferocity.
"We have never seen such a phenomenon," said Zadeh in a press conference today at the American Astronomical Society meeting in Pasadena, Calif. "The gas in the star cluster becomes so energetic that it flies out of the strong gravitational confines of the cluster all together, perhaps to seed star birth elsewhere. This is remarkable because we are confirming theoretical predictions that stellar winds from massive stars can collide with each other and generate hot gas."
Massive stars, newborn stars, and stellar winds have long been known to emit X-rays. The Chandra results are significant because they identify a new type of mechanism to generate X rays as energetic as those seen in distant starburst galaxies, which are known for their furious pace of star production.
The Arches cluster is about 25,000 light years from Earth and only about 1 to 2 million years old. It is also less than 100 light years from what is thought to be a supermassive black hole in the center of our Galaxy. The cluster contains 150 hot and young stars, known as O stars, concentrated within a distance of one light year, making it the most compact cluster known in the Milky Way galaxy. In comparison, humans would need to travel over 4 light years from the Sun to reach the next closest star.
Many of the stars in the Arches cluster are more than 20 times as massive as the Sun and live short, furious lives lasting only a few million years ending with a supernova explosion. Much of the bulk in these stars explodes into space, enriching the medium between stars with heavy elements and creating of a new generation of stars.
The region in and around the Arches cluster is a microcosm of what is likely occurring in starburst galaxies. Thus, scientists have a perfect "local" laboratory to study the structure and evolution of young stars, since all the stars are located in a small volume at the same distance from us and are born at the same time.
"The Arches cluster is one of the best local analogues of the more massive starburst galaxies, which are likely the most prodigious stellar nurseries seen anywhere," said Casey Law of Harvard-Smithsonian Center for Astrophysics. "Yet the Arches cluster is in our backyard, not millions of light years away like starburst galaxies."
The Chandra observation also suggests that gas leaked from the Arches clusters and others like it may contribute to mysterious diffuse hot gas found around the center of the Milky Way.
"Chandra is helping us understand the 'energy budget' around the Arches cluster and the galaxy core," said Cornelia Lang of the University of Massachusetts. "We now see that the stars in the Arches cluster are powerful enough to account for the heating of the so-called 'Arched Filament' clouds, which encircle the cluster and extend for more than 75 light years."
Zadeh and collaborators intend to search for X-ray emission from other clusters of stars near the Galactic center and compare this to newer, longer Chandra observations of the Arches cluster.
Chandra observed Arches cluster region for 51,000 seconds with its Advanced CCD Imaging Spectrometer (ACIS). In addition to Drs. Law and Lang, the research team for this investigation included Antonella Fruscione from the Harvard-Smithsonian Center for Astrophysics; Daniel Wang from University of Massachusetts; Mark Wardle of the University of Sydney, Australia; and Angela Cotera from University of Arizona.
The 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 World Wide Web at:
http://chandra.harvard.edu/press/01_releases/press_060601.html and
http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-200.html.-30-