Dolores Beasley, Steve Roy, Megan Watzke

Near the crowded core of the Milky Way galaxy, where stars

are so plentiful and shine so brightly that planets there would

never experience nighttime, astronomers have found a new

phenomenon: a cauldron of 60-million degree gas enveloping a

cluster of young stars.

Professor Farhad Zadeh of Northwestern University, Evanston, IL,

and his collaborators used NASA’s Chandra X-ray Observatory to

trace the gas around the Arches cluster, a well-studied region

of star formation that is home to some of our galaxy’s largest

and youngest stars.

“This is the first time we have seen a young cluster of stars

surrounded by such a halo of high-energy X-rays,” said Zadeh in

a news conference at the American Astronomical Society in

Pasadena, CA. “This supports theoretical predictions that

stellar winds from massive stars can collide with each other and

generate very 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 this new mechanism of stellar winds

colliding 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 one-to-two 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,

young stars, known as “O” stars, concentrated within a diameter

of one light-year, making it the most compact cluster known in

the Milky Way galaxy.

The density of stars makes the region in and around the Arches

cluster a microcosm of what is likely occurring in starburst


“The Arches cluster is one of the best ‘local’ analogues of

starburst galaxies — the most prodigious stellar nurseries

known,” said Casey Law of the Harvard-Smithsonian Center for

Astrophysics, Cambridge, MA. “Yet the Arches cluster is in our

backyard, not millions of light-years away.”

Starburst galaxies are known for creating huge hot bubbles of

gas that escape from the galaxy. In a similar way, Chandra

observations of the Arches clusters may provide clues to the

origin of a much larger cloud of hot gas known to exist in the

galaxy’s center.

“Our data suggest that the gas within the Arches cluster may get

so hot that it escapes from the cluster,” said Cornelia Lang of

the University of Massachusetts, Amherst. “The Arches and other

clusters like it may contribute to the reservoir of mysterious

hot gas long observed near the Milky Way.”

Zadeh and his collaborators intend to search for X-ray emissions

from other clusters of stars near the galactic center and

compare this to newer, longer Chandra observations of the Arches


Chandra observed the Arches cluster region with its Advanced CCD

Imaging Spectrometer (ACIS). The research team for this

investigation included Casey Law and Antonella Fruscione from

the Harvard-Smithsonian Center for Astrophysics; Cornelia Lang

and Daniel Wang from University of Massachusetts; Mark Wardle of

the University of Sydney, Australia; and Angela Cotera from

University of Arizona, Tucson.

The ACIS X-ray camera was developed for NASA by The Pennsylvania

State University, University Park, and the Massachusetts

Institute of Technology, Cambridge. NASA’s Marshall Space Flight

Center in Huntsville, AL, manages the Chandra program for the

Office of Space Science, Washington, DC. TRW, Inc., Redondo

Beach, CA, is the prime contractor for the spacecraft. The

Smithsonian’s Chandra X-ray Center, Cambridge, MA, controls

science and flight operations.

Images associated with this release are available at: