Astronomers using NASA’s Chandra X-ray Observatory discovered a mysterious
cloud of high-energy electrons enveloping a young cluster of stars. The
extremely high-energy particles could cause dramatic changes in the
chemistry of the disks that will eventually form planets around stars in the
cluster.
Known as RCW 38, the star cluster covers a region about five light years
across. It contains thousands of stars formed less than a million years ago
and appears to be forming new stars even today. The crowded environment of a
star cluster is thought to be conducive to the production of hot gas but not
high-energy particles. Such particles are typically produced by exploding
stars, in the strong magnetic fields around neutron stars or black holes,
none of which are evident in RCW 38.
“The RCW 38 observation doesn’t agree with the conventional picture,” said
Scott Wolk of the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Mass., lead author of an Astrophysical Journal Letters paper describing the
Chandra observation. “The data show that somehow extremely high-energy
electrons are being produced there, although it is not clear how,” he said.
Electrons accelerated to energies of trillions of volts are required to
account for the observed X-ray spectrum of the gas cloud surrounding the
ensemble of stars, which shows an excess of high-energy X-rays. As these
electrons move in the magnetic field that threads the cluster, they produce
X-rays.
One possible origin for the high-energy electrons is a previously undetected
supernova that occurred in the cluster. Although direct evidence for the
supernova could have faded away thousands of years ago, a shock wave, or a
rapidly rotating neutron star produced by the outburst, could be acting in
concert with stellar winds to produce the high-energy electrons.
“Regardless of the origin of the energetic electrons,” said Wolk, “their
presence would change the chemistry of proto-stellar disks in ways that
could still be manifest billions of years later.”
For example, in our own solar system, we find evidence of certain
short-lived radioactive nuclides (Aluminum 26 being the most well known).
This implies the existence of a high-energy process late in the evolution of
our solar system. If our solar system was immersed, for a time, in a sea of
energetic particles, this could explain the rare nuclides present in
meteorites found on Earth.
RCW 38 is approximately 6,000 light years from Earth. It is one of the
nearest star-forming regions with very young and hot stars. Other authors of
the paper, which appeared in the December 1, 2002 issue of the Astrophysical
Journal Letters, are Tyler Bourke, Randall Smith and Bradley Spitzbart of
the Harvard-Smithsonian Center for Astrophysics, and Joao Alves of the
European Southern Observatory in Garching, Germany.
NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra
program for the Office of Space Science in Washington. 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 and additional information about this result are available at:
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