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Tuesday, December 21, 1999
Joseph Blumberg
Rutgers Office of Media Relations
732/932-7084, extension 652
E-mail: blumberg@ur.rutgers.edu
http://ur.rutgers.edu/medrel
Steve Roy
Marshall Space Flight Center, Huntsville, AL
Phone: 256-544-6535
http://www.msfc.nasa.gov/news
Dr. Wallace Tucker
Chandra X-ray Observatory Center
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
Phone: 617-496-7998
http://chandra.harvard.edu
A team of astronomers led by Dr. John Hughes of Rutgers University in Piscataway,
NJ has used observations from NASA's orbital Chandra X-ray Observatory to make an
important new discovery that sheds light on how silicon, iron, and other elements
were produced in supernova explosions. An X-ray image of Cassiopeia A (Cas A), the
remnant of an exploded star, reveals gaseous clumps of silicon, sulfur, and iron
expelled from deep in the interior of the star.
The findings appear online in the Astrophysical Journal Letters at
http://www.journals.uchicago.edu/ApJ/journal/contents/ApJL/v528n2.html
and are slated for print publication on Jan. 10, 2000. Authors of the paper, "Nucleosynthesis
and Mixing in Cassiopeia A", are Hughes, Rutgers graduate student Cara Rakowski,
Dr. David Burrows of the Pennsylvania State University, University Park, PA and Dr.
Patrick Slane of the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA.
According to Hughes, one of the most profound accomplishments of twentieth century
astronomy is the realization that nearly all of the elements
other than hydrogen and helium were created in the interiors of stars. "During
their lives, stars are factories that take the simplest element, hydrogen, and convert
it into heavier ones," he said. "After consuming all the hydrogen in their
cores, stars begin to evolve rapidly, until they finally run out of fuel and begin
to collapse. In stars ten times or so more massive than our Sun, the central
parts of the collapsing star may form a neutron star or a black hole, while the rest
of the star is blown apart in a tremendous supernova explosion." Supernovae
are rare, occurring only once every 50 years or so in a galaxy like our own.
"When I first looked at the Chandra image of Cas A, I was amazed by the clarity
and definition," said Hughes. "The image was much sharper than any previous
one and I could immediately see lots of new details."
Equal in significance to the image clarity is the potential the Chandra data held
for measuring the composition of the various knots and filaments of stellar material
visible in Cas A. Not only could the astronomers determine the composition of many
knots in the remnant from the Chandra data, they were also able to infer where in
the exploding star the knots had originated.
For example, the most compact and brightest knots were composed mostly of silicon
and sulfur, with little or no iron. This pointed to an origin deep in the star's
interior where the temperatures had reached three billion degrees during the collapse
and resulting supernova. Elsewhere, they found fainter features that contained significant
amounts of iron as well as some silicon and sulfur. This material was produced even
deeper in the star, where the temperatures during the explosion had reached higher
values of four to five billion degrees.
When Hughes and his collaborators compared where the compact silicon-rich knots and
fainter iron-rich features were located in Cas A, they discovered that the iron-rich
features from deepest in the star were near the outer edge of the remnant. This meant
that they had been flung the furthest by the explosion that created Cas A. Even now
this material appears to be streaming away from the site of the explosion with greater
speed than the rest of the remnant.
By studying the Cas A Chandra data further, astronomers hope to identify which of
the several processes proposed by theoretical studies is likely to be the correct
mechanism for explaining supernova explosions, both in terms of the dynamics and
elements they produce.
"In addition to understanding how iron and the other elements are produced in
stars, we also want to learn how it gets out of stars and into
the interstellar medium. This is why the study of supernovae and supernova
remnants is so important," said Hughes. "Once released from stars, newly-created
elements can then participate in the formation of new stars and planets in a great
cycle that has gone on numerous times already. It is remarkable to realize that our
planet Earth and indeed even humanity itself is part of this vast cosmic cycle."
The Chandra observation was taken with the Advanced CCD Imaging Spectrometer (ACIS)
on August 19, 1999. ACIS was built by Pennsylvania State University, and the Massachusetts
Institute of Technology, Cambridge, MA.
To follow Chandra's progress, visit the Chandra site at:
http://chandra.harvard.edu
AND
http://chandra.nasa.gov
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.
This image will be available on NASA Video File which airs at noon, 3:00 p.m., 6:00
p.m., 9:00 p.m. and midnight Eastern Time. NASA Television is available on GE-2,
transponder 9C at 85 degrees West longitude, with vertical polarization. Frequency
is on 3880.0 megahertz, with audio on 6.8 megahertz.
High resolution digital versions of the X-ray image (JPG, 300 dpi TIFF ) and other
information associated with this release are available on the Internet at:
http://chandra.harvard.edu/photo/casajph/
or via links in: http://chandra.harvard.edu
-end-
EDITOR'S NOTE: For more information, contact John P. Hughes who is currently on-leave
in France but can be reached by telephone: 33-1-69-08-43-84 or e-mail at
jph@physics.rutgers.edu
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Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Cambridge, MA 02138 USA
Press Line: 617.496.7998 Fax: 617.495.7356
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Revised: 12/21/99
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