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late October of 1999, a supernova was detected in NGC 1637, a spiral galaxy
that is 25 million light years from Earth. Chandra observed the supernova
twice soon after the explosion. X rays, shown by contours overlaid on an
optical mage, were detected from 3 million degree gas produced by the supernova.
An X-ray source in the center of the galaxy was also detected.
NASA's Chandra X-ray Observatory captured a rare glimpse of X-radiation
from the early phases of a supernova, one of the most violent events in
nature. Although more than a thousand supernovae have been observed by
optical astronomers, the early X-ray glow from the explosions has been
detected in less than a dozen cases.
When combined with simultaneous observations by radio and optical telescopes,
the X-ray observations tell about the thickness of the shell that was
blown off, its density, its speed, and how much material was shed by the
star before it exploded.
Chandra observed an X-ray glow from SN1999em with the total power of
50,000 suns. Ten days later it observed the supernova for another nine
hours, and found that the X rays had faded to half their previous intensity.
The optical luminosity, which had the brightness of 200 million suns,
had faded somewhat less. No radio emission was detected at any time.
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Observations
by optical astronomers showed that SN1999em was a Type II supernova produced
by the collapse of the core of a star ten or more times as massive as the
sun. The intense heat generated in the collapse produces a cataclysmic rebound
that sends high speed debris flying outward at speeds in excess of 20 million
miles per hour. The debris crashes into matter shed by the former star before
the explosion. This awesome collision generates shock waves that heat expanding
debris to three million degrees. The X-ray glow from this hot gas was detected
by Chandra and gives astrophysicists a better understanding of the dynamics
of the explosion, as well as the behavior of the doomed star in the years
before the explosion. |
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