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Chandra
Images a Young Supernova
Two images made by NASA's Chandra
X-ray Observatory, one in October 1999, the other in January 2000,
show for the first time the full impact of the actual blast wave from
Supernova 1987A (SN1987A). The
observations are the first time that X-rays from a shock wave have been
imaged at such an early stage of a
supernova explosion.
Recent observations of SN1987A with the Hubble
Space Telescope revealed gradually brightening hot spots
from a ring of matter ejected by the star thousands of years before it
exploded. Chandra's X-ray images show
the cause for this brightening ring. A shock wave is smashing into portions
of the ring at a speed of 10 million miles per hour (4,500 kilometers
per second). The gas behind the shock wave has a temperature of
about 10 million degrees Celsius, and is visible only with an X-ray telescope.
"With Hubble we heard the whistle from the oncoming train," said David
Burrows, senior scientist and
professor of astronomy and astrophysics
at Penn State and the leader of the team of scientists involved in
analyzing the Chandra data on SN 1987A. "Now, with Chandra, we can see
the train."
The X-ray observations appear to confirm the general outlines of a model
developed by team member Richard McCray of the University
of Colorado and others, which holds that a shock wave has been moving
out ahead of the debris expelled by the explosion.
As this shock wave collides with material outside the ring, it heats
it to millions of degrees. "We are witnessing the birth of a supernova
remnant for the first time," McCray said.
The Chandra images clearly show the previously unseen, shock-heated matter
just inside the optical ring.
Comparison of observations made with Chandra in October and January, and
with Hubble in February 2000, show the X-ray emission peaks close to the
newly discovered optical hot spots, and indicate the wave is beginning
to hit the ring.
In the next few years, the shock wave will light up still more material
in the ring, and an inward moving, or reverse, shock wave will heat the
material ejected in the explosion itself. "The supernova is digging up
its own past," said McCray.
The observations were made on October 6, 1999, using the Advanced
CCD Imaging Spectrometer (ACIS) and the
High Energy Transmission Grating Spectrometer, and again on January
17, 2000, using ACIS. Other members of the team were Eli Michael
of the University of Colorado; Una Hwang, Steven Holt and
Rob Petre of NASA's Goddard
Space Flight Center in Greenbelt, Maryland; and professors Gordon
Garmire and John Nousek of Penn
State.
The results will be published in an upcoming issue of the Astrophysical
Journal.
Chandra X-Ray Center
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Researcher Puts Cosmic Explosion
Into Common Terminology
By David Burrows
Senior Scientist and Professorof Astronomy and Astrophysics
SN1987A exploded in the Large Magellanic Cloud 13 years
ago, and is now on the threshold of changing from a freely
expanding explosion to a supernova remnant, as the blast
wave from the explosion begins to heat circumstellar gas.
The Chandra
X-ray Observatory has now dramatically captured the
first X-ray images of the birth of a supernova remnant.
We see a shell of hot gas, heated to a temperature of more
than 10 million degrees by the explosion.
To understand the significance of this image, consider
what happens in any large explosion, such as you may see
in movies. An observer at some distance from the explosion
first sees a bright flash of light, followed after a short
time by a shock wave and the sound of the explosion.
In the case of SN1987A, the explosion was so enormous that
the remnants of the star were blasted out at speeds of over
10,000 miles per second (1/20 of the speed of light).
The flash of light from this explosion illuminated a ring
of gas around the star, which is still visible in images
made by the Hubble Space
Telescope (HST).
Now the shock wave from the explosion is about to hit that
same ring of gas. Our X-ray image shows the prequel
of this cosmic collision, a region of invisible, ionized
gas just inside the ring that has been heated by this shock
wave to temperatures higher than the temperature at the
center of the Sun.
When you heat something up to high enough temperatures,
it glows. Think of a heating element on a stove, or
a piece of steel in a forge. As the temperature goes
up, it changes from a dull red to a bluish-white as it gets
hotter. If you could continue to heat it without melting
it, it would eventually get so hot that the light would
come primarily in the form of X-rays. This is what
is happening to this shock-heated gas around SN1987A.
The optical light seen by HST comes from relatively cool
gas--only a few thousand degrees! In order to see
this extremely hot gas, you have to observe it with X-ray
telescopes.
Supernova explosions are among the largest explosions in
the universe. In addition to the intrinsic interest
that they have simply because of their unimaginable energy
release, they are very important in the evolution of the
universe because they are responsible for creating and mixing
many of the elements common on Earth into the interstellar
medium (the gas between the stars, from which all future
stellar systems and planets are formed).
The atoms in your body, in the chair you are sitting in,
and in the Earth we live on, were produced by nuclear fusion
in the interior of stars, and were dispersed into the interstellar
medium in supernova explosions. In the process of
mixing with the interstellar medium, a supernova remnant
is created. The youngest supernova remnants that we
can observe today are about 400 years old, and were created
by three supernova explosions that occurred around the turn
of the 17th century. There had not been another nearby,
bright supernova explosion since then, until 1987.
This Chandra observation of SN1987A lets us observe the
actual birth of a supernova remnant for the first time,
and lets us test our theoretical models against observational
data.
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