NASA Scientists Witness a Supernova Cosmic Rite of Passage (Forwarded)

Susan Hendrix
Goddard Space Flight Center Greenbelt, Md. November 29, 2005
Phone: (301) 286-7745

RELEASE: 05-09

NASA Scientists Witness a Supernova Cosmic Rite of Passage

Scientists using NASA's Chandra X-ray Observatory have witnessed a cosmic
rite of passage, the transition from a supernova to a supernova remnant, a
process that has never been seen in much detail until now, leaving it
poorly defined.

A supernova is a massive star explosion; the remnant is the beautiful
glowing shell that evolves afterwards. When does a supernova become
supernova remnant? When does the shell appear and what powers its radiant
glow?

A science team led by Dr. Stefan Immler of NASA's Goddard Space Flight
Center, Greenbelt, Md., has taken a fresh look at a supernova that
exploded in 1970, called SN 1970G, just off the handle of the Big Dipper.
This is the oldest supernova ever seen by X-ray telescopes.

"Some astronomers have thought there's a moment when the supernova remnant
magically turns on years after the supernova itself has faded away, when
the shock wave of the explosion finally hits and lights up the
interstellar medium," said Immler. "By contrast, our results show that a
new supernova quickly and seamlessly evolves into a supernova remnant. The
star's own debris, and not the interstellar medium gas, fuels the
remnant."

These results appear in The Astrophysical Journal, co-authored by Dr. Kip
Kuntz, also of Goddard. They support previous Chandra observations of SN
1987A by Dr. Sangwook Park of Penn State.

Using new data from Chandra and archived data from the European-led ROSAT
and XMM-Newton observatories, Immler and Kuntz pieced together how SN
1970G evolved over the years. They found telltale signs of a supernova
remnant -- bright X-ray light -- yet no evidence of interstellar gas, even
across a distance around the site of the explosion 35 times larger than
our solar system.

Instead, the material that is heated by the supernova shock to glow in
X-ray light, what we call the remnant, is from the stellar wind of the
star itself and not distant gas in the interstellar medium. This wind,
comprising energetic ions, was shed by the progenitor star thousands to
million of years before the explosion. If this were from the interstellar
medium, it would be much denser than this stellar wind.

Immler and Kuntz next studied the density profiles of all other supernovae
that have been detected over the past two decades. Sure enough, the
low-density circumstellar matter from the stellar wind was the source of
X-rays, not the interstellar medium. Immler said that historical supernova
remnants such as Cassiopeia A, which exploded some 320 years ago, also
show no signs of activity from the interstellar medium.

This is more than just a name game, more than hypothetically changing SN
1970G to SNR 1970G. "We have to rethink this notion that a shock wave from
the supernova crashes into the interstellar medium to create a supernova
remnant," said Immler. "The luminous supernova remnants that we see can be
created without the need of a dense interstellar medium. In fact, our
study showed that all supernovae detected in X-rays over the past 25 years
live in a low-density environment."

SN 1970G is located in the galaxy M101, also called the Pinwheel Galaxy, a
stunning spiral galaxy about 22 million light years away in the
constellation Ursa Major, home of the Big Dipper. Although the galaxy
itself is visible from dark skies with binoculars, telescopes cannot
resolve much structure in SN 1970G, unlike for supernova remnants in our
Milky Way galaxy. Discovered with an optical telescope in 1970, SN 1970G
was not seen with X-ray telescopes until the 1990s.

Immler's work at NASA Goddard is supported through the Universities Space
Research Association. Kuntz is supported through University of Maryland,
Baltimore County. NASA¹s Marshall Space Flight Center in Huntsville, Ala.,
manages the Chandra program for the Agency¹s Science Mission Directorate.
The Smithsonian Astrophysical Observatory controls science and flight
operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu/photo/2005/sn70/
and
http://www.nasa.gov/centers/marshall/news/chandra/


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