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Title : SHOCK WAVE SHEDS NEW LIGHT ON FADING SUPERNOVA
Author : unknown
Date :

NASA's Hubble Space Telescope is giving astronomers a
ringside seat to a never before seen titanic collision of an onrushing
stellar shock wave with an eerie glowing gas ring encircling a nearby
stellar explosion, called supernova 1987A.

Though the star's self-destruction was first seen nearly 11
years ago on Feb. 23, 1987, astronomers are just now beginning to
witness its tidal wave of energy reaching the "shoreline" of the
immense light-year wide ring.

Shocked by the 40-million mile per hour sledgehammer blow, a
100-billion mile diameter knot of gas in a piece of the ring has
already begun to "light up", as its temperature surges from a few
thousand degrees to a million degrees Fahrenheit.

"We are beginning to see the signature of the collision, the
hammer hitting the bell. This event will allow us to validate ideas we
have built up over the past ten years of observation," says Robert
Kirshner of the Harvard-Smithsonian Center for Astrophysics (CfA) in
Cambridge, MA. "By lighting up the ring, the supernova is exposing its
own past."

Astronomers predict it's only a matter of years before the
complete ring becomes ablaze with light as it absorbs the full force of
the crash.

Illuminating the surrounding space like a flashlight in a smoky
room, the glowing ring is expected to literally shed a brilliant new
light on many unanswered mysteries of the supernova: What was the
progenitor star? Was it a single star or binary system? Are a pair of
bizarre outer rings attached to an invisible envelope of gas connecting
the entire system?

"We have a unique opportunity to probe structure around the
supernova and uncover new clues to the final years of the progenitor
star before it exploded," adds Richard McCray of the University of
Colorado in Boulder, CO. "The initial supernova flash only lit up a
small part of the gas that surrounds the supernova. Most of it is
still invisible. But the light from the crash will give us a chance to
see this invisible matter for the first time, and then perhaps we can
unravel the mystery of the outer rings."

Though scientists will never solve the paradox of what happens
when an irresistible force meets an immovable object, the supernova
collision is the closest real-world example yet. "This supernova gives
us an unprecedented opportunity to directly witness new physics of
shock interactions," says McCray. "Though astronomers have measured
shock effects from the expanding debris of many supernovae which are
centuries-old, their impact velocities are at least ten times slower
than the ones we see today in supernova 1987A."

The ring was formed 20,000 years before the star exploded. One
theory is that it resulted from stellar material flung off into space
as the progenitor star devoured a stellar companion. The ring's
presence was given away when it was heated by the intense burst of
light from the 1987 explosion. The ring has been slowly fading ever
since then as the gas cools.

Several years ago radio waves and X-rays were detected as the
fastest moving explosion debris slammed into cooler invisible gas
inside the ring. In spring of 1997 the newly installed Space Telescope
Imaging Spectrograph (STIS) first measured the speed of the supernova
debris pushing along the shock wave. "The STIS lets you see the
invisible stuff," says George Sonneborn of Goddard Space Flight Center
in Greenbelt, MD. "We see the shock happening everywhere around the
ring." In July, Hubble Wide Field and Planetary Camera-2 images taken
by Robert Kirshner and co-investigators showed that a compact region
on the ring lit up like a sparkling diamond set in an engagement ring.

Supernova 1987A is the brightest stellar explosion seen since
Johannes Kepler observed a supernova in the year 1604. It is located
about 167,000 light-years from Earth in the Large Magellanic Cloud.

The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc., for NASA,
under contract with the Goddard Space Flight Center, Greenbelt, MD.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency.