Supernova 1987A: Fast Forward to the Past (Forwarded)

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
(Phone: 617/496-7998)

August 17, 2005

Supernova 1987A: Fast Forward to the Past

Recent Chandra observations have revealed new details about the fiery ring
surrounding the stellar explosion that produced Supernova 1987A. The data
give insight into the behavior of the doomed star in the years before it
exploded, and indicate that the predicted spectacular brightening of the
circumstellar ring has begun.

The supernova occurred in the Large Magellanic Cloud, a galaxy only
160,000 light years from Earth. The outburst was visible to the naked eye,
and is the brightest known supernova in almost 400 years. The site of the
explosion was traced to the location of a blue supergiant star called
Sanduleak -69 202 (SK -69 for short) that had a mass estimated at
approximately 20 Suns.

Subsequent optical, ultraviolet and X-ray observations have enabled
astronomers to piece together the following scenario for SK -69: about ten
million years ago the star formed out of a dark, dense, cloud of dust and
gas; roughly a million years ago, the star lost most of its outer layers
in a slowly moving stellar wind that formed a vast cloud of gas around it;
before the star exploded, a high-speed wind blowing off its hot surface
carved out a cavity in the cool gas cloud.

The intense flash of ultraviolet light from the supernova illuminated the
edge of this cavity to produce the bright ring seen by the Hubble Space
Telescope. In the meantime the supernova explosion sent a shock wave
rumbling through the cavity.

In 1999, Chandra imaged this shock wave, and astronomers have waited
expectantly for the shock wave to hit the edge of the cavity, where it
would encounter the much denser gas deposited by the red supergiant wind,
and produce a dramatic increase in X-radiation. The latest data from
Chandra and the Hubble Space Telescope indicate that this much-anticipated
event has begun.

Optical hot-spots now encircle the ring like a necklace of incandescent
diamonds (image on right). The Chandra image (left) reveals
multimillion-degree gas at the location of the optical hot-spots.

X-ray spectra obtained with Chandra provide evidence that the optical
hot-spots and the X-ray producing gas are due to a collision of the
outward-moving supernova shock wave with dense fingers of cool gas
protruding inward from the circumstellar ring (see illustration). These
fingers were produced long ago by the interaction of the high-speed wind
with the dense circumstellar cloud.

The dense fingers and the visible circumstellar ring represent only the
inner edge of a much greater, unknown amount of matter ejected long ago by
SK -69. As the shock wave moves into the dense cloud, ultraviolet and
X-radiation from the shock wave will heat much more of the circumstellar
gas.

Then, as remarked by Richard McCray, one of the scientists involved in the
Chandra research, "Supernova 1987A will be illuminating its own past."

Additional information and images are available at:
http://chandra.harvard.edu/photo/2005/sn87a/