Chandra Images A Young Supernova Blast Wave
The supernova named 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 over 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 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. 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 has 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.

Images and news stories on Chandra's progress can be found on the Internet at: http://chandra.harvard.edu. Also go to http://www.science.psu.edu

The backgrounder was written by David N. Burrows, senior scientist and professor of astronomy and astrophysics at Penn State, for a NASA press conference on 11 May 2000. For further comments, call 814-863-2466 or e-mail < >.