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Lighting Up the Small Magellanic Cloud
By Greg Clark
Staff Writer
posted: 04:00 pm ET
14 April 2000
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chandra_image_000413 A colorful new image produced by melding data from optical, radio and X-ray telescopes shows the high-powered shock waves that linger in the aftermath of supernova explosions -- the dramatic death throes of massive stars. The image, which was made possible by new pictures from the Chandra X-ray Observatory, the Hubble Space Telescope, and ground-based telescopes, shows a relatively young remnant as it appeared just 1,000 years after it's parent star annihilated itself in a tremendous explosion. The supernova remnant, known as E 0102-72, is about 190,000 light-years from Earth in a neighboring galaxy called the Small Magellanic Cloud. The "cloud" is the third-nearest galaxy to the Milky Way, and is in the constellation Tucana, visible in the Southern Hemisphere. The bright blue ring in the image (above) is about 10 light-years across. It shows the X-ray emissions detected by the Chandra telescope. These X-rays are produced by gas that has been heated to millions of degrees Celsius by a shock wave rebounding toward the center of the supernova. The shock wave from the E 0102 explosion initially expanded outward at more than 12 million m.p.h. (20 million kilometers per hour). As it spread through space, it collided with the surrounding gas and charged particles, producing a rebounding shock wave that ricocheted inward. Analysis of the X-ray emissions reveals that the superheated gas is mostly oxygen and neon -- elements that are forged in nuclear reactions at the cores of stars. Radio emissions are shown in red, while the green represents visible light emitted by hot oxygen gas. 
This grayscale picture of a Chandra image shows two shock waves: the outer blast wave moving into the surrounding interstellar gas, and a reverse shock wave (dark inner ring) that it moving back into the gas blown off by the explosion. The X-rays from the reverse shock are more intense because the gas is denser there. What makes this supernova remnant stand out is that it has a very large quantity of oxygen compared to hydrogen, said Terrance Gaetz, an astrophysicist at the Smithsonian Astrophysical Observatory, the institution that manages Chandra. One explanation for the preponderance of oxygen is that the parent star was very large and old, and had blown away most its hydrogen as stellar wind before it exploded. Because the remnant is young it could prove to be a valuable object for learning about the physics of supernova explosions, Gaetz said. Most known remnants are seen only after the rebounding shock wave has collapsed into its center and dissipated, he said.
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