The Hubble Space Telescope has taken a close-up look at a strange event in the aftermath of a supernova: the sudden brightening of a huge gas ring that circles the exploding star. Astronomers think the ring is flaring up as it is smashed by debris from the immense explosion.
The 1987 supernova, which occurred a mere 170,000 light-years from Earth, was the first that could be studied in detail with modern telescopes. In 1989, astronomers discovered that a gas ring surrounds the exploding star at a distance of about 2 light-years; 5 years later, the Hubble Space Telescope discovered two other rings, larger but somewhat fainter, placed in two equidistant planes behind and in front of the star. The rings probably escaped from the star some 20,000 years before it exploded, but it's still unclear how that happened, says Dick McCray of the University of Colorado, Boulder.
In December, a team at the Cerro Tololo Inter-American Observatory (CTIO) in La Serena, Chile, first noticed that the central ring was lighting up in the infrared-spectrum. Shortly after, astronomers using the Hubble Space Telescope reported seeing the same spectacle at visible wavelengths. The brightening occurs as remnants of the supernova collide with the ring, causing tremendous shock waves and heating the gas to millions of degrees, says CTIO's Patrice Bouchet.
Closer scrutiny may shed more light on the ring's origins, says his colleague Arlin Crotts, and scientists may glean even more information as the debris from the blast keeps spreading. "The shock wave is going to stop for a while at this dense ring," says Crotts, "but it's going to continue to move above and below the ring, and keep running into things."