Supernova 1987A, which provided astronomers a spectacular show 10 years ago, is brightening once again as a rapidly expanding debris cloud from the original explosion slams into an enormous ring of hydrogen gas encircling the dying star.
Estimated to be roughly one light-year, or about 6 trillion miles, in diameter, the gas ring is believed to have formed from material expelled by the star before it shrank from a red supergiant into a blue supergiant some 20,000 years before exploding. The ring should brighten by a factor of 1,000 in both the visible and invisible portions of the light spectrum during the coming decade, according to astrophysicists Kazimierz Borkowski and John Blondin of North Carolina State University and Richard McCray of the University of Colorado at Boulder.
The brightening already is beginning to appear in x-ray emissions observed by the German-NASA ROSAT telescope and in radio emissions observed by the Australia Telescope array. The blast wave being pushed outward by the explosion apparently is encountering diffuse gas inside the ring, the researchers said.
By simulating these observations with a Cray supercomputer at the North Carolina Supercomputing Center, the researchers predict the blast wave will continue to brighten steadily until about 2007 A.D. Then it will strike the dense ring itself, causing a sudden, spectacular display.
"In a sense, this supernova is digging up its own past," said McCray. "It will light up the material that it spewed out long before the explosion occurred."
The research team presented their results at the winter meeting of the American Astronomical Society held Jan. 12 to Jan. 16 in Toronto.
Supernova 1987A is located in the Large Magellanic Cloud that is visible from the Southern Hemisphere. Light from the stellar explosion, which took some 160,000 years to reach Earth, was first detected by astronomers on Feb. 23, 1987.
Despite the dramatic brightening predicted by researchers, it's doubtful the huge ring will be visible to the naked eye as was the original supernova, McCray said. "But it will be a prime target for astronomers for many years to come."
Astronomers are planning to follow the "renaissance" of 1987A with the Hubble Space Telescope. A new imaging spectrometer built by Ball Aerospace of Boulder, Colo., will be added to the orbiting observatory's scientific arsenal during a February 1997 servicing mission, allowing astronomers to see the blast wave at ultraviolet wavelengths and to track its motion as it approaches the ring.
Astronomers also will be able to observe x-rays from the impact using NASA's AXAF telescope following its 1998 launch, the researchers said.
The glowing ball of supernova debris inside the ring is expanding at a rate of more than 5 million miles per hour, said McCray, and the invisible blast wave is expanding roughly twice that fast. In contrast, the gaseous ring is expanding at the comparatively sluggish rate of about 20,000 miles per hour.
The ring is actually the innermost of three rings now encircling the supernova, McCray said. Two other much larger rings, which he dubbed "wagon wheels," can be seen in astronomical images looping trillions of miles outside the innermost ring.
"The origin of these rings is one of many unsolved mysteries left by the supernova," he said. "It's been fading for 10 years, but now it is becoming rejuvenated. The new light from the impact will give us a better chance to solve these mysteries."
Borkowski and Blondin are professors of physics at North Carolina State University. McCray is a professor of astrophysics and a fellow of JILA at CU-Boulder. JILA is a joint institute of CU-Boulder and the National Institute of Standards and Technology.
The research effort was supported by grants from NASA to North Carolina State University and CU-Boulder.