Now you see it. Supernova 2005ap (bottom) briefly outshines its whole galaxy and several neighboring galaxies (A-D) after appearing in a sky survey. Credit: SDSS/R. Quimby/ McDonald Obs./University of Texas, Austin

Just as in sports, astronomical records are made to be broken, and the latest one is a doozy: a supernova that briefly outshone the sun by a factor of 100 billion, doubling the brilliance of the previous record holder. Astronomers don't yet know which particular conditions could have triggered such "extraordinary luminosity," as the team that discovered the supernova writes in the 20 October issue of The Astrophysical Journal Letters. But whatever those conditions are, they figure to cause a theoretical rethinking of these titanic explosions.

Stars--those peaceful pinpoints of light in the night sky--are actually cauldrons of extreme temperatures and pressures. When the nuclear reactions that power them run out of fuel, the sun can no longer resist their own intense gravity; they collapse and trigger the massive explosions called supernovae. Astronomers have used automated sky searches to collect data on supernovae for decades. The findings have become so routine that scientists have classified supernovae into neat little categories, such as Type Ia, whose brightness occurs with such consistency it has become the standard candle for computing distances to other galaxies.

The new findings may challenge this orderliness. Supernova 2005ap seems to defy classification. The team of astronomers who discovered it--led by Robert Quimby of the California Institute of Technology (Caltech) in Pasadena--tentatively have labeled the 4.7 billion light-years away ex-star a Type II-L supernova because of its brightness and because its light spectrum shows a primarily hydrogen content. But the researchers are at a loss to explain the supernova's spectacular incandescence.

"We really don't know what made 2005ap so luminous," Quimby says. "Our best guess is that prior to the explosion, the star cast off some shell of material, and the supernova ejecta later collided with this shell." The problem, he says, is there still needs to be an unusually powerful engine driving the ejecta, so 2005ap could represent a new and rare class of supernovae. Some clues include the fact that the explosion achieved its peak brilliance far more rapidly than normal and then nearly as quickly dimmed. Also, the supernova's light spectrum shows the presence of forms of carbon, nitrogen, and oxygen atoms that are considered unprecedented. Only sightings of similarly bright supernovae will help solve the mystery, and Quimby is optimistic they will be found.

With the discovery of 2005ap--and its record-holding predecessor, called 2006gy (ScienceNOW, 7 May)--"the supernova bestiary is clearly enlarged," says astronomer Shri Kulkarni, also of Caltech but not involved in the research. He says because both events "are much more energetic than ordinary supernovae," they might somehow be linked to the same phenomena, such as gamma ray bursts or the birth of black holes.

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