Star Burst Caught in Real Time - This Post - External Link

For the first time, scientists have observed the spectacular death of a massive star in real time.

Because the supernova lasted for nearly 40 minutes, NASA's Swift satellite was able to turn its lens towards the explosion to observe the star's slow death.

"Usually these gamma ray bursts last fractions of a second to a couple hundred seconds," said Alex Filippenko, professor of astronomy at the University of California, Berkeley. "This lasted many thousands of seconds.

"The Swift satellite finds these things as soon as they go off, but the longer they last the more we can watch in real time, and others can turn their telescopes to it in real time. This is a weird object (that has generated) four papers in Nature." The papers appear in the Aug. 31 issue.

The event may have lasted so long because the explosion ejected tons of debris that later interacted with gas in the vicinity of the star, said Filippenko, who authored two of the papers. He added that theorists have a puzzle on their hands because this type of behavior was not predicted.

Swift was able to engage all three of its instruments. Its Burst Alert Telescope detected the explosion and relayed its location within 20 seconds. An Ultraviolet Optical Telescope recorded high-resolution imagery, and an X-ray telescope measured radiation emission.

The burst occurred in February when a massive star, located 440 million light years away in the Aries constellation, collapsed. The radiation burst was relatively wimpy compared to most gamma-ray bursts, and the scientists are calling it an X-ray flash. It was also the second closest gamma-ray burst ever observed -- most are billions of light-years away.

The unique properties of the star's demise lead scientists to believe they've discovered a new class of stellar explosion that falls somewhere between gamma-ray bursts and more common supernovae.

"People used the think gamma-ray bursts had a standard energy, almost like cosmic candles," said Alicia Soderberg, a graduate student at the California Institute of Technology in Pasadena, California, and lead author of one the Nature papers. "This event lies between those two distributions. It shows that it's more of a continuum."

No matter where it lands in the continuum, the death of a star creates an amazingly powerful eruption that momentarily outshines an entire galaxy.

This star had a solar mass of 20, meaning it was about 20 times larger than the sun. That's about half the size of other massive stars that produce gamma rays as they die.

When the burning hydrogen that fuels a massive stars runs out, its core collapses into a compact object -- usually a neutron star or occasionally a black hole.

Scientists previously thought that all gamma-ray bursts were associated with black holes. But this recent explosion maybe have instead resulted in a neutron star.

"If that's the case, this suggests that even the formation of a neurtron star in a stellar explosion can in some cases be associated with the emission of very high-level radiation," Filippenko said. "That may well be the case but my own team and I will continue do investigation to gain confidence in that conclusion."

A similarly wimpy gamma-ray explosion was detected as recently as 1998, which suggests that these bursts could be 10 to 100 times more common than the more massive gamma-ray bursts, which are only detected every 10 to 20 years, Soderberg said. Until now, the less powerful events likely went undetected because they are wimpier than expected, and therefore not detected by gamma-ray satellites.

If the fact that these starbursts are so common sounds a bit scary -- and it should since one near the Milky Way could be quite destructive -- another new study could lend comfort, Soderberg said. A paper soon-to-be published in the Journal of Astrophysics and Astronomy speculates that the properties of our galaxy are not conducive to gamma ray bursts.

Soderberg had been focusing on this new type of explosion for four years while completing her graduate work. She said it's a relief to finally confirm the theory that these unique events exist, which astronomers took up after the 1998 stellar explosion. That burst was the closest gamma-ray burst ever observed, but it was surprisingly faint.

"We didn't know if it was real or maybe not real for many years," Soderberg said. "And now we know these events are true and not all gamma-ray bursts have the same energy."