Diagram courtesy Nature and Robert Quimby/Caltech
Published June 8, 2011
A new type of exploding supernova has been discovered that's at least ten times brighter than any known supernova, a new study says.
"In the hundred years or so of studying supernovae, we thought we had seen it all—so this is pretty unexpected and exciting," said study leader Robert Quimby, an astronomer at the California Institute of Technology in Pasadena.
"After all this time, it's amazing that we are only just now finding a whole new class of events that outshines all other supernovae."
Considered some of the most violent and energetic events in the universe, supernovae can easily outshine their host galaxies for several weeks. Supernovae occur when stars with at least ten times the mass of our sun reach the end of their lives and explode.
That leaves a spinning, hot core called a neutron star, which is surrounded by a quickly expanding cloud of glowing gas. Their brilliant explosions are also used to measure large distances in the universe.
Newfound Supernovae Are Odd "Beasts"
Quimby and his team recently stumbled across six unusually bright supernovae using the Samuel Oschin Telescope at California's Palomar Observatory.
The odd light patterns were seen in dwarf galaxies ranging in distance from three billion to eight billion light-years away.
Until now astronomers have observed two general types of supernovae. A Type I supernova results when a star draws matter in from a companion star and dumps the matter on the first star's surface until a runaway nuclear reaction ignites the matter. In a Type II supernova, a supergiant star runs out of nuclear fuel and collapses under its own gravity until it detonates. (See supernova pictures.)
The newly spotted supernovae, however, don't seem to fit into either of these two categories—all six of them had never-before-seen properties. For example, the new supernovae showed not only unusually high emissions of ultraviolet radiation, but also extended periods of brightness, Quimby said.
"These stars show a much slower rise to maximum brightness than expected, taking a month or two to reach their peak—whereas a normal supernova can do that in only 17 days," he said.
"They then drop their brightness three times faster than normal. At this point we honestly don't know what is powering these beasts, but it must be some kind of exotic process going on."
One theory is that a bubble of hot gas is cast off from a dying star—at least a hundred times the mass of the sun—years before the star dies.
When the star eventually goes supernova, it ejects radioactive material that slams into the bubble, making it glow exceptionally bright, said Quimby, whose study appears tomorrow in the journal Nature.
Supernovae are of interest to scientists because they can actually blow out gas from their host galaxies and enrich the matter that fills the space between star systems with heavier elements.
"Supernovae can actually change the evolution of the galaxies themselves, and this means that the next generation of stars will evolve differently because of this metal enrichment," Quimby noted.
Now Quimby and his team are on the hunt for more of these new superbright supernovae, and they hope to probe younger galaxies at even greater distances.
"These long-lived supernovae may actually light up their surroundings, giving us a chance to probe the chemistry of the gas and dust that makes up its host galaxy—something we haven't been really been able to do yet."
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