June 9, 2011

New Class Of Supernova Brighter Than Any Seen Before

Astronomers announced on Wednesday a new class of supernova after observing six ultra-bright flashes of ancient exploding stars in deep space.

The explosions, which were ten times brighter than any other previously seen supernova, may illuminate star-forming clouds in far-off, primitive galaxies, allowing scientists to observe stellar creation.

The scientists directly observed four of these exploding stars, while another two previously unexplained supernovae are now believed to belong to this new class, the researchers said.

"We're learning about a whole new class of supernovae that wasn't known before," said Robert Quimby, a California Institute of Technology (Caltech) postdoctoral scholar and lead investigator of the explosions.

"We have a whole new class of objects that can't be explained by any of the models we've seen before," he said.

"What we do know about them is that they are bright and hot -- 10,000 to 20,000 degrees Kelvin; that they are expanding rapidly at 10,000 kilometers per second; that they lack hydrogen; and that they take about 50 days to fade away-much longer than most supernovae, whose luminosity is often powered by radioactive decay," he said.

"So there must be some other mechanism that's making them so bright."

"These new supernovae are very interesting, because they are 10 times more brilliant than the others and allow us to delve further in space and time... back to the first 10 percent of the age of the Universe," wrote French astronomer Francoise Combes in a commentary about Quimby's paper.

Scientists are not yet clear exactly what causes this brightness.

One idea is that the source is a "pulsating" star, an enormous star that blows off hydrogen-free shells of gas.   When the star eventually explodes as a supernova, the blast heats up the shells to intensely high temperatures, causing the luminosity.

Most supernovae occur when a star runs out of fuel, causing its core to collapse, triggering a massive explosion that leaves behind a neutron star or a black hole.

Another, more rare, type of supernova exists in which mass flows from a cooling ageing star known as a red star to a "white dwarf," the hot, dense core of an old star, which ultimately collapses in on itself and then explodes.

But the six supernovae reported by Quimby and his team exhibited none of the chemical signatures of these known supernovae.

Quimby began his investigation began in 2005, when he observed a supernova called SN 2005ap 100 billion times brighter than the Sun and twice as bright as the previous record-holding supernova.

Around the same time, the Hubble Space Telescope identified a supernova called SCP 06F6 that also had an odd chemical spectrum.

These findings triggered the formation of a special team to scan the universe for "transients," as ephemeral flashes are known.  The team utilized the added optical power of other telescopes in California, Hawaii and the Canary Island.

The work resulted in the four newly reported objects being added to the supernova net.  All of the supernovae exhibited atypical, hydrogen-less signatures and were found in small galaxies of a few billion stars known as dwarf galaxies.

The findings were published online June 8, 2011, in the journal Nature.


Image 1: The 1.2-meter Samuel Oschin Telescope at Palomar Observatory that was used to discover four supernovae of a new class. Inset: one of the newly discovered supernovae, PTF09cnd. Credit: Caltech/Scott Kardel/Robert Quimby/modified from Nature

Image 2: The four supernovae discovered by the Palomar Transient Factory. Left: before explosion. Right: after explosion. From top to bottom, the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr. Credit: Caltech/Robert Quimby/Nature


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