Supernova size revises theory
The measurements taken at Mauna Kea break a physical limit
Astronomers using Mauna Kea telescopes to study stars exploding as supernovae saw something so surprising they say it "has opened up a Pandora's box."
The astronomers discovered a supernova more massive than they believed possible, which may change their thinking about how stars explode as supernovae, they said in a paper published today in the journal Nature.
Astronomers from the California Institute of Technology, University of Toronto and University of California at Berkeley made the discovery during a survey for distant supernovae at the Canada France Hawaii Telescope.
The program began in 2003 and involves 500 nights of observations over five years, Christian Veillet, executive director of the CFH telescope, said by telephone.
The scientists have looked at hundreds of Type 1a supernovae, thermonuclear explosions used to map the universe because they have about the same brightness, he said.
"All are behaving well, and suddenly they find one that is not behaving well, according to what we think."
The rogue supernova, named SNLS-03D3bb, was found in a galaxy 4 billion light years away.
It originated from a "white dwarf," a dense evolved star with a mass far larger than any previously seen, reported University of Toronto postdoctoral researcher Andy Howell, lead author of the study.
THE SUPERNOVA'S unusually large mass was calculated by Caltech astronomer Richard Ellis, using spectroscopy at the 10-meter Keck Telescope.
Veillet said the discovery "shows the synergy between two telescopes, which are different but each is unique."
The Canada France Hawaii 3.6-meter telescope isn't the largest on Mauna Kea, but has some very high-tech instruments "which allow us to be very competitive and to be a complement to the larger telescopes," he said.
The instruments include the biggest digital camera in the world, with a wide field covering an area as large as four full moons together, Veillet said.
University of Oklahoma professor David Branch, in a separate article on the research in Nature, called SNLS-03D3bb the "Champagne Supernova," in celebration of an explosion providing new insight into what makes supernovae.
The star reached about two solar masses before exploding, breaking a limit based on physical laws that a supernova explosion occurs when a white dwarf approaches 1.4 solar masses, the astronomers said.
"It should not be possible to break this limit," Howell said in a news release, "but nature has found a way. So now we have to figure out how nature did it."
"It looks like it requires a new physical explanation for supernova progenitors," said Steve Rodney, University of Hawaii Institute for Astronomy graduate student.
His dissertation is aimed at figuring out what Type 1a supernova are before they explode and become the bright objects seen at large distances, he said.
These supernovae are called "standard candles," he said, "because if you know how bright they are, as they move away the amount of dimming you get tells you how far away they are."
MAPPING DISTANCES with Type 1a supernovae led to the surprising discovery in 1998 that the expansion of the universe is accelerating and dark energy may be the source, Rodney noted.
"The problem when using these supernovae for distance measurement is they're a very useful tool, but we don't know exactly what they are," he added. "It's like trying to build a wall, but we don't know if we're holding a hammer or screwdriver."
The "Champagne Supernova" team, speculating on reasons why the white dwarf became so huge before exploding, said possibly the original star was rotating so fast that centrifugal force kept gravity from crushing it at the usual limit. Or the explosion could have resulted from two white dwarfs merging, they said.