Cosmic explosions give dark energy clues

Light from exploding stars is improving the astronomical "yardstick" used to calculate the acceleration of the expansion of the universe, U.S. scientists say. The light from two supernovae, massive stars that exploded hundreds of millions of years ago, has recently reached Earth, Southern Methodist University researchers said. A supernova discovered Feb. 6 exploded about 450 million years ago, while a second supernova discovered Nov. 20 exploded about 230 million years ago, Farley Ferrante, an SMU graduate student who made the initial Feb. 6 observation, said. Both are Type 1a supernovae, the result of white dwarf explosions, he said. "We call these Type 1a supernovae standard candles," Ferrante said. "Since Type 1a supernovae begin from this standard process, their intrinsic brightness is very similar. So they become a device by which scientists can measure cosmic distance." Type 1a supernova provide astronomers with indirect information about dark energy, which makes up 73 percent of the mass-energy in the universe and is theorized as being responsible for the accelerating expansion of our universe at various times after the Big Bang. "Every exploding star observed allows astronomers to more precisely calibrate the increasing speed at which our universe is expanding," Ferrante said. "The older the explosion, the farther away, the closer it was to the Big Bang and the better it helps us understand dark energy."