Stellar astronomy research published by a UC Berkeley-led team Nov. 5 described what scientists believe is a never-before-seen type of supernova.

The team, led by Dovi Poznanski, a postdoctoral researcher at UC Berkeley and Lawrence Berkeley National Laboratory, discovered unique characteristics in data from a supernova observed in 2002 that have led to a whole new classification of supernovae.

The supernova, called SN 2002bj, occurred in the Lepus constellation about 163 million light-years away and exploded for a period of a little less than a month, which is much shorter than a typical supernova's period.

SN 2002bj was originally believed to be a supernova from a massive star that collapsed in on itself and exploded, known as a Type II supernova. Poznanski's team now believes that it was actually a special kind of Type Ia supernova that involves an exploding white dwarf.

A white dwarf is the next stage for a sun-like star after most of its nuclear fuel has been spent, a process that takes billions of years. The star then collapses to about the size of the Earth, and it becomes incredibly dense.

Douglas Leonard, who was a post-doctoral fellow at the University of Massachusetts at Amherst during his time on this project, said the two unique features of this supernova were its spectrum and its light curve.

The spectrum breaks the light up into colors-like rain does to sunlight to create a rainbow-and allows researchers to determine a supernova's chemical composition. The light curve measures how the brightness decays over time.

"This one brightened and faded much quicker than other known objects," said Leonard, currently an assistant professor of astronomy at San Diego State University. "(Also,) it had a weird mix of elements for a star that goes supernova."

He said this particular white dwarf in SN 2002bj is thought to have been part of a binary star system. The white dwarf was believed to be pulling matter from the other star before reaching a critical point and exploding, which closely matches a theory published in 2007 by a team led by UC Santa Barbara physics professor Lars Bildsten.

"We have some clues," Leonard said. "Then you run back to the theoretical papers written by scientists who don't spend their time observing, but thinking about (astronomy)."

The supernova was observed in 2002 at the Lick Observatory in San Jose.

Poznanski was looking through old supernova data for evidence of universe expansion for an unrelated project last June. Upon close examination, he noticed that data from SN 2002bj was not categorized correctly.

"After more enquiries and discussion with collaborators it became clear that nobody had seen anything like it," Poznanski said in an e-mail.

Tags: SUPERNOVA, LAWRENCE BERKELEY NATIONAL LABORATORY