Washington, Oct 11 : Astronomer Robert Quimby has found the most luminous supernova ever for the second time round.

Quimby discovered the current record holder, supernova 2006gy, last year as part of his Texas Supernova Search project.

Now, he has announced that a supernova he discovered earlier in the project is twice as luminous.

He used follow-up studies to pinpoint its distance, and found that supernova 2005ap peaked at more than 100 billion times the brightness of the Sun.

Quimby said the supernova is a Type II, because it contains hydrogen.

Most Type II supernovae are thought to result when the cores of massive stars, those seven to eight times or more heavy than the Sun, collapse under their own weight and trigger an explosion.

This particular Type II is 300 times brighter than average, and lies in a dwarf galaxy in the constellation Coma Berenices, well behind the famous Coma cluster of galaxies.

“It's clearly not the same as 2006gy. It's a puzzle,” said Quimby's colleague and supernova expert J. Craig Wheeler of The University of Texas at Austin.

Quimby studied 2005ap with the giant 10-meter-class Hobby-Eberly Telescope (HET) just a few days after its discovery with the 18-inch ROTSE-IIIb robotic telescope on McDonald Observatory's Mount Fowlkes, a tiny neighbour compared to the HET.

Quimby’s Texas Supernova Search project uses the McDonald Observatory.

Quimby said the results were intriguing. The supernova's spectrum hinted at the presence of a highly shifted absorption line of oxygen III (an oxygen atom that has lost two of its electrons).

Quimby said if the feature was oxygen III, then 2005ap was “possibly very far away and thus very luminous”.

Incidentally, follow-up observations with the Keck Telescope in Hawaii by Quimby's colleague Greg Aldering of Lawrence Berkeley National Lab not only confirmed Quimby's HET detection of oxygen III, but added another, equally shifted element to the spectrum: magnesium.

Together, the studies confirmed 2005ap's distance of 4.7 billion light-years. (In astronomical terms, this equates to a redshift of z = 0.2832.)

Quimby said it was this distance measurement, combined with measurements of the supernova's apparent brightness that allowed the calculation of its intrinsic brightness, or “luminosity,” and uncovered 2005ap as the most powerful supernova yet.

“Before 2006gy, I thought this should not be plausible. There I was finding my first supernovae. I was just happy to get anything. It turned out to be the most luminous supernova ever found,” Quimby said.

The results are scheduled for publication in the October 20 edition of The Astrophysical Journal Letters. (ANI)