back to news Jan. 20, 2016

Astronomers May Have Discovered the Most Powerful Supernova

An international team of astronomers including Professors Krzysztof Stanek, Christopher Kochanek and Todd Thompson in Ohio State's Department of Astronomy may have discovered the largest supernova ever seen from Earth. The exploding massive star is named ASASSN-15lh and is only 10 miles (16 kilometers) across at its core, yet it is much brighter than the entire output of the Milky Way. The team of astronomers released their findings this week in the journal Science.

“This may be the most powerful supernova ever seen by anybody … it’s really pushing the envelope on what is possible,” said study co-author Stanek.

ASASSN-15lh was first spotted in June of last year using the All Sky Automated Survey for Supernovae (ASAS-SN), based at of Ohio State. The intention of ASAS-SN is to get better statistics on the different types of supernovas and where they are occurring in the cosmos. The survey uses smaller telescopes to scan the sky every two to three days, searching for changes in the heavens. If some new bright object pops up, they’ll catch it, and astronomers can then use bigger telescopes to take a better look.

“We actually had it for a few weeks before we even noticed it because this really was very marginal detection,” Stanek said. “It actually took us another few weeks to realize we had an extreme case of a supernova because at first you don’t really know what was happening.”

ASASSN-15lh was so powerful that the authors suspect the original star must have been very massive. But the chemical signatures they see in its light suggest it is suspiciously low on hydrogen, says study co-author Thompson.

"It's weird for massive stars not to have hydrogen," he says, but not impossible. "Some stars eject all their hydrogen in explosive events before they die, others lose hydrogen to binary companions." While there are some superluminous supernovae like this one that are hydrogen poor, he says, their workings are poorly understood in general.

In addition to being unusually bright, the supernova comes from a neighborhood off the beaten path: Most superluminous supernovae come from galaxies smaller and dimmer than the Milky Way with high rates of star production. But ASASSN-15lh seems to sit in a galaxy more luminous and massive than our own.

Ohio State co-authors on the study include John Beacom, professor, physics and astronomy and director, Center for Cosmology and Astro-Particle Physics (CCAPP); astronomy graduate students Thomas Holoien, Jonathan Brown, and Gregory Simonian; and physics graduate student A. Bianca Danilet.

Read the entire press release, courtesy of Pam Frost Gorder, associate editor, Research and Innovative Communications.