Most-luminous, 16-km wide supernova discovered

A team of astronomers has discovered the most-luminous, 16-km wide supernova observed that is 200 times more powerful than the average supernova, 570 billion times brighter than our Sun and 20 times brighter than all the stars in our Milky Way Galaxy combined.

Called ASAS-SN-15lh, the newly found super-luminous supernova, situated 3.8 billion light years away, was discovered by the All Sky Automated Survey for SuperNovae team (ASAS-SN), an international collaboration headquartered at the Ohio State University.

It uses a network of 14-cm telescopes around the world to scan the visible sky every two or three nights looking for very bright supernovae.

Supernovae are violent stellar explosions and some of the brightest objects in the universe. Human records noting their existence date back nearly 2,000 years.

"On June 14 last year, we spotted a newly occurring explosion in a galaxy of an unknown distance Subsequent observations allowed the team to confirm the existence of the supernova ASAS-SN-15lh," said Benjamin Shappee from Carnegie Mellon University in a paper published in the journal Science.

As counterintuitive as it may sound, super-luminous supernovae are difficult for astronomers to spot. This is because they are rare and tend to form in low-luminosity galaxies with vigorous star formation.

The new supernova's spectra matched that of other hydrogen-poor super-luminous supernovae.

But it wasn't until further follow-up was conducted that the study's lead author Subo Dong of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University realised how unusual the supernova is.

The team determined that the galaxy where ASAS-SN-15lh formed is very atypical for a super-luminous supernova, which raises questions about how these types of supernovae form.

"The astounding amount of energy released by this supernova strains the magnetar-formation theory," Shappee explained.

More work will be necessary to understand this extraordinary object's power source and whether there are other similar supernovae out there in the universe, he added.

"The honest answer is at this point that we do not know what could be the power source for ASASSN-15lh," noted Subo Dong, lead author from the Kavli Institute for Astronomy and Astrophysics at Peking University.

He added that the discovery "may lead to new thinking and new observations of the whole class of superluminous supernova."