Cosmic explosion challenges astronomers’ knowledge of exploding stars

Evidence of an enormous explosion that occurred more than two billion years ago has revealed important information about the extreme environment in the central, hidden, part of galaxies.

A team of astronomers, including Dr Cosimo Inserra from the University of Southampton, detected the new type of explosion in a distant galaxy during all-sky surveys published this week in the Nature Astronomy journal.

The explosion, known as PS1-10adi, is thought to occur in active galaxies that house supermassive black holes consuming the gas and material around them.

The observed event occurred 2.4 billion years ago, but the gigantic distance that its light had to travel to reach Earth meant it couldn’t be seen by astronomers until 2010. The slow evolution of the explosion allowed scientists to monitor it for several years.

During the international study telescopes on Spanish island La Palma and Pacific island Hawaii detected the event that was so energetic that there were only two possible scenarios that could explain it. The first option was a massive star – hundreds of times larger than our Sun – exploding as a supernova. The second possibility was a lower mass star that would have been shredded by the ultra-strong gravitational forces close to the supermassive black hole.

Postdoctoral Fellow Dr Cosimo Inserra from the Southampton Theory Astrophysics and Gravity (STAG) Research Centre tested the data using established physical supernova models to support the results.

“The discovery we made has revealed explosions capable of releasing an amount of energy ten times bigger than normal explosions,” he explains. “Our data shows that events like this are not very unusual and challenges our knowledge of exploding and disrupting stars.”

Lead author Dr Erkki Kankare, of Queen’s University Belfast, adds: “If these explosions are tidal disruption events – where a star gets sufficiently close to a supermassive black hole’s event horizon and is shredded by the strong gravitational forces – then its properties are such that it would be a brand new type of tidal disruption event.

“If they are supernova explosions then their properties are more extreme than we have ever observed before, and are likely connected to the central environments of the host galaxies.”

The international team included research institutes from Finland, Sweden, Ireland, Italy, Spain, Chile, and the US.