DEAD STAR RE-IGNITES AND EXPLODES

Early this year students at University College London's teaching observatory at Mill Hill detected a rare supernova explosion in the nearby M82 galaxy. These events occur in a galaxy typically only once every two hundred years.
http://www.bbc.co.uk/news/science-environment-28967741

The star was a dead star - a white dwarf - and the event is known as a Type 1a supernova.

Single white dwarfs just cool off slowly over time. But if the white dwarf star is able to acquire additional mass, either from a companion star or another white dwarf, its mass can exceed a threshold (called the  Chandrasekhar limit)  and a supernova explosion is initiated.

The theoretical mechanism is that the extra mass causes a nuclear fusion between carbon and oxygen atoms to give radioactive nickel, which decays via cobalt into iron. This decay chain generates gamma rays that give rise to the bright emission from the supernova.

Dr Eugene Churazov and colleagues studied these gamma rays between 50 and 100 days after the explosion. They detected the signature of the cobalt decay in the gamma ray profile and the amount of gamma emission matched the theoretical model for a white dwarf supernova.

However their results were not yet able to exclude the possibility that this event was caused by a merger of two white dwarfs, rather than by a white dwarf close to the Chandrasekhar limit acquiring additional mass from a companion star.

Comment: A remarkable investigation of a chance rare stellar event which was observed this year.