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Astronomers find a supernova that is so bright it only existed in theory

An international team of astronomers led by the University of Birmingham has discovered the most massive supernova that has ever been identified. The stellar explosion has at least twice the power and luminosity of any known supernova.

The experts believe the newly-identified supernova, SN2016aps, is the result of a theoretical event that occurs when two massive stars merge before exploding. This would be the very first record of the phenomenon, pulsational pair-instability, which has never been confirmed through observation.

“We can measure supernovae using two scales – the total energy of the explosion, and the amount of that energy that is emitted as observable light, or radiation,” explained study lead author Dr. Matt Nicholl.

“In a typical supernova, the radiation is less than 1 percent of the total energy. But in SN2016aps, we found the radiation was five times the explosion energy of a normal-sized supernova. This is the most light we have ever seen emitted by a supernova.”

For a supernova to contain this much radiant power, the explosion must have been far more energetic than what is typically observed. An analysis of the light spectrum revealed that the explosion was energized by a powerful collision between the supernova and a massive shell of gas.

“While many supernovae are discovered every night, most are in massive galaxies,” said study co-author Dr. Peter Blanchard of Northwestern University.”This one immediately stood out for further observations because it seemed to be in the middle of nowhere. We weren’t able to see the galaxy where this star was born until after the supernova light had faded.”

After two years of observation, the explosion faded to one percent of its peak brightness. Based on these measurements, the researchers determined that the mass of the supernova was between 50 to 100 times greater than our sun, or 50 to 100 solar masses. Supernovae usually have between 8 and 15 solar masses.

“Stars with extremely large mass undergo violent pulsations before they die, shaking off a giant gas shell. This can be powered by a process called the pair instability, which has been a topic of speculation for physicists for the last 50 years,” said Dr. Nicholl. “If the supernova gets the timing right, it can catch up to this shell and release a huge amount of energy in the collision. We think this is one of the most compelling candidates for this process yet observed, and probably the most massive.”

“SN2016aps also contained another puzzle. The gas we detected was mostly hydrogen – but such a massive star would usually have lost all of its hydrogen via stellar winds long before it started pulsating. One explanation is that two slightly less massive stars of around, say 60 solar masses, had merged before the explosion. The lower mass stars hold onto their hydrogen for longer, while their combined mass is high enough to trigger the pair instability.”

Study co-author Professor Edo Berger of Harvard University explained that the discovery of this supernova could not have happened at a better time. “Now that we know such energetic explosions occur in nature, NASA’s new James Webb Space Telescope will be able to see similar events so far away that we can look back in time to the deaths of the very first stars in the Universe,” said Professor Berger.

The study is published in the journal Nature Astronomy.

By Chrissy Sexton, Staff Writer


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