Mystery of Ultra-Long Gamma Ray Bursts Solved: Death Throes of a Star

Massive, long-lived cosmic explosions have puzzled scientists since 2010 when they were first discovered on Christmas day. Now, though, researchers may have some new evidence about what causes these giant explosions; they could potentially be the violent death throes of a supergiant star.

These cosmic explosions create powerful blasts of high energy gamma-rays, known as gamma-ray bursts. While most similar explosions are over in just a minute, though, this new type can last for several hours. When the first of these long-lived explosions was detected, the readings neglected to calculate distance. This, in turn, caused two theories to arise as to the origins of the blast.

The first theory suggested that the explosion was due to an asteroid, shredded by the gravity of a dense neutron star in our galaxy. The second theory, in contrast, suggested that it was a supernova in a galaxy about 3.5 billion light years away.

"These events are among the biggest explosions in nature, yet we're only just beginning to find them," said Andrew Levan at the University of Warwick in a press release. 

Supernovas are essentially exploding stars. Extremely luminous, they cause a blast of radiation that can outshine an entire galaxy before fading from view over the course of several weeks or months. The blast can also expel much of the star's material into the surrounding interstellar medium.

In order to find out exactly which theory held true, astronomers looked for more examples of these cosmic explosions. In addition, they used data from the Gemini Telescope in Hawaii in order to examine the ultra-long gamma-ray burst that occurred in 2010. In particular, they were able to find that the explosion had a redshift of .847, which means that it had an approximate location of about seven billion light years away.

So what does that mean for the explosion? The burst could have been caused by a supergiant, a star about 20 times more massive than the sun. This huge star evolves to become among the biggest and brightest stars in the universe with a radius of up to one billion miles. It's possible that the ultra-long durations seen in 2010 are simply down to how large the star actually was--the gamma-ray bursts would have taken much longer to propagate through the star, so the blasts themselves last for a much longer time.

"We believe that powering the explosion is a newly formed black hole in the heart of the star," said Nial Tanvir, the second author of the study, in a press release. "The amazing thing is that nature seems to have found ways of blowing up a wide range of stars in the most dramatic and violent way."