Ultralong gamma-ray bursts may come from supergiant stars

Los Angeles Times : Gamma-ray bursts (GRBs), which are the most energetic explosions in the universe, are believed to be caused by the death of a massive star. Over the past four decades, thousands of GRBs have been observed. Until recently, scientists had classified GRBs as either short (lasting less than 2 seconds) or long (lasting 20â50 seconds). But new data, primarily from NASA’s Swift satellite, show that some GRBs can last for hours. At this week’s 2013 Huntsville Gamma-Ray Burst Symposium in Nashville, Tennessee, astronomers presented the latest theories regarding three of those ultralong bursts. Because the ultralong GRBs last up to 100 times as long as long GRBs, they must originate from a correspondingly large star. The researchers propose the most likely source to be blue supergiants, which contain 20 times the Sun’s mass and may be up to 1000 times its size. Although an ultralong GRB could cause major damage if one occurred near Earth, the researchers say such an explosion near us is unlikely because those GRBs tend to occur in galaxies composed mainly of hydrogen and helium, while our galaxy is rich in the heavier elements.