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GRB 101225A, better known as the "Christmas burst," was an unusually long-lasting gamma-ray burst. Because its distance was not measured, astronomers came up with two radically different interpretations. In the first, a solitary neutron star in our own galaxy shredded and accreted an approaching comet-like body. In the second, a neutron star was engulfed by, spiraled into and merged with an evolved giant star in a distant galaxy. Now, thanks to a measurement of the Christmas burst's host galaxy, astronomers have determined that it represented the collapse and explosion of a supergiant star hundreds of times larger than the Sun.Music: Revelation of OneFor complete transcript, click here. Astronomers suggest that blue supergiant stars may be the most likely sources of ultra-long GRBs. These stars hold about 20 times the Sun's mass and may reach sizes 1,000 times larger than the Sun, making them nearly wide enough to span Jupiter's orbit. Credit: NASA's Goddard Space Flight Center/S. Wiessinger Astronomers suggest that blue supergiant stars may be the most likely sources of ultra-long GRBs. These stars hold about 20 times the Sun's mass and may reach sizes 1,000 times larger than the Sun, making them nearly wide enough to span Jupiter's orbit. Unlabeled. Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun. Unlabeled.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun. Unlabeled.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Blue supergiant star to scale with the Sun. Unlabeled.Credit: NASA's Goddard Space Flight Center/S. Wiessinger Three recent GRBs (blue dots) emitted high-energy gamma-ray and X-ray light over time spans up to 100 times greater than typical long bursts and constitute a new ultra-long class. This plot compares the energy received and the event duration among different classes of transient high-energy events: long GRBs (green); the disruption of an asteroid or comet by a neutron star or stellar-mass black hole in our own galaxy, or the break-out of a supernova shock wave in another galaxy (orange); and the tidal disruption of a star by a supermassive black hole in another galaxy (purple). Credit: NASA's Goddard Space Flight Center, after B. Gendre (ASDC/INAF-OAR/ARTEMIS) Three recent GRBs (blue dots) emitted high-energy gamma-ray and X-ray light over time spans up to 100 times greater than typical long bursts and constitute a new ultra-long class. This plot compares the energy received and the event duration among different classes of transient high-energy events: long GRBs (green); the disruption of an asteroid or comet by a neutron star or stellar-mass black hole in our own galaxy, or the break-out of a supernova shock wave in another galaxy (orange); and the tidal disruption of a star by a supermassive black hole in another galaxy (purple). Unlabeled. Credit: NASA's Goddard Space Flight Center, after B. Gendre (ASDC/INAF-OAR/ARTEMIS) The number, duration and burst class for GRBs observed by Swift are shown in this plot. Colors link each GRB class to illustrations above the plot, which shows the estimated sizes of the source stars. For comparison, the yellow star is about 20 percent larger than our Sun. Credit: Andrew Levan, Univ. of Warwick GRB 111209A exploded on Dec. 9, 2011. The blast produced high-energy emission for an astonishing seven hours, earning a record as the longest-duration GRB ever observed. This false-color image shows the event as captured by the X-ray Telescope aboard NASA's Swift satellite. Credit: NASA/Swift/B. Gendre (ASDC/INAF-OAR/ARTEMIS) Artist's impression of blue supergiant star during gamma-ray burst.Credit: CNRS/C Three unusually long-lasting stellar explosions discovered by NASA's Swift satellite represent a previously unrecognized class of gamma-ray bursts (GRBs). Two international teams of astronomers studying these events conclude that they likely arose from the catastrophic death of supergiant stars hundreds of times larger than the sun. GRBs are the most luminous and mysterious explosions in the universe. The blasts emit surges of gamma rays — the most powerful form of light — as well as X-rays, and they produce afterglows that can be observed at optical and radio energies. Swift, Fermi and other spacecraft detect an average of about one GRB each day.Traditionally, astronomers have recognized two GRB types, short and long, based on the duration of the gamma-ray signal. Short bursts last two seconds or less and are thought to represent a merger of compact objects in a binary system, with the most likely suspects being neutron stars and black holes. Long GRBs may last anywhere from several seconds to several minutes, with typical durations falling between 20 and 50 seconds. These events are thought to be associated with the collapse of a star several times the sun's mass and the resulting birth of a new black hole. Both scenarios give rise to powerful jets that propel matter at nearly the speed of light in opposite directions. As they interact with matter in and around the star, the jets produce a spike of high-energy light. A detailed study of GRB 111209A, which erupted on Dec. 9, 2011, and continued to produce high-energy emission for an astonishing seven hours, making it by far the longest-duration GRB ever recorded.Another event, GRB 101225A, exploded on Christmas Day in 2010 and produced high-energy emission for at least two hours. Subsequently nicknamed the "Christmas burst," the event's distance was unknown, which led two teams to arrive at radically different physical interpretations. One group concluded the blast was caused by an asteroid or comet falling onto a neutron star within our own galaxy. Another team determined that the burst was the outcome of a merger event in an exotic binary system located some 3.5 billion light-years away.Using the Gemini North Telescope in Hawaii, a team led by Andrew Levan at the University of Warwick in Coventry, England, obtained a spectrum of the faint galaxy that hosted the Christmas burst. This enabled the scientists to identify emission lines of oxygen and hydrogen and determine how much these lines were displaced to lower energies compared to their appearance in a laboratory. This difference, known to astronomers as a redshift, places the burst some 7 billion light-years away. Levan and his colleagues also examined 111209A and the more recent burst 121027A, which exploded on Oct. 27, 2012. All show similar X-ray, ultraviolet and optical emission and all arose from the central regions of compact galaxies that were actively forming stars. The astronomers conclude that all three GRBs constitute a hitherto unrecognized group of "ultra-long" bursts.To account for the normal class of long GRBs, astronomers envision a star similar to the size sun's size but with many times its mass. The mass must be high enough for the star to undergo an energy crisis, with its core ultimately running out of fuel and collapsing under its own weight to form a black hole. Some of the matter falling onto the nascent black hole becomes redirected into powerful jets that drill through the star, creating the gamma-ray spike, but because this burst is short-lived, the star must be comparatively small. Because ultra-long GRBs persist for periods up to 100 times greater than long GRBs, they require a stellar source of correspondingly greater physical size. Both groups suggest that the likely candidate is a supergiant, a star with about 20 times the sun's mass that still retains its deep hydrogen atmosphere, making it hundreds of times the sun's diameter.Watch this video on YouTube. For More InformationSee [http://www.nasa.gov/mission_pages/swift/bursts/supergiant-stars.html](http://www.nasa.gov/mission_pages/swift/bursts/supergiant-stars.html) Related pages