November 21, 2013
Powerful Gamma-Ray Burst Detected Close To Milky Way
[ Watch the Video: Overview Animation of Gamma-ray Burst ]
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers from around the world have compiled data from satellites and observatories to help explain the most powerful gamma-ray burst ever recorded, according to a study published in the journal Science.
Led by researchers from the Niels Bohr Institute and the University of Leicester, the international team said this gamma-ray burst occurred relatively close to the Milky Way. Gamma-ray bursts (GRBs) are violent bursts of gamma radiation typically associated with an exploding massive star.
When a star explodes as a supernova it releases the gamma-ray bursts, which are so bright that they can be seen from across the universe. Telescopes underneath Earth’s atmosphere are unable to detect this light, however; so astronomers rely on space-based observatories such as the Swift satellite to pick up on them.
Swift monitors the skies and typically discovers about 100 gamma-ray bursts each year, but the one they found this past April was particularly unusual.
"We suddenly saw a gamma-ray burst that was extremely bright – a monster gamma-ray burst. This one of the most powerful gamma-ray bursts we have ever observed with the Swift satellite," astrophysicist Daniele Malesani, Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen said in a statement.
As soon as the gamma-ray burst was spotted, the satellite directed its instruments to measure X-rays, ultraviolet radiation and optical light in the visible field. All of this happens quickly, because the gamma-ray burst is over in under a minute.
"We follow the so-called afterglow, which usually lasts a few days or for several weeks, from both Swift and from the ground-based telescopes. In this case, the burst was so powerful that we could observe the afterglow for several months,” Malesani said. “By analyzing the light from the afterglow, we can study its spectral composition, which can tell us about the properties of the original star.”
The team discovered that this burst came from a giant star that is 20 to 30 times the mass of our Sun. However, Malesani said that the star’s actual size is only three to four times that of the Sun, so it is extremely compact. They have localized the star in a galaxy that is relatively near, saying the light took just 3.75 billion years to reach us on Earth.
"We normally detect GRBs at great distance, meaning they usually appear quite faint. In this case the burst happened only a quarter of the way across the Universe meaning it was very bright. On this occasion, a powerful supernova was also produced, something we have not recorded before alongside a powerful GRB and we will now be seeking to understand this occurrence,” Professor Paul O'Brien of the University of Leicester's Department of Physics and Astronomy said in a statement.
Studying the behavior of gamma-ray bursts enables scientists to test the laws of physics. Researchers were able to use Swift’s observations to discover many new and unexpected aspects of this cosmic event. Professor Julian Osborne, Swift team leader at the University of Leicester's Department of Physics and Astronomy, said this very bright burst reassures scientists that they are on the right track in understanding such explosions.
"Seeing such a bright flash a quarter of the way across the observable universe really brings home the astonishing power of these explosions,” added Professor Nial Tanvir, also of the University of Leicester's Department of Physics and Astronomy.
Image Below: In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the black hole, collisions within the jet, and from the jet's interaction with its surroundings. Credit: NASA's Goddard Space Flight Center