Aug. 31, 2006 — Following up on an unusual gamma ray burst, scientists have for the first time caught sight of a giant star in its death throes.
The explosions, called supernovas, happen when massive stars run out of material for nuclear reactions in their cores and collapse in on themselves due to gravitational forces. Typically, a supernova cannot be found until days after the explosion, when debris starts to clear and energy in optical wavelengths becomes visible.
But thanks to quick and innovative detective work, scientists were on the scene, relatively speaking, during the death of a star 440 million light years away in the constellation Aries.
"Such details have never been revealed so early and so clearly," said Neil Gehrels, the principal investigator for the Swift telescope, managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The Swift telescope operates from space as a satellite, and was key to finding the explosion.
Swift pinpoints the location of high-energy bursts in the cosmos, allowing other observatories, such as the Hubble Space Telescope and the Compton Gamma Ray Observatory to conduct detailed studies.
The clues leading to astronomers' first real-time supernova viewing began Feb. 18 when Swift picked up an unusual burst of energy 25 times closer and 100 times longer than the typical gamma ray burst. The burst lasted nearly 40 minutes, while most gamma ray bursts are over in seconds.
The burst also was about 100 times less energetic than typical gamma ray bursts and more of its energy was released as X-rays rather than gamma rays.
Using a combination of ground- and space-based instruments, astronomers now believe Swift detected a jet of high-energy X-rays, which pierced the core of the doomed star minutes before it burst apart. The event is described in four papers published in this week's issue of Nature.
"This (gamma ray burst) was the most extraordinary evolving object yet seen by Swift," said Paul O'Brien, with the U.K.'s University of Leicester.
The observations began with three instruments aboard Swift itself which collected data as the star exploded. A team lead by Sergio Campana of the Italian National Institute for Astrophysics in Milan traced X-ray emissions that faded to ultraviolet and finally optical light as the shock wave from the explosion forced remnants of the star out into the surrounding dust.
Debris from the star remains under analysis. Some scientists are recommending a new classification for the supernova, which, rather than forming a black hole, is believed to have left behind a highly magnetic type of neutron star called a magnetar.
"Usually these events are not detected until after the supernova has brightened substantially in the optical wavelength, many days after the initial explosion," said Keith Mason, a Swift lead investigator. "On this occasion we were able to study the remarkable event in all its glory from the very beginning."
