© NASAArtist's illustration of one model of the bright gamma-ray burst GRB 080319B.
Detectable for only a few seconds but possessing enormous energy, gamma-ray bursts are difficult to capture because their energy does not penetrate the Earth's atmosphere. Now, thanks to an orbiting telescope, astrophysicists are filling in the unknowns surrounding these bursts and uncovering new questions.
The Fermi Gamma-Ray Space Telescope, formerly called the Gamma-Ray Large Area Space Telescope, launched on June 11, 2008. As part of its mission, the telescope records any gamma-ray bursts within its viewing area.
"Fermi is lucky to measure the highest energy portion of the gamma-ray burst emission, which last for hundreds to thousands of seconds -- maybe 20 minutes," said Péter Mészáros, Eberly Chair Professor of Astronomy and Astrophysics and Physics, Penn State.
Most gamma-ray bursts occur when stars that are more than 25 times larger than our sun come to the end of their lives. When the internal nuclear reaction in these stars ends, the star collapses in on itself and forms a black hole. The outer envelope of the star is ejected forming a supernova.
"The black hole is rotating rapidly and as it is swallowing the matter from the star, the rotation ejects a jet of material through the supernova envelope," said Mészáros.
This jet causes the gamma-ray burst, which briefly becomes the brightest thing in the sky. However, unlike supernovas that radiate in all directions, gamma-ray bursts radiate in a very narrow area, and Fermi sees only jets ejecting in its direction. This, however, is the direction in which they send their highest energy photons. Any gamma-ray bursts on the other side of the black hole or even off at an angle are invisible to the telescope.
