A new model attempts to explain long Gamma-Ray Bursts

September 18, 2009 14:16 by scibuff

Gamma-ray Bursts (GRBs) are the most powerful explosions in the universe. In a few seconds they release a tremendous amount of energy outshining billions of stars. They were first discovered (accidentally) in 1967 by satellites designed to detect tests of nuclear weapons. Although we detect new GRBs on daily basis, no one knows the exactly the process behind their origin.

The most-widely accepted model proposes that GRBs are created in a gravitational collapse of extremely massive stars into black holes when matter in the accretion disk is heated by neutrinos and driven into narrowly focused jets along the rotational axis.

As the core of a massive star in a distant galaxy collapses, deep inside, twin beams of matter and energy begin to blast their way outward. Within seconds, the beams have eaten their way out of the star, and observers at Earth see it as a gamma-ray burst, GRB 060729A - Credit for caption: Phil Plait SSU NASA E/PO; Images: Aurore Simonnet SSU NASA E/PO

As the core of a massive star in a distant galaxy collapses, deep inside, twin beams of matter and energy begin to blast their way outward. Within seconds, the beams have eaten their way out of the star, and observers at Earth see it as a gamma-ray burst, GRB 060729A - Credit for caption: Phil Plait SSU NASA E/PO; Images: Aurore Simonnet SSU NASA E/PO

Nevertheless, this model makes it difficult to explain long GRBs with the duration of more than 100 seconds and cannot account for afterglows lasting up to 10,000 observed by the Swift spacecraft.

Professor Komissarov and his colleagues at the University of Leeds accredit the creation of the matter jets to a magnetic mechanism and examine the close binary scenario involving a merger or a WR star (evolved, massive star of over 20 solar masses) with a neutron star or a black hole, in their article Close Binary Progenitors of Long Gamma Ray Bursts.

“The neutrino model cannot explain very long gamma ray bursts and the Swift observations, as the rate at which the black hole swallows the star becomes rather low quite quickly, rendering the neutrino mechanism inefficient, but the magnetic mechanism can.”

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