The two jets pierce the outer shell of the dying star. A black hole has already formed in its interior. After just a few seconds, the jets will only start to have short-lasting gamma-ray flashes. The light from the afterglow lasting several weeks was analyzed by the astronomers. (Source: Max Planck Institute for Extraterrestrial Physics)
Read out Gamma-ray flashes are considered the most powerful explosions in the universe since the Big Bang. While in an atomic bomb explosion only about one gram of matter is converted into energy, in these flashes it is more than a thousand earth masses. Observations of a gamma-ray flash on March 29, 2003, now provide astronomers with a better understanding of the processes involved in these explosions. Jochen Greiner from the Max Planck Institute for Extraterrestrial Physics in Garching and his colleagues present their findings in the journal Nature (vol. 426, p. 157). The gamma-ray flash GRB 030329 is the next ever observed. He had a distance of "only" 2.6 billion light years. By comparison, our sun is about eight light minutes or 150 million kilometers from Earth. Because of this "small" distance was the afterglow? the afterglow? of only a few seconds lasting gamma-ray flash particularly bright.

The actual lightning had been discovered by Nasa satellite Hete-2. The group around Greiner observed with the Very Large Telescope of the European Southern Observatory for several weeks, the afterglow of lightning and could gain some valuable information from the data obtained.

The astronomers were able to prove that the light of the afterglow is polarized with a strength of one to three percent. In polarized light, the electric field vector of the light does not oscillate indiscriminately in all directions, but in a preferred plane along the direction of propagation. The light reflected by a shop window, for example, is polarized.

This polarization was predicted by the theory that events around a gamma-ray flash are as follows: the center of a dying star collapses into a black hole. The massive amount of energy released in the process is transported outwards in two oppositely directed jets. display

After a few seconds these jets pierce the still existing outer shell of the star and tear it. The star becomes a supernova. The jets produce the gamma-ray flashes. In the interstellar medium consisting of thinly distributed dust and gas, the jets are decelerated. This creates the afterglow.

However, not all observations can be explained with the previous theory. The polarization in the light of the afterglow constantly changes its strength and direction. Greiner and colleagues speculate that possibly two pairs of jet may be generated. The faster pair would produce the gamma-ray flashes, and the slower but more energetic pair would only dominate the observed light after a few days, as the faster jet pair slowed down enough.

Further information and pictures about GRB 030329 can be found here.

Axel Tilleman

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