Gamma-Ray Bursts – University of Copenhagen

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Gamma-ray bursts (GRBs) are bursts of radiation in the gamma-ray part of the electromagnetic spectrum with typical energies more than thousand times higher than for visible light.

They last from fractions of a second to hundreds of seconds and occur at a rate of about 1 per day in the Universe from random directions in the sky. The received energies at the Earth can be quite substantial, sometimes causing ionization of the outer atmosphere. There seems to be at least two classes of GRBs; a class of short GRBs lasting less than about 2 s and a class of long GRBs lasting longer than about 2 s.

In 1997 it was established that the long GRBs originate from very large distances in galaxies at cosmological distances. Since then we have learned, partly thanks to research carried out at DARK, that the long GRBs are most likely caused by very massive stars that collapse after having consumed all their nuclear fuel. The GRBs are produced when a black hole is formed during the collapse. The short GRBs also occur in distant galaxies, but the exact origin of these bursts is not yet clarified.

At the Dark Cosmology Centre we use GRBs to probe the nature of the galaxies hosting GRBs as a means to probe star formation throughout cosmic history. In particular, we are interested in studying the very first stars and galaxies that formed at the end of the dark ages of the Universe. We are also aiming at better understanding of the physics of GRB formation, including how short GRBs, long GRBs, and supernovae fit into a broader picture of stellar death.