Probing the Early Universe with Extremely Energetic Gamma-Ray
Bursts
Dieter Hartmann (Clemson)
The Gamma-Ray Burst phenomenon was discovered in the late sixties and
announced in the early seventies. After many decades of confusion
about the nature of this transient phenomenon, NASA’s
Compton Gamma Ray Observatory (1991-2000) advanced our understanding
to the point that their Galactic origin became less and less
viable. It was the keen X-ray eyes of the Italian-Dutch BeppoSAX
satellite that in 1997 caught the first X-ray afterglow of a burst,
which in turn also led to the discovery of optical emission following
the brief flare in the gamma-band. This allowed astronomers to
establish their distances, and to their amazement they turned out to
be very distant, cosmological sources – where one uses
redshifts instead of lightyears as a measure of their distance. Their
large apparent brightness and the large distances imply enormous
energies, which for a while challenged our theoreticians. In the past
years a better understanding of the GRB-phenomenon has emerged,
linking these transients to the final, violent moments of exploding,
massive stars and the merging of exotic binary systems of compact
stars, such as two neutron stars or a neutron star and a black
hole. The processes that take place when black holes form in these
events provide a laboratory for the exploration of ultra-relativistic
physics, and their afterglow emissions can be used to probe the
processes of star formation and chemical evolution in the earliest
proto-galactic structures that emerged from the big bang. When we
observe a gamma-ray burst at a very large distance, we may be looking
at the death-cry of one of the first stars ever born in the
universe. With NASA’s Swift satellite (2004 - ), dedicated
to the study of this phenomenon, we are currently witnessing these
bursts twice a week, and with future missions on the drawing boards we
may be able to follow up on one burst every day. I will describe the
history of GRB studies and give an outlook on how we will use these
explosive events to study the beginnings of galaxy formation in the
early universe.
