M.
Camenzind (Heidelberg):
Black Holes in the Universe
Abstract:
While physicists
have been grappling with the theory of black holes (BH),
as shown by the many contributions to the Einstein year,
astronomers have been successfully searching for real
black holes in the Universe. Black hole astrophysics
began in the 1960s with the discovery of quasars and
other active galactic nuclei (AGN) in distant galaxies.
Already in the 1960s it became clear that the most natural
explanation for the quasar activity is the release of
gravitational energy through accretion of gas onto supermassive
black holes. The remnants of this activity have now
been found in the centers of about 50 nearby galaxies.
BH astrophysics received a new twist in the 1970s with
the discovery of the X-ray binary (XRB) Cygnus X-1.
The X-ray emitting compact object was too massive to
be explained by a neutron star. Today, about 20 excellent
BH candidates are known in XRBs. On the extragalactic
scale, more than 100.000 quasars have been found in
large galaxy surveys. At the redshift of the most distant
ones, the Universe was younger than one billion year.
The most enigmatic black hole candidates identified
in the last years are the comapct objects behind the
Gamma-Ray Bursters. The formation of all these types
of black holes is accompanied by extensive emission
of gravitational waves. The detection of these strong
gravity events is one of the biggest challenges for
physicists in the near future.
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