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EINBLICKE
27
Stars have something fascinating about them. They stand
apparently immutable in the firmament, while the Earth orbits
the Sun. But stars are finite too. They come into being and go
through a process of development that ends in their death
when the nuclear fusion at their centre is extinguished. The
heavier a star, the faster it burns out, and themore dramatic its
end. In those stars with the largest mass, gravity brings about
a collapse that is utterly unstoppable. A black hole is born.
Besides these so-called stellar black holes, which weigh about
as much as the stars,
supermassive black
holes also exist at the
centre of galaxies.
Their mass is greater than our sun by many orders of magnitu-
de. At the centre of theMilkyWay in the Sagittarius constellati-
on is a giant black holewhosemass is 4million times that of the
Sun. It was discovered in the 1990s through the movement of
the stars around the X-ray emitter Sagittarius A*. Stars revolve
around the central black hole much like planets around a sun,
providing information about the central mass which attracts
them. It is assumed that at the centre of other galaxies black
holes that aremuch heavier exist, in which several billion solar
masses have converged.
The existence of black holes is inferred by Einstein's field equat-
ions of general relativity. Black holes are described by both the
Schwarzschild solution and the Kerr metric. Back in 1916 –the
year inwhich the general theory of relativitywas first published
–
the astronomer Karl Schwarzschild described the simplest
black hole in theory. It is spherically symmetric and – like all
black holes – has an event horizon beyond which nothing
can escape the gravitational pull. An event horizon can be
pictured as a membrane which is permeable in one direction
only. Light and particles can fall through this threshold into the
black hole, but they can never escape again to the outer parts
of the universe fromwhich they came. Thus the event horizon
also forms a border for all forms of communication. If a person
were to cross the horizon he or she would never again be able
to communicate with anything on the other side.
The event horizon forms a border
for all kinds of communication.
Die Autoren
The Authors
Prof. Dr. Jutta Kunz ist seit 1993 Hochschullehrerin für Feldtheorie
in Oldenburg. Sie studierte Physik in Gießen und Seattle (USA).
Nach ihrer Promotion in Gießen arbeitete sie am Los Alamons
National Laboratory in New Mexico (USA). Anschließend lehrte sie
an der Universität Gießen und forschte am Nationaal Instituut Voor
Subatomaire Fysica in Amsterdam und an der Universität Utrecht
(
Niederlande). 1989 habilitierte sich Kunz in Oldenburg.
Prof. Dr. Jutta Kunz became Professor for Field Theory at the Uni-
versity of Oldenburg in 1993. She studied physics in Gießen and
Seattle (USA). After receiving her PhD in Gießen, Kunz worked at
the Los Alamons National Laboratory in New Mexico (USA). After-
wards she taught at the University of Gießen and did research at
the Nationaal Instituut Voor Subatomaire Fysica in Amsterdam and
at the University of Utrecht (Netherlands). In 1989 she habilitated
in Oldenburg.
Prof. Dr. Claus Lämmerzahl, kommissarischer Leiter des Zentrums für
angewandte Raumfahrttechnologie und Mikrogravitation (ZARM)
der Universität Bremen, studierte, promovierte und habilitierte sich in
Konstanz. Der Physiker war Post-Doc inParis (Frankreich) und leitet seit
2003
die Arbeitsgruppe „Fundamental Physics“ am ZARM. Seit 2004
lehrt er am Institut für Physik der Universität Oldenburg. Lämmerzahl
ist Vorsitzender des Verbands „Gravitation und Relativitätstheorie“.
Prof. Dr. Claus Lämmerzahl is acting director at the Center of Ap-
plied Space Technology and Microgravity (ZARM) at the University
of Bremen. He obtained his degree, doctorate and habilitation in
Constance. The Physicist worked as a post-doc in Paris (France) and
has been at ZARM since 2003, where he heads the research group
on “Fundamental Physics”. He has taught at the Institute of Physics
at the University of Oldenburg since 2004. Lämmerzahl is chairman
of the association for “Gravity and Relativity Theory”.
