For the first time computer simulations by the Max
Planck Institute for Gravitational Physics predict what astronomers
will "see" with gravitational wave telescopes during the collision
of two black holes.

The merging of two black holes is one of the strangest
occurrences expected in modern astronomy. Now physicists using the world’s
biggest computers have shown astronomers what to look for and have brought
the first observations of these events much closer.

In a paper that is to appear in Physical Review Letters on Sept. 17,
2001, a team of young researchers at the Max Planck Institute for Gravitational
Physics (Albert Einstein Institute in Golm, near Potsdam and Berlin,
Germany) has predicted the gravitational waves that should be emitted
when black holes plunge towards each other and merge. The team consists
of John Baker (now at NASA’s Goddard Space Flight Center in the USA),
Bernd Brügmann, Manuela Campanelli, Carlos Lousto, and Ryoji Takahashi.
They call themselves the Lazarus Team.

The most important result of the Lazarus simulations will be to provide
gravitational wave astronomers with a set of templates which they can
use to recognize the signals in the noise at the output of their detectors.
The Lazarus simulations make predictions that are more detailed and
more reliable than any before. The Lazarus scientists expect the gravitational
waves to be stronger than previously accepted estimates.

Bernard Schutz, one of the directors of the Max Planck Institute for
Gravitational Physics, observes: "The success of the Lazarus Project
at the AEI comes at just the right time. Black hole mergers could provide
the first-ever detections, which will be a landmark for Einstein’s theory
of general relativity. Numerically computed gravitational wave-forms
will not only help us to detect and recognize waves from these events,
but will help us to deduce from the observations the masses of the holes
and their distance from us. Black hole mergers emit no light, radio
waves, or X-rays. We can only detect them by catching their gravitational

Previous simulations have not been able to follow the black holes through
the whole merger event. Deep inside a black hole lurks a "singularity",
a place where gravity gets huge. Computer simulations have had difficulty
modelling the waves outside the hole at the same time as the inside.

The key advance by the Lazarus team at the AEI came when they combined
two approaches, full numerical simulation for the essentially strong-field
regime of the collision and an approximation method, perturbation theory,
for computing the radiation from the resulting distorted single black
hole. They cut off the full simulation before it went bad, and then
used a different method that looked only at the gravitational waves
outside the merged hole. Computers again had to calculate this radiation,
but they could avoid the problems caused by looking inside the holes.


Shown are computer-generated images that represent the invisible
gravitational waves racing outwards towards earth after the collision
of two black holes. The waves start localized near the center of the
collision, build up to spherical looking shells of radiation and eventually
leave the cube that bounds the computer visualization.

Visualization: W. Benger (Konrad-Zuse-Zentrum
für Informationstechnik Berlin (ZIB), Max-Planck-Institut für
Gravitationsphysik (Albert-Einstein-Institut, AEI))



Original paper::
Waveforms from Inspiralling Binary Black Holes

J. Baker, B. Brügmann, M. Campanelli, C. O. Lousto, and R. Takahashi

Physical Review Letters 17 September 2001 (Published 31 August 2001)

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