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Gravitational Wave Astronomy

Methods - Sources - Observation

Gravitational Wave Astronomy stands for the ambitious scientific endeavor to extend our current astronomy, which is largely based on the analysis of electromagnetic waves, by including gravitational wave signals as sources of information about the universe, thereby utilizing one more of the fundamental interactions for astronomical observation. This new window onto the universe will soon contribute in a significant and unique manner to our understanding of such important astrophysical phenomena as black hole collisions, neutron star dynamics, and super nova explosions, making many of the involved physical processes accessible to scientific analysis for the very first time.

The focus of the SFB/TR7 was the theoretical and experimental investigation of gravitational waves and their astrophysical sources, which is a topic of Einstein's theory of gravitation, general relativity, which has been highly successful in its applications in astrophysics, astronomy, cosmology and celestial mechanics, and which for example has already found its way into every day technology through the Global Positioning System (GPS).

Gravitational waves are not just a theoretical concept but a phenomenon confirmed by astronomical observation. The analysis of the radio signals of the binary pulsar PSR 1913+16 allows to compute the decrease of distance between the two stars in this binary, as well as the corresponding loss of energy of the system. This loss of energy agrees very accurately with the prediction of Einstein's theory for the loss of energy through the emission of gravitational waves in a binary system.

The direct measurement of the gravitational wave signals poses an extreme challenge for experimental physics, and so far detection of gravitational waves has not been achieved. However, there is every indication that the large laser interferometers LIGO (USA), VIRGO (Italy/France), GEO600 (Germany/Great Britain), and TAMA (Japan) will rather soon, probably within the next four to six years, detect gravitational waves. On the horizon in 2015 there is the space based detector LISA, which will open up an additional frequency range in the spectrum of gravitational waves.

The SFB/TR7 played a leading international role in the great theoretical efforts that necessarily have to accompany the work on the detectors. The experiments made use of the theoretical predictions for the gravitational wave forms to guide the search for signals in the detector noise, and each potential source of gravitational radiation, say the merger of black holes or the inspiral of compact binaries, requires its own physical model to make predictions possible. Anticipating detection, methods were being prepared to extract information about the astrophysical origin of the gravitational waves, allowing insight into the physical processes at the source. Source modelling and signal analysis required the close collaboration of theoretical and experimental physicists, and the scope of this task established the necessity of an efficient scientific community in addition to detector construction and operation.

The SFB/TR7 developed and supported the scientific community around detectors like GEO600 and LISA through a complete range of projects in detector physics, data analysis, theoretical predictions of gravitational waves, and their astrophysical interpretation. It was essential for the SFB/TR7 that K. Danzmann (Hannover) and B. Schutz (Potsdam) played key roles in the international gravitational wave detector community around GEO600 and LISA.

The collaboration of 80 scientists (about 50 principal investigators and staff, about 25 positions DFG funded) had a very positive effect on the education of young researchers in Germany. The German universities were enabled to educate the future leaders in this attractive and highly promising area of gravitational physics and relativistic astrophysics.

Working jointly towards the grand goal of gravitational wave astronomy were experimental and theoretical physicists, astrophysicists and mathematicians from the universities of Jena, Tübingen and Hannover as well as from the Max Planck Institutes for Gravitational Physics in Potsdam and for Astrophysics in Garching.