A large step closer to the first direct detection of gravitational waves

May 19th 2015

Albert Einstein Institute researchers make key contributions to advanced LIGO gravitational-wave detectors

When black holes merge strong gravitational waves are emitted. The graph shows a state-of-the-art comparison between waveforms of a black hole binary calculated according to two different techniques (top panel); the lower panel shows the final few cycles, including the merger of the two black holes.
© UMD/AEI/Milde Marketing/ESO/NASA

The gravitational-wave observatory GEO600 is located in Ruthe near Sarstedt, 20 kilometers south of Hannover. It is a laser interferometer with 600 meter long arms used by AEI scientists to search for the tiny space-time ripples predicted by Albert Einstein.
© Harald Lück/AEI

Atlas at the AEI in Hannover ist the worldwide most powerful computercluster dedicated to gravitational-wave data analysis.
© Massimo Fiorito/AEI

On May 19, the LIGO Scientific Collaboration (LSC) will dedicate their second-generation gravitational-wave detectors (aLIGO) in a ceremony at the Hanford detector site. Researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover and Potsdam, Germany, have made significant contributions in several key areas: custom-made high-power laser systems required for the high-precision measurements, efficient data analysis methods running on powerful computer clusters, and accurate waveform models to detect gravitational waves and extract astrophysical information. The AEI is a leading partner in the international gravitational-wave science community, and its researchers keep pushing the boundaries of science on the way to the first direct detection of gravitational waves.

This will open a new window to the otherwise invisible “dark” side of the Universe and mark the beginning of gravitational-wave astronomy. Gravitational waves are ripples in space-time that are emitted by cataclysmic cosmic events such as exploding stars, merging black holes and/or neutron stars, and rapidly rotating compact stellar remnants. These waves were predicted in 1916 by Albert Einstein as a consequence of his general theory of relativity, but have never been observed directly. At their design sensitivity, the aLIGO instruments should detect multiple gravitational-wave events each year.

GEO600 contributes advanced detector techniques
Researchers at the AEI together with the Laser Zentrum Hannover developed and installed the high-power laser systems used in the aLIGO detectors. “With our UK colleagues we designed and operate the gravitational-wave detector GEO600. We use it as a think tank and testbed for advanced detector techniques,” says AEI director Prof. Karsten Danzmann, who is also the director of the Institute for Gravitational Physics at the Leibniz Universität Hannover. “Many of these new methods are now in use at the aLIGO detectors, such as signal recycling and monolithic mirror suspensions.” Danzmann's AEI division plays a pioneering role in the development and application of non-classical light in gravitational-wave detectors. GEO600 is the only detector worldwide using squeezed light to improve the detector sensitivity beyond limits set by the quantum nature of light.

Leading partner in data analysis with powerful supercomputers
AEI scientists develop and implement advanced and efficient data analysis methods to search for weak gravitational-wave signals in the aLIGO detector data streams. “The AEI is a leading partner in the global joint data analysis efforts of the LSC,” says Prof. Bruce Allen, director at the AEI. “For this purpose we operate Atlas, the most powerful computer cluster in the world designed for gravitational-wave data analysis.” During the first data-taking run in late 2015, Allen's division will search through the data on the Atlas cluster. Together with US partners the division also operates Einstein@Home, a global volunteer distributed computing project for gravitational-wave data analysis. Almost 400,000 volunteers from all over the world have contributed computing time over the past decade on their home PCs, laptops, or smartphones.

Developing accurate waveform models and searches of merging black holes
“We have developed the most accurate waveform models so far of merging black holes. Together with our LSC colleagues we will conduct a search for those signals in the aLIGO data using the Atlas cluster. Gravitational-wave observations of these systems will give us completely new insights into these otherwise invisible objects,” says Prof. Alessandra Buonanno, director at the AEI in Potsdam. “The new search is the first to include the effects of the black-holes' spins, which will improve its sensitivity and thereby our chances of detection.” AEI scientists, in collaboration with LSC colleagues, have also prepared a follow-up analysis for the first observation run in late 2015 that will infer astrophysical parameters of the merging black holes.

Next step: First observation run
aLIGO will start its first data-taking (observation) run “O1” in the autumn of 2015, bringing the era of gravitational-wave astronomy a large step closer to reality – with key contributions from the Albert Einstein Institute.