Exploring the mystery of black holes and testing general relativity

Scientists in Potsdam prepare for fast and targeted data evaluation for the LISA space observatory

An interdisciplinary and international team of experts is currently preparing at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam-Golm for the evaluation of data to be supplied by the LISA space observatory.

With LISA (Laser Interferometer Space Antenna), a joint project of ESA and NASA, it will be possible for the first time to determine the gravity around a black hole, to map the space-time surrounding the black hole and thus to subject general relativity to a rigorous test.

AEI scientists are leading the LISA mission from both the theoretical and the experimental side:

• Prof. Dr. Bernard F. Schutz, Director at AEI, in the field of theoretical astrophysics and data analysis
• Prof. Dr. Karsten Danzmann, Director at the Hanover branch of the AEI, is in charge of the European side of the LISA mission

Background

For decades, scientists have been amazed that such gigantic phenomena as black holes can be described by only two quantities: their mass and their rotational speed. Although they absorb anything that comes too close to them because of the strong gravitation in their environment, they do not reveal any information about the whereabouts of the “swallowed” matter or about their own history. So far, mass and rotational speed remain the only features that characterize a black hole. Nobel Prize winner Subramaniam Chandrashekhar once remarked that nothing surprised him more than the fact that such gigantic phenomena in the universe can be described by only two quantities.

Now, for the first time, there is a promising way to learn more about black holes and the gravitation in their vicinity, while at the same time subjecting general relativity to a rigorous test: By observing small objects and their irregular and complicated orbits around a black hole From the characteristic gravitational waves that are generated, scientists can draw conclusions about the exact course of the orbit, the continuous approach to the black hole and the distribution of gravity around the black hole.

LISA, the laser interferometer in space, will be able to observe such gravitational waves from 2015 onwards. Under the leadership of AEI scientists, preparations are therefore already underway worldwide to analyze the data that LISA will transmit to Earth.

LISA

LISA will consist of three satellites arranged in the shape of an isosceles triangle, each connected by laser beams over a distance of 5 million kilometers. The development of the LISA technology is progressing in giant strides and will be tested in space with the LISA Pathfinder Mission starting in 2009.

Black holes 

Seen from the outside, a black hole is not a tangible object, but a region of space into which matter falls from the outside, but from which nothing can escape. The border between this region and the rest of the universe is called the event horizon. Black holes exert a strong gravitational influence on their surroundings: For example, they deflect the orbits of nearby stars or pull the gas of nearby stars towards them.