Max Planck Institute for Gravitational Physics (Hanover)

Eclipses of five special pulsars help to identify the pulsar’s masses.

MeerKAT discovers cosmic lighthouses with unusual properties

What is needed to distinguish between binary black hole and neutron star black hole mergers?

Results from joint Japanese-German gravitational-wave observing run

It should not actually exist - a black hole with a mass 85 times that of our sun. But that is precisely what astronomers have discovered. Apparently, this heavyweight used to be part of a binary star system before it merged with its equally massive partner. The resulting space-time quake unleashed gravitational waves that are posing many a puzzle for researchers at the Max Planck Institute for Gravitational Physics in Potsdam and Hanover.

Humankind has always been fascinated by the mythical concept of a cyclic universe that ends in a cosmic conflagration and is then reborn. Modern Big Bang theory that suggests an infinitely expanding universe rules out this possibility. But has the final word been spoken on the issue? Anna Ijjas investigates this fundamental question at the Max Planck Institute for Gravitational Physics in Hannover.

The Einstein@Home project makes it possible for anyone to search for gravitational waves on their own PC, laptop or smartphone and thus become scientific explorer themselves. Bruce Allen, Director at the Max Planck Institute for Gravitational Physics in Hannover, is the founder of this citizen science project. The software is now also used to track down pulsars in big data. Researchers from the Max Planck Institute for Radio Astronomy in Bonn are also involved in this search.

Albert Einstein was right: gravitational waves really do exist. They were detected on September 14, 2015. This, on the other hand, would have surprised Einstein, as he believed they were too weak to ever be measured. The researchers were therefore all the more delighted - particularly those at the Max Planck Institute for Gravitational Physics, which played a major role in the discovery.

… is not at all where the researchers from the Max Planck Institute for Gravitational Physics want to be. The issue at hand is nothing less than the base of one of the pillars of our modern world view, the theory of general relativity. In 1915, Albert Einstein formulated, among other things, the theory that the accelerated movement of masses causes disturbances that move through space at the speed of light. He called these disturbances gravitational waves. The Earth, for instance, creates a bulge in space-time on its annual orbit around the Sun, emitting gravitational waves in the process. Given the enormous number of planets and binary stars, space must be utterly teeming with these waves. In most cases, however, the cosmic ripples are too weak to be detected with terrestrial detectors. Fortunately, there are far stronger tremors in the universe: the dance or collision of neutron stars with black holes, or the explosion of a massive sun into a supernova. Such violent events are what scientists around the world are waiting for – for example out in a field in Ruthe, near Hanover. This is where GEO600 stretches out its two 600-meter-long arms. The evacuated stainless steel tubes measure 60 centimeters in diameter and are corrugated to increase their stability. They house the second-longest laser beam interferometer in Europe. The measuring principle is based on the fact that gravitational waves alternately compress and stretch space. If they speed through GEO600, they will also change the paths of the laser beam that runs through the two perpendicularly arranged tubes. This tiny length difference on the order of 10-19 meters causes the light waves in the detector to fall out of step. A signal appears. Alarm! To date, however, there have been only test alarms. The researchers are working on continuously increasing the system’s sensitivity. When the cosmos quakes again, they want to finally capture the gravitational waves and thus open up a new window into space.

The mystery of a gamma-ray source known for two decades has finally been solved. An extremely rapidly rotating neutron star in a binary system is the source of the gamma rays. For this discovery, 10 years of gamma-ray data from NASA’s Fermi Gamma-ray Space Telescope has been analysed, using the distributed volunteer computing project Einstein@Home. The thorough study of this neutron star and its companion using gamma-ray data and optical observations reveals a truly extreme binary system. Material evaporated from the companion star likely blocks radio waves from the neutron star.

On 22 May 2018, the two GRACE Follow-On satellites launched into Earth orbit on a Falcon-9 rocket. The aim: to continue the GRACE satellite measurements, which is important among other things for climate research, by monitoring the Earth's gravitational field. On board: A laser interferometer from the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hanover, which will serve as a model for future missions and as a step towards the LISA gravitational wave observatory. The first very promising preliminary results are already coming in before the science phase.

On 14 September 2015, the Advanced LIGO instruments detected gravitational waves for the first time ever. The signal came from the merger of two black holes, each with the mass of about 30 Suns, in a distance of 1.3 billion light-years to Earth. Albert Einstein had predicted the existence of these ripples in spacetime in 1916. The first hours of this discovery of the century took place at the Max Planck Institute for Gravitational Physics in Hannover in Bruce Allen's “Observational Relativity and Cosmology” division. The authors were also the first persons to see the signal.

The LISA Pathfinder satellite mission demonstrates core technologies for future gravitational-wave observatories in space like eLISA. These observatories will study low-frequency gravitational waves, which are emitted by, e. g., binary supermassive black holes or galactic binary stars. LISA Pathfinder was launched on December 3, 2015, and has commenced its science operations in March 2016. LISA Pathfinder will lead to a comprehensive model of all significant physical noise sources that can be extrapolated to the eLISA mission.

Gravitational waves are predicted by the general theory of relativity. Binary systems consisting of neutron stars and black holes generate these tiny ripples in space-time, which are expected to be directly measured by large-scale interferometric detectors. Not only the measurement method, but also the data analysis is paramount for the first discoveries, since only sensitive and efficient methods can filter the weak signals from the detector noise. Scientists at the MPI for Gravitational Physics (Albert Einstein Institute) have helped to bring the first discoveries closer to reality.