New method for simulating merging neutron stars

Potsdam, 10. January 2011

AEI unveils new methods for simulating neutron stars merging

Two neutron stars in the final stages of their merger Credit: Max Plank Institute for Gravitational Wave Research (Albert Einstein Institute)

How neutron stars merge - first accurate calculation of the last orbits of binary systems of neutron stars. AEI scientists described for the first time new numerical methods for the calculation of gravitational wave signals.

An article describing an important progress in modelling the last orbits of binary systems of neutron stars has been recently published in Physical Review Letters (Physical Review Letters (Vol.105, No.26). URL: ).

Simulations of inspiralling neutron stars and black holes provide insights into the possible structure of gravitational wave signals. They significantly increase the probability of identifying gravitational waves in the detector data. The article focuses on the last few orbits before coalescence of binary neutron star systems and their experimental observation (which is expected in the coming years) by the network of gravitational wave detectors LIGO, GEO600 and Virgo - LIGO is in the United States, GEO600 is the German-British gravitational wave detector in Ruthe near Hannover, operated by the Albert Einstein Institute and Virgo is the French-Italian detector installed in Cascina, near Pisa.

By exploiting the computational power of supercomputers and by performing the most extended and accurate calculations of this process, a team of scientists from Germany, France, the U.S. and Japan was able to improve a simplified but analytical description of the inspiral stage, when the two stars are still separate but their orbit is shrinking because of the large emission of gravitational waves. The refinement of the analytic description via accurate numerical calculations has shown that it can be used with success also to describe objects with finite dimensions, such as neutron stars, extending its validity beyond the much simpler case of binary black holes. “We found out how to introduce corrections in simplified models of binary neutron stars, so that they can reproduce the results of complex numerical simulations”, says Professor Luciano Rezzolla, head of the numerical relativity group at the Albert Einstein Institute/AEI in Potsdam. This breakthrough opens the way to a large-scale modelling of the gravitational signal emitted by the last orbits of a system of two neutron stars with a precision adequate for detection.

An insight into neutron stars
In addition, the work provides important evidence that the detection of this type of signal will allow one to measure the ratio between the mass and radius of neutron stars. This measurement is potentially very important because it will give access to new information on the equation of state of ultra-dense nuclear matter, of which neutron stars are made, and which remains essentially unknown.The article is the result of a collaboration between a team of numerical and analytical theorists of Relativistic gravity: Luca Baiotti (Osaka Universities, Japan), Thibault Damour (IHÉS, France), Bruno Giacomazzo (NASA Goddard, USA), Alessandro Nagar (IHÉS, France) and Luciano Rezzolla (Albert Einstein Institute, Germany). You can find the article ‘Analytic modelling of tidal effects in the relativistic inspiral of binary neutron stars' by L. Baiotti, T. Damour, B. Giacomazzo, A. Nagar and L. Rezzolla at:

Further information and images:
Prof. Dr. Luciano Rezzolla Tel.: 0331 – 567 7246
Dr. Elke Müller, press officer Tel.: 0331 – 567 7303
Susanne Milde Milde Marketing Science Communication Tel.: 0331 – 583 93 55