Formation of neutron star / black hole binaries and their merger rate in the local Universe

• Applicant: Professor Dr. Thomas Tauris
• Subject Area: Astrophysics and Astronomy
• Term: from 2013 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 231548287

The expected detection of gravitational waves will open a new window to the Universe and compliment our knowledge of astrophysical sources obtained from photons and neutrinos. The advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) detector, together with its European sister VIRGO and the German detector GEO 600, will be operational in 2014 and reach full sensitivity in 2015. The most promising candidate sources for transient burst detections of high-frequency gravitational waves (10 Hz - 10 kHz) are merging neutron stars (NS) and black holes (BH). These compact objects are formed in tight binaries and undergo spiral-in due to continuous emission of gravitational waves until they finally merge in a violent transient event - possibly leading to a short gamma-ray burst. The main aim of this project is to calculate theoretically the rate of such merging NS/BH in the local Universe using our best up-to-date knowledge of stellar and binary evolution. These results will be compared to the upcoming LIGO detection rates which will enable us to better constrain the input physics behind key binary stellar interactions such as mass and angular momentum loss, common envelopes, evolution of naked helium stars, the role of rapid stellar rotation in massive binaries and, finally, the momentum kick imparted to newborn NS and BH. A second aim of this project is to better understand - and to quantify - the formation, the location, the properties and the lifetimes of Galactic recycled radio pulsars orbiting NS or BH. Whereas we know of 9 radio pulsars orbiting another NS we still have no detections of a radio pulsar orbiting a BH. With this project we hope to gain theoretical knowledge about such systems which will enhance the chance of success in future radio surveys. A recycled pulsar is formed when an old NS is spun up to a high spin frequency via accretion of mass and angular momentum from a companion star in a close binary system. Many aspects of this mass-transfer process and the accretion physics involved are not well understood but play a crucial role for recycling radio pulsars to high spin rates and low B-fields, which make them detectable for billions of years to follow. A third outcome of this study is therefore a better knowledge of the evolution of high-mass X-ray binaries which again can be confronted with observations. To model the population of compact binaries the evolution of a large sample of binary star systems is needed - from the zero age main sequence, via mass transfer and supernova explosions - in order to predict the number of both observable radio pulsars orbiting NS and BH as well as the advanced LIGO detection rate of mergers. To achieve these goals we make use of advanced population synthesis techniques with Monte Carlo simulations and explore new aspects of massive binary stellar evolution for the first time.

• DFG Programme: Research Grants