deeplink to this page         student projects         teaching

Utrecht University

Student project: the formation of compact-binary sources for LIGO and Virgo

Background

Gravitational waves (GWs) were first detected directly by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015. This was a compact-binary coalescence (CBC). The high masses of the two black holes (BHs; 30-35Mo) was a complete surprise to many theoreticians - most models predicted BH masses in the range 5-15Mo. Even current stellar-evolution and population-synthesis codes predict such low masses for the default assumptions.

The evolution of massive stars that produce black holes and neutron stars (NSs) is notoriously poorly constrained, due to the fact that these objects are relatively rare. It is clear that the metallicity of the star and the assumptions for the stellar wind of massive stars play a key role in the type of remnant (NS or BH) and their masses. This project aims to map the different assumptions for such parameters to the resulting population of NS-NS, BH-NS and BH-BH binaries observable by GW detectors like LIGO, Virgo and KAGRA (LVK). We use the BSE binary-population-synthesis code BSE (Hurley et al 2002) and compare them to the observed GW sources. Of particular interest are the ratios between the three different types of binaries, the masses of the BHs and the mass ratios of the BH-BH binaries.

Research questions

  • How does the population of CBCs observable by the LVK depend on the assumptions of stellar and binary evolution?
  • What are the properties of the ZAMS binaries that evolve into the observed CBCs?

Methods

This project involves using our version of the population-synthesis code BSE, creating model populations of observable GW sources for different combinations of assumptions, and comparing the resulting model populations to those observed by LVK so far. Assumptions to play with are those of metallicity, stellar wind, conservation of mass transfer, specific angular momentum of any lost material, details of the supernova and common-envelope parameters. This should result in an overview of which parameters play an important role, how these dependencies run and how difficult it is to explain the observed GW sources. In addition, we can learn the specifics of the initial population of ZAMS binaries that evolve into these observable GW events.

Interested?

If you are interested in this project, please send me an email. If I'm on holiday (e.g. the beginning of January or September), send me a WhatsApp on my mobile to expedite things. (There will be plenty of arranging and reading for you to do until I get back, see Getting started.) You can find my email address and phone number on my home page.


Back to student projects.