Directory
Gravitational waves from massive black holes
To undestand how black holes are born and grow up we need to collect as much information as possible, using techniques at the edge of what technology ca do.
An alternative way to learn about the massive black hole population is to look for signatures of their mergers through emission of gravitational radiation (right).
The mergers of black holes that exist in binary systems are predicted to be the strongest signals that the planned gravitational waves telescope LISA can detect. Black hole mergers will be visible to LISA even for black holes as small as just a thousand solar masses, almost independent of their redshift.
In the currently favored cosmological model, galaxies form in a hierarchical fashion, starting from small systems at early times, and then growing via mergers. The formation history of galaxies is often described as a merger tree: the 'trunk', a galaxy that we observe today, can be traced back through its merger history to the high-redshift smaller branches (left). If black holes formed at early times, they are bound to follow the merger hierarchy experienced by their host galaxies. Black hole mergers are therefore expected to be common in the Universe.
When two galaxies both hosting central black holes merge (right), simple physical arguments suggest that the black holes can indeed sink to the center of the merged galaxy, form a binary system with separation of around a parsec and eventually coalesce by emission of gravitational radiation.
The questions asked by astrophysicists studying supermassive black-hole mergers deal both with the number of SMBHs in the Universe, and the dynamics and efficiency of the merger process. How often a galaxy hosts a black hole influences the number of binaries that can form. The dynamics and efficiency of black-hole mergers in galactic centers determine how many of the binaries can actually get into the interesting regime for gravitational-wave detection.
Selected Publications
- Low frequency gravitational radiation from coalescing massive black hole binaries in hierarchical cosmologies
- The gravitational wave signal from massive black hole binaries and its contribution to the LISA data stream
- Massive black-hole binary inspirals: results from the LISA parameter estimation taskforce
Research Interests
- Cosmology and structure formation
- Black hole evolution and dynamics
- Gravitational waves
- Accretion processes and active galactic nuclei