Directory
Massive black holes evolution
However large or small their initial seeds, once black holes formed, somehow they evolved to become the SMBHs we see today.
The seeds start growing in mass as they accrete the in-falling surrounding matter, and while this is happening, we could expect to be able to observe them as quasars (left). In fact, we do observe the strongest of such quasars, at distances corresponding to a time when the Universe was only one-tenth of its current age, and we infer that they are powered by billion-solar-mass black holes.
Astrophysical black holes are characterized by two parameters, or 'two hairs', only: mass and spin. Theory predicts that a large fraction of SMBHs should be spinning rapidly, due to interaction between the black hole spins and the angular momentum of the accretion disc. This prediction is still to be proved. Measuring SMBH spins is an arduous task, and all current evidence is indirect.
No doubt there are 'mini-quasars' powered by smaller black holes (with masses of a few thousand solar masses, say), which formed at even earlier times. Future planned X-ray missions such as XEUS and Constellation-X, or near-infrared facilities such as JWST, will be able to detect accreting black holes as small as about a few million solar masses in the very early Universe. The Chandra Deep Field North image (right) is the most sensitive X-ray exposure ever made. Most of the sources are quasar powered by supermassive black holes located in the centers of galaxies
Not all black holes in the Universe are quasar though. 'Black' black holes might be invisible to the eye of telescopes, but they are not silent to the ears of gravitational waves detectors.
Selected Publications
- The assembly and merging history of supermassive black holes in hierarchical models of galaxy formation
- Cosmological Black Hole Spin Evolution by Mergers and Accretion
- The distribution and cosmic evolution of massive black hole spins
- Rapid growth of high-redshift black holes
- Constraints on the accretion history of massive black holes from faint X-ray counts
- Black hole spin and galactic morphology
- The evolution of massive black hole seeds
Research Interests
- Cosmology and structure formation
- Black hole evolution and dynamics
- Gravitational waves
- Accretion processes and active galactic nuclei