Directory
Massive black hole formation
Although we can infer the existence of SMBHs in nearby and faraway galaxies, their formation route remains a mystery. A black hole weighing a billion solar masses cannot be formed simply as the endpoint of a star as massive as a few billion suns, since the gas that would form such a star would fragment into smaller stars before it could become a single proto-star.
Smaller black holes, as massive as hundreds, thousands, or even millions of solar masses, could have formed along several possible evolutionary paths in the centers of very distant galaxies, galaxies that existed when the Universe was very young. It is possible that such 'seed' black holes have evolved through time to become the SMBHs that we see now. A famous diagram created in 1978 by Martin Rees shows several possible formation scenarios for SMBHs (left).
They divide naturally into two broad groups: one might call them 'plus-size' and 'petite.' The 'plus-size' scenarios predict that black holes begin their lives already quite large -- a few tens of thousands of solar masses up to a few million solar masses, formed from the direct monolithic collapse of gas in galactic centers. The 'petite' scenarios predict that black holes begin small - perhaps only hundred of solar masses, formed as endpoints in the evolution of the first generation of stars in the Universe. These first stars are thought to have been much more massive then the current generation, and their remnants could well have been the seeds of the SMBHs we see today.
Cosmic Structures
These seeds must have formed in the very young Universe. Proof for this is the observation of very distant quasars, that we identify as luminous and powerful sources when the age of the Universe was not even one billion years. For the light from these quasars to be bright enough notwithstanding the humongous distance between us and the young quasar, the black holes powering them must be as massive as a few billion suns.
The evolution of these seeds from the dawn of the Universe until now is a complicated combination of various processes, that make the black holes big, fast, powerful.The history of black holes is interlaced with the history of the galaxies that host them. Black holes must be studied and understood within the 'cosmic web' (left) that describes how structures, like our own galaxy, matured in the ever-evolving Cosmos.
Selected Publications
- Early reionization by miniquasars
- Formation of supermassive black holes by direct collapse in pre-galactic haloes
- Quasars at z=6: the survival of the fittest
- Formation of the First Nuclear Clusters and Massive Black Holes at High Redshift
- The importance of dry and wet merging on the formation and evolution of elliptical galaxies
Research Interests
- Cosmology and structure formation
- Black hole evolution and dynamics
- Gravitational waves
- Accretion processes and active galactic nuclei