The formation and evolution of the first Supermassive Black Holes (SMBHs) observed in quasars at z > 6, is currently one of the hottest debated issues in astrophysics.
Actually, it is unclear how to form such massive objects in less than 1 Gyr from the Big Bang.
Stellar Black holes seeds, originating from the collapse of first stars, could be the possible progenitors only if super-Eddington accretion can be sustained for a sufficient amount of time.
Alternatively to this channel, many theorists have also considered the existence of a heavier mass black hole seeds, the Direct Collapse Black Holes, forming from the direct collapse of pristine clouds in particular primordial environments, appearing at a later time respect to first stars.
Both scenario occur in the very far Universe, during the epoch of reionization.
The main problem is that actually, there is a lack of comprehension around this epoch, when these seeds are expected to form and grow.
Actually no observations exist that could reveal us any physical process standing over the possible origin of SMBHs, and numerical simulations are the only possibility to investigate this missing link.
The purpose of this project is to focus on interesting environments where condition for super Eddington accretion can be met in the old Universe, considering concurrently all the possible scenario on the SMBH formation, from heavy to light mass seeds, focusing both on cosmological and local simulations.
Until now there is not any semi-analytical model which takes into account the results from the last generation 3D accretion disk simulations.
The results will be then used as sub-grid prescriptions for cosmological simulation, that actually are not sensitive to this scale.
So, working with the well tested N-body code GASOLINE, the results of these simulations will be used as sub-grid prescriptions in a simulation of a small cosmological volume that allows to resolve the small galaxies at z > 10 where BH seeds are expected to form and to grow. The predictions of these simulations will be relevant for gravitational wave detection in the LISA discovery space.
Moreover, an interesting by-product of our cosmological model is the prediction of the rate of coalescences of BH binaries that follow the cosmological halo-halo mergers along the hierarchical build-up of the quasar host dark matter halo. We know the masses and redshift of coalescence and we can estimate the gravitational wave (GW)
signal that is produced. In particular, in this project we will show how third generation GW telescopes from
the ground and in space, such as the Einstein Telescope and the LISA mission, will be able to detected the
signals produced by BH seeds binaries at very high redshift. We predict that ET will be sensitivity to BH
mergers coming from light BH seeds, while LISA will be sensitive to BH mergers coming from systems
where at least one of the two BHs originate from a heavy seed (or an intermediate-mass BH). This opens
up the possibility to investigate SMBH formation, the nature of the first BH seeds, their subsequent
accretion history, and, more generally, about the early hierarchical structure formation at high redshift, using
GW telescopes.
Our work will contribute to the creation of a catalogue of coalescing black holes at high
redshift, which will be used to support the science goals of both third generation detectors.