Giuseppe Lodato – Research

Young stars are generally surrounded by dust and gas discs from which they accrete material and grow in mass. These discs are supposed to be the site where planet formation occurs. I am interested in the hydrodynamics of such discs, with emphasis on the role of gravitational instabilities in redistributing angular momentum and favouring accretion. I have also studied the effect of such instabilities in the formation of planetesimals (the building blocks of planets) and possibly of the planets themselves.

Relevant publications

• Gravitational instabilities in protostellar disks, Kratter & Lodato, ARA&A, 54, 271 (2016)
• Testing the locality of transport in self-gravitating accretion discs, Lodato & Rice, MNRAS, 351, 630 (2004)
• Chaotic star formation and the alignment of stellar rotation with disc and planetary orbital axes, Bate, Lodato & Pringle, MNRAS, 401, 1505 (2010)

Accretion discs are subject to several dynamical processes. In particular, I am interested in the development of gravitational instabilities, and in assessing their role in the process of angular momentum transport within the disc. 

I am also interested in the evolution of warped accretion discs. A spinning black hole exerts a relativistic torque on matter whose orbital plane is inclined with respect to the equatorial plane of the black hole. This causes the orbits of rotating matter to precess around the black hole spin axis. An accretion disc around such a spinning black hole will therefore attain a warped shape. I am studying the consequences of this warping process on the secular evolution of the black hole – accretion disc system and on observables from Active Galactic Nuclei.

I also run large numerical simulations to determine accurately the speed at which such warps propagate in a thin and viscous disc.

Relevant publications

• Wave-like warp propagation in circumbinary discs – I. Analytic theory and numerical simulations, Facchini, Lodato & Price, MNRAS, 433, 2142 (2013)
• On the diffusive propagation of warps in thin accretion discs, Lodato & Price, MNRAS, 405, 1212 (2009)
• Warp diffusion in accretion discs: a numerical investigation, Lodato & Pringle, MNRAS, 381, 1287 (2006)

In order to power the AGN which are observed at very large red-shifts, supermassive black holes have to form very early on, when the Universe was very young. I have developed a model for the formation of the seeds of such SMBH at large redshift. This model relates their properties (like their mass) to the properties of the dark matter halo inside which they are formed. These model can be used to determine the abundance of such seeds and their mass distribution. I also study other growth processes for black holes, such as mergers with other black holes (which might provide an important mechanism for the production of gravitational waves, that can be observed by upcoming missions such as LISA).

Relevant publications

• Supermassive black hole formation during the assembly of pre-galactic discs, Lodato & Natarajan, MNRAS, 371, 1813 (2006)
• The evolution of massive black hole seeds, Volonteri, Lodatto & Natarajan, MNRAS, 383, 1079 (2008)
• Black hole mergers: can gas discs solve the `final parsec’ problem?, Lodato, Nayakshin, King & Pringle, MNRAS, 398, 1392 (2009) 

Tidal disruption events occur when a star approaches a black hole within a distance such that the immense tidal forces of the hole overcome the internal gravity of the star and rip it apart. Several dozen candidates of such eventts have been reported, and they appear as bright, transient emission with enormous luminosity (possibly above the Eddington limit), over a wide range of electromagnetic frequencies, typically in the UV and soft X-rays, but occasionally also in the gamma and radio regime. Such events are extremely important as probe of supermassive black hole properties in quiescent galaxies and may even be source of gravitational wave emission.

Relevant publications

• Stellar disruption by a supermassive black hole: is the light curve really proportional to t^(-5/3)?, Lodato, King & Pringle, MNRAS, 392, 332 (2009)
• Multiband light curves of tidal disruption events, Lodato & Rossi, MNRAS, 410, 359 (2011)
• Disc formation from tidal disruptions of stars on eccentric orbits by Schwarzschild black holes, Bonnerot, Rossi, Lodato & Price, MNRAS, 455, 2253 (2016)