Black holes

Accretion onto black holes is one of the most powerful sources of energy for astrophysical objects. We study several dynamical processes related to black hole accretion and its electromagnetic emission. Specific themes of interest are:

Tidal Disruption events

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. These events appear also as bright, transient emission over a wide range of electromagnetic frequencies, typically in the UV and soft X-rays, but occasionally also in the gamma and radio regime. The combination of electromagnetic and gravitational emission allows us to study the elusive intermediate massive black holes.

Black hole binaries

We study how the interplay between binary black holes and the gaseous discs that surround them can lead or not to their merger, and what would be the electromagnetic emission associated with such processes. We study both supermassive black hole binaries (which may be relevant for the LISA interferometer) and stellar mass black hole binaries (relevant for LIGO/Virgo).

Black hole spin evolution and disc warping

Relativistic frame dragging (resulting in Lense-Thirring precession) can warp the accretion disc around a spinning black hole. We study both analytically and through hydrodynamical simulations the warping and tearing of such a disc, relating the resulting configuration to possible observed features in the spectrum of accretion black hole systems, such as Quasi Periodic Oscillations (QPO) in X-ray binaries.

Neutron Stars

[People working on this topic: Pierre Pizzochero]

Neutron stars are possibly the most exotic objects in the Universe: the intense gravitational field yields internal conditions of density and temperature far beyond those reacheable in terrestrial laboratories, so that observations of neutron stars can be used as probes of the properties of hadronic matter under extreme conditions.

In particular, the neutrons inside the star are expected to to condense in a  superfluid state and form quantized vortices, weakly interacting with the normal matter. This is manifested in pulsar glitches, sudden spin-ups of the otherwise spinning-down neutron star.

The interest of the group is the study of such glitches, both at the microscopic level and through macroscopic modelling of the phenomenon. When fitted to the available observations, these models can constrain several internal properties of the neutron star.