Title:
Formation of an accretion flow in tidal disruption events

Abstract:
After the star has been tidally disrupted by the black hole, 
the debris forms an elongated stream, half of which falls back 
near the compact object. Owing to different sources of dissipation, 
this returning matter evolves at later times into a more circular structure 
to eventually form an accretion flow. Although no clear consensus 
has yet been reached about this stage of evolution, I will review 
the different ongoing efforts in this direction. An important dissipation 
mechanism consists in a self-crossing shock experienced by the stream 
due to relativistic apsidal precession, although this collision may be delayed 
for a rotating black hole. Local simulations find that the outcome of 
this interaction is a quasi-spherical expansion of the shocked gas due to 
radiation pressure that can unbind a fraction of the mass. Investigating 
the subsequent global hydrodynamical evolution is numerically challenging 
and has therefore only been studied under simplifying assumptions. 
These works find that additional dissipation takes place that ultimately 
results in the formation of a thick and extended torus. The debris may take 
a long time to settle into this final configuration, with the possibility of retaining 
significant eccentricities. Importantly, this picture of disc formation drastically 
differs from that assumed in pioneering investigations. During this process, 
the circularizing shocks significantly heat the stellar matter that likely produces 
the first light observable from these events. The resulting gas distribution sets 
the initial configuration, from which the matter subsequently gets viscously 
accreted onto the black hole.