Dynamics and radiation from tidal disruption events

Abstract

When a star gets too close to a supermassive black hole,

it is torn apart by strong tidal forces in a tidal disruption event (TDE).

The stellar matter then fuels the compact object causing a bright flare that

is a unique probe of the majority of galactic nuclei, otherwise quiescent. For example, the black hole properties can be estimated from this signal. In my thesis, I used analytical and numerical methods to shed light on the TDE dynamics and associated emission, a required step to optimally exploit this powerful predictive potential. I carried out a numerical study of the accretion disc formation from the stellar debris. The results strongly challenged previous assumptions, showing that this process can be slower and result in a more extended gas distribution than previously thought. In addition, I analytically demonstrated that disc formation can be accelerated if the stellar matter is significantly magnetized. I then highlighted the impact of hydrodynamical instabilities on the debris that can cause an efficient mixing with the surrounding gas, likely dimming the associated flare. Finally, I numerically studied the disruption of magnetized stars, proving that it can produce a thick debris distribution or result in a magnetically amplified remnant.