Dynamical structure of highly eccentric discs with applications to tidal disruption events

TL;DR

This paper investigates the dynamical vertical structure of highly eccentric tidal disruption event discs using nonlinear theory, revealing complex behaviors like nozzle structures and potential thermal instabilities.

Contribution

It introduces a detailed nonlinear model of eccentric TDE discs that accounts for vertical structure, viscous dissipation, and cooling, extending beyond previous numerical simulations.

Findings

Identification of nozzle-like structures in eccentric discs.

Evidence for thermal instability in radiation-pressure dominated discs.

Many models suggest the $mbda$-prescription may fail in these conditions.

Abstract

Whether tidal disruption events circularise or accrete directly as highly eccentric discs is the subject of current research and appears to depend sensitively on the disc thermodynamics. One aspect of this problem that has not received much attention is that a highly eccentric disc must have a strong, non-hydrostatic variation of the disc scale height around each orbit. As a complement to numerical simulations carried out by other groups, we investigate the dynamical structure of TDE discs using the nonlinear theory of eccentric accretion discs. In particular, we study the variation of physical quantities around each elliptical orbit, taking into account the dynamical vertical structure, as well as viscous dissipation and radiative cooling. The solutions include a structure similar to the nozzle-like structure seen in simulations. We find evidence for the existence of the thermal instability in highly eccentric discs dominated by radiation pressure. For thermally stable solutions many of our models indicate a failure of the $\alpha-$prescription for turbulent stresses. We discuss the consequences of our results for the structure of eccentric TDE discs.