Eccentric Tidal Disruption Event Disks around Supermassive Black Holes: Dynamics and Thermal Emission

TL;DR

This paper models highly eccentric tidal disruption event disks around supermassive black holes, showing they can produce thermal emission consistent with observed X-ray and optical luminosities, and highlights stream collisions as a key emission mechanism.

Contribution

It introduces a novel eccentric disk model incorporating relativistic precession and adiabatic communication, explaining observed TDE emissions better than traditional circular disk models.

Findings

Eccentric TDE disks can match observed X-ray and UV/Optical luminosities.

Stream-stream collisions are a promising power source for optically bright TDEs.

Highly eccentric solutions exist for realistic SMBH and stellar parameters.

Abstract

After the Tidal Disruption Event (TDE) of a star around a SuperMassive Black Hole (SMBH), if the stellar debris stream rapidly circularizes and forms a compact disk, the TDE emission is expected to peak in the soft X-ray or far Ultra-Violet (UV). The fact that many TDE candidates are observed to peak in the near UV and optical has challenged conventional TDE emission models. By idealizing a disk as a nested sequence of elliptical orbits which communicate adiabatically via pressure forces, and are heated by energy dissipated during the circularization of the nearly parabolic debris streams, we investigate the dynamics and thermal emission of highly eccentric TDE disks, including the effect of General-Relativistic apsidal precession from the SMBH. We calculate the properties of uniformly precessing, apsidally aligned, and highly eccentric TDE disks, and find highly eccentric disk solutions exist for realistic TDE properties (SMBH and stellar mass, periapsis distance, etc.). Taking into account compressional heating (cooling) near periapsis (apoapsis), we find our idealized eccentric disk model can produce emission consistent with the X-ray and UV/Optical luminosities of many optically bright TDE candidates. Our work attempts to quantify the thermal emission expected from the shock-heating model for TDE emission, and finds stream-stream collisions are a promising way to power optically bright TDEs.