# Evolution of relativistic thin discs with a finite ISCO stress: II. Late time behaviour

## TL;DR

This paper develops a relativistic thin disc model with finite ISCO stress, revealing a three-stage evolution including a novel 'stalled accretion' phase, supported by simulations and observations.

## Contribution

It introduces a continuous model for relativistic thin discs with finite ISCO stress, incorporating sub-circular velocities and identifying a new 'stalled accretion' stage.

## Key findings

- Identification of three distinct evolutionary stages.
- Existence of a 'stalled accretion' phase.
- Model aligns with GRMHD simulations and X-ray observations.

## Abstract

We present solutions to the relativistic thin disc evolutionary equation using a modified description of the mean fluid flow within the disc. The model takes into account the effects of sub-circular velocities in the innermost disc regions, and resolves otherwise unsustainable behaviour present in simple finite ISCO stress disc models. We show that the behaviour of a relativistic thin disc evolving with a finite ISCO stress is comprised of three distinct stages which join the ordinarily distinct finite and vanishing ISCO stress solutions into a fully continuous model parameterisation. The most important prediction of our model is the existence of an intermediate stage of "stalled accretion", controlled by a single dimensionless parameter. The hallmarks of this evolutionary phase appear to have been seen in GRMHD simulations as well as in the late time X-ray observations of tidal disruption events, but dedicated simulations and extended observations are needed for a deeper understanding.