Radiation pressure instability: from heart-beat states in black hole binary systems to Quasars and Changing-Look AGN

TL;DR

This paper reviews the radiation-pressure instability in accretion disks, linking phenomena from black hole binary heartbeat states to quasar variability and Changing-Look AGN, highlighting its broad astrophysical implications.

Contribution

It synthesizes observational and theoretical insights on radiation-pressure instability across different astrophysical systems, emphasizing its role in diverse variability phenomena.

Findings

Empirical support for instability in stellar-mass black holes

Connection between disk instability and AGN duty cycles

Role of instability in Changing-Look AGN transitions

Abstract

Radiation-pressure instability was identified soon after the seminal classical accretion disk models of Shakura-Sunyaev and Novikov-Thorne, yet its full implications remain an active area of investigation. These models form the backbone of our understanding of accretion onto compact objects and successfully describe the phenomenology of black hole and neutron star X-ray binaries, as well as luminous active galactic nuclei (AGN), in the regime of high mass accretion rates. At luminosities approaching a significant fraction of the Eddington limit (L/LEdd > 0.1), standard thin disks are predicted to become thermally unstable due to the dominance of radiation pressure. This prediction has found empirical support in several Galactic stellar-mass black hole systems, where the instability manifests as quasi-periodic, large-amplitude luminosity oscillations, so-called "heartbeat states", and has been proposed as a driver of observed signatures of deterministic chaos in accretion-driven light curves. The scope of radiation-pressure-induced variability extends beyond stellar-mass black holes: both black holes across mass scales and accreting neutron stars can exhibit related behavior, though the presence of a boundary layer in neutron stars adds complexity and offers a unique laboratory for testing the interplay between accretion dynamics and the central object. On extragalactic scales, the instability has been invoked to explain the duty cycles and apparent short lifetimes of radio-loud AGN, as well as the dramatic spectral-state transitions seen in Changing-Look AGN. (...)