Astrophysics & Particle Physics-APPC 2026

Accretion flow instabilities are processes that happen in accretion disks around compact objects like black holes, neutron stars, and white dwarfs. Instabilities in these systems are fundamental in controlling the transport of angular momentum, disk turbulence, and luminosity variability, shaping astrophysical system evolution.A key mechanism for instabilities is the magnetorotational instability (MRI) that occurs in differentially rotating, magnetized disks. MRI generates turbulence, enhancing angular momentum transport, allowing material to spiral inward and accrete onto the central object. Other instabilities, including thermal, viscous, and gravitational instabilities, can produce fluctuations in disk density, temperature, and magnetic field structures.Accretion flow instabilities are closely linked to high-energy astrophysical phenomena.

For instance, in active galactic nuclei (AGN) and X-ray binaries, accretion flow instabilities may produce optical and X-ray variability on short timescales, impact the acceleration of relativistic jets, and lead to episodic outbursts. Disk oscillations due to these instabilities also give rise to quasi-periodic oscillations (QPOs) in X-ray light curves, which serve diagnostic purposes for examining disk structure and compact object properties.Numerical simulations and magnetohydrodynamic (MHD) models are crucial for explaining accretion flow instabilities. These models facilitate the exploration of nonlinear instability evolution, generation of turbulence, and interaction with magnetic fields. Observations throughout the electromagnetic spectrum—from radio to X-rays—supplement simulations by uncovering the signatures of instabilities in accretion disks around various compact objects.Altogether, accretion flow instabilities are central to accretion disk physics and the high-energy phenomena they give rise to. Observing these instabilities provides astronomers with knowledge on disk dynamics, angular momentum transport, jet production, and the variable nature of black holes, neutron stars, and other compact astrophysical objects. These processes are essential for the modeling of cosmic accretion and energy release in the universe.