Magnetorotational instability in eccentric disks

Understand

Eccentric disks arise in such astrophysical contexts as tidal disruption events, but it is unknown whether the magnetorotational instability (MRI), which powers accretion in circular disks, operates in eccentric disks as well.

• We examine the linear evolution of unstratified, incompressible MRI in an eccentric disk orbiting a point mass.
• We consider vertical modes of wavenumber $k$ on a background flow with uniform eccentricity $e$ and vertical Alfv\'en speed $v_\mathrm A$ along an orbit with mean motion $n$.
• We find two mode families, one with dominant magnetic components, the other with dominant velocity components; the former is unstable at $(1-e)^3f^2\lesssim3$, where $f\equiv kv_\mathrm A/n$, the latter at $e\gtrsim0.8$.