Tilt, Warp, and Simultaneous Precessions in Disks

TL;DR

This study uses hydrodynamic simulations to demonstrate how accretion disks around white dwarfs can naturally develop tilts, warps, and precessions, aligning with observations of V344 Lyrae.

Contribution

First simulation showing disks around white dwarfs naturally tilt, warp, and precess, explaining observed phenomena without radiation pressure.

Findings

Disks tilt and warp due to hydrodynamic lift forces.

Outer disk regions become eccentric due to tidal torques.

Precession rates match observed ratios in V344 Lyrae.

Abstract

Warps are suspected in disks around massive compact objects. However, the proposed warping source -- non-axisymmetric radiation pressure -- does not apply to white dwarfs. In this letter we report the first Smoothed Particle Hydrodynamic simulations of accretion disks in SU UMa-type systems that naturally tilt, warp, and simultaneously precess in the prograde and retrograde directions using white dwarf V344 Lyrae in the Kepler field as our model. After ~79 days in V344 Lyrae, the disk angular momentum L_d becomes misaligned to the orbital angular momentum L_o. As the gas stream remains normal to L_o, hydrodynamics (e.g., the lift force) is a likely source to disk tilt. In addition to tilt, the outer disk annuli cyclically change shape from circular to highly eccentric due to tidal torques by the secondary star. The effect of simultaneous prograde and retrograde precession is a warp of the colder, denser midplane as seen along the disk rim. The simulated rate of apsidal advance to nodal regression per orbit nearly matches the observed ratio in V344 Lyrae.