Secular Evolution Driven by Massive Eccentric Disks/Rings: An Apsidally Aligned Case

TL;DR

This paper develops an analytical framework to study the secular evolution of test particles influenced by massive, eccentric, apsidally aligned disks, applicable to various astrophysical systems, and verifies it through numerical orbit integrations.

Contribution

It introduces a new analytical method relating disk surface density and eccentricity profiles to secular dynamics without ad hoc softening, verified for low eccentricities.

Findings

Precession can change from prograde to retrograde within the disk.

Sharp features like edges and gaps enhance precession effects.

Locations where precession changes sign see significant eccentricity growth.

Abstract

Massive eccentric disks (gaseous or particulate) orbiting a dominant central mass appear in many astrophysical systems, including planetary rings, protoplanetary and accretion disks in binaries, and nuclear stellar disks around supermassive black holes in galactic centers. We present an analytical framework for treating the nearly Keplerian secular dynamics of test particles driven by the gravity of an eccentric, apsidally aligned, zero-thickness disk with arbitrary surface density and eccentricity profiles. We derive a disturbing function describing the secular evolution of coplanar objects, which is explicitly related (via one-dimensional, convergent integrals) to the disk surface density and eccentricity profiles without using any ad hoc softening of the potential. Our analytical framework is verified via direct orbit integrations, which show it to be accurate in the low-eccentricity limit for a variety of disk models (for disk eccentricity < 0.1-0.2). We find that free precession in the potential of a disk with a smooth surface density distribution can naturally change from prograde to retrograde within the disk. Sharp disk features - edges and gaps - are the locations where this tendency is naturally enhanced, while the precession becomes very fast. Radii where free precession changes sign are the locations where substantial (formally singular) growth of the forced eccentricity of the orbiting objects occurs. Based on our results, we formulate a self-consistent analytical framework for computing an eccentricity profile for an aligned, eccentric disk (with a prescribed surface density profile) capable of precessing as a solid body under its own self-gravity.