Stability and Damping in the Disks of Massive Galaxies

TL;DR

This paper proposes a mechanism involving gravitational interactions with interstellar matter and exo-Oort objects that explains rapid damping of large velocity disturbances in galaxy disks, maintaining their long-term stability.

Contribution

It introduces a new damping mechanism based on gravitational interactions with interstellar and exo-Oort objects, explaining galaxy disk stability over billions of years.

Findings

Rapid damping of large perturbations within short timescales

Explains observed velocity dispersions in the Milky Way

Supports long-term stability of galaxy disks

Abstract

After their initial formation, disk galaxies are observed to be rotationally stable over periods of >6 Gyr, implying that any large velocity disturbances of stars and gas clouds are damped rapidly on the timescale of their rotation. However, it is also known that despite this damping, there must be a degree of random local motion to stabilize the orbits against degenerate collapse. A mechanism for such damping is proposed by a combination of inter-stellar gravitational interactions, and interactions with the Oort clouds and exo-Oort objects associated with each star. Analysis of the gravitational interactions between two stars is a three-body problem, because the stars are also in orbit round the large virtual mass of the galaxy. These mechanisms may produce rapid damping of large perturbations within a time period that is short on the scale of observational look-back time, but long on the scale of the disk rotational period for stars with small perturbations. This mechanism may also account for the locally observed mean perturbations in the Milky Way of 8-15~km/s for younger stars and 20-30~km/s for older stars.