A comment on "Why is the Galactic disk so cool?", by Hamilton et al

TL;DR

This paper discusses the discrepancy between observed and modeled rates of stellar diffusion and heating in the Milky Way disk, emphasizing that earlier models can explain the observations without additional mechanisms.

Contribution

It demonstrates that previous radial migration models from 2002, once corrected, align with recent findings, challenging the need for alternative heating mechanisms.

Findings

Earlier models explain observed diffusion rates

Corrected models account for slow heating in the disk

Additional heating mechanisms are unlikely to be significant

Abstract

Frankel et al (2020) reported that the rate of diffusion in angular momentum by stars in the disk of the Milky Way was about ten times faster than the rate of heating, which places a stringent requirement on the nature of disk star scattering. In a recent posting, Hamilton et al (2024) integrated orbits of test particles in a Galactic model that included transient spirals, and found that the ratio of the rates heating to radial migration in their calculations was generally larger than reported by Frankel et al. They concluded that the observed slow heating rate poses a significant challenge to dynamical models of the Milky Way and seemed to require revision of our current theories of spiral structure. Here we show that that our earlier models of radial migration we published in 2002, after correction for 3D motion, account naturally for the finding of Frankel et al, but leave little room for additional heating by mechanisms other than transient spirals.