The Dynamical Effects of White Dwarf Birth Kicks in Globular Star Clusters

TL;DR

This paper investigates how white dwarf birth kicks influence globular cluster evolution, showing that such kicks can significantly alter cluster core dynamics and match observed white dwarf distributions.

Contribution

It introduces a Monte Carlo simulation incorporating white dwarf kicks, revealing their impact on cluster structure and white dwarf spatial distribution, which was not previously modeled.

Findings

White dwarf kicks significantly delay core contraction.

Kicks increase the core to half-mass radius ratio by up to tenfold.

Model reproduces observed radial distribution trends of white dwarfs.

Abstract

Recent observations of the white dwarf (WD) populations in the Galactic globular cluster NGC 6397 suggest that WDs receive a kick of a few km/s shortly before they are born. Using our Monte Carlo cluster evolution code, which includes accurate treatments of all relevant physical processes operating in globular clusters, we study the effects of the kicks on their host cluster and on the WD population itself. We find that in clusters whose velocity dispersion is comparable to the kick speed, WD kicks are a significant energy source for the cluster, prolonging the initial cluster core contraction phase significantly so that at late times the cluster core to half-mass radius ratio is a factor of up to ~ 10 larger than in the no-kick case. WD kicks thus represent a possible resolution of the large discrepancy between observed and theoretically predicted values of this key structural parameter. Our modeling also reproduces the observed trend for younger WDs to be more extended in their radial distribution in the cluster than older WDs.