On the Radial Distribution of White Dwarfs in the Globular Cluster NGC 6397

TL;DR

This study investigates the radial distribution of white dwarfs in NGC 6397, revealing that young white dwarfs are more extended than expected, challenging existing models of stellar dynamics in globular clusters.

Contribution

It provides the first detailed analysis of the radial distribution of young white dwarfs in NGC 6397, highlighting unexpected extended distributions.

Findings

Young white dwarfs are more radially extended than their progenitors.

The distribution of young white dwarfs differs from that of old white dwarfs.

Results challenge current models of stellar relaxation in globular clusters.

Abstract

We have examined the radial distribution of white dwarfs over a single HST/ACS field in the nearby globular cluster NGC 6397. In relaxed populations, such as in a globular cluster, stellar velocity dispersion, and hence radial distribution, is directly dependent on stellar masses. The progenitors of very young cluster white dwarfs had a mass of ~0.8 solar masses, while the white dwarfs themselves have a mass of ~0.5 solar masses. We thus expect young white dwarfs to have a concentrated radial distribution (like that of their progenitors) that becomes more extended over several relaxation times to mimic that of ~0.5 solar mass main-sequence stars. However, we observe young white dwarfs to have a significantly extended radial distribution compared to both the most massive main sequence stars in the cluster and also to old white dwarfs.