No Black Holes in NGC 6397

Abstract

Recently, \citet{vitral2021does} detected a central concentration of dark objects in the core-collapsed globular cluster NGC 6397, which could be interpreted as a subcluster of stellar-mass black holes. However, it is well established theoretically that any significant number of black holes in the cluster would provide strong dynamical heating and is fundamentally inconsistent with this cluster's core-collapsed profile. Claims of intermediate-mass black holes in core-collapsed clusters should similarly be treated with suspicion, for reasons that have been understood theoretically for many decades. Instead, the central dark population in NGC 6397 is exactly accounted for by a compact subsystem of white dwarfs, as we demonstrate here by inspection of a previously published model that provides a good fit to this cluster. These central subclusters of heavy white dwarfs are in fact a generic feature of core-collapsed clusters, while central black hole subclusters are present in all {\em non\/}-collapsed clusters.

3 pages, 1 figure, to submit to AAS journals

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Cited by in corpus (5)

• Stellar Escape from Globular Clusters. I. Escape Mechanisms and Properties at Ejection
• Growing Black Holes through Successive Mergers in Galactic Nuclei: I. Methods and First Results
• Stellar graveyards: Clustering of compact objects in globular clusters NGC 3201 and NGC 6397
• Formation of Low-mass Black Holes and Single Millisecond Pulsars in Globular Clusters
• Gravitational Microlensing Rates in Milky Way Globular Clusters