A new globular cluster black hole in NGC 4472

TL;DR

This paper reports the discovery of a new black hole candidate in a globular cluster within NGC 4472, based on X-ray variability and spectral analysis, suggesting black hole formation is linked to cluster properties.

Contribution

It presents the identification of a new globular cluster black hole candidate and analyzes its properties in relation to cluster characteristics, a novel addition to extragalactic black hole studies.

Findings

The source varies by at least a factor of 4 in luminosity.

The peak luminosity exceeds 2×10^{39} ergs/sec, surpassing neutron star limits.

Black hole candidates are more common in bright, metal-rich clusters.

Abstract

We discuss CXOU~1229410+075744, a new black hole candidate in a globular cluster in the elliptical galaxy NGC~4472. By comparing two Chandra observations of the galaxy, we find a source that varies by at least a factor of 4, and has a peak luminosity of at least $2\times10^{39}$ ergs/sec. As such, the source varies by significantly more than the Eddington luminosity for a single neutron star, and is a strong candidate for being a globular cluster black hole. The source's X-ray spectrum also evolves in a manner consistent with what would be expected from a single accreting stellar mass black hole. We consider the properties of the host cluster of this source and the six other strong black hole X-ray binary candidates, and find that there is suggestive evidence that black hole X-ray binary formation is favored in bright and metal rich clusters, just as is the case for bright X-ray sources in general.