Deep Chandra Observations of the Compact Starburst Galaxy Henize 2-10: X-rays from the Massive Black Hole

TL;DR

This study uses deep Chandra X-ray observations to identify and analyze a low-luminosity massive black hole in the galaxy Henize 2-10, revealing its accretion state, variability, and distinguishing it from nearby X-ray sources.

Contribution

First high-resolution, long-duration X-ray observations confirm the presence of a low-accretion massive black hole in Henize 2-10 and differentiate it from other X-ray sources.

Findings

Detected a nuclear X-ray source coincident with the black hole

Observed the black hole radiating well below its Eddington limit

Tentative 9-hour periodicity suggests possible accretion variability

Abstract

We present follow-up X-ray observations of the candidate massive black hole (BH) in the nucleus of the low-mass, compact starburst galaxy Henize 2-10. Using new high-resolution observations from the Chandra X-ray Observatory totaling 200 ks in duration, as well as archival Chandra observations from 2001, we demonstrate the presence of a previously unidentified X-ray point source that is spatially coincident with the known nuclear radio source in Henize 2-10 (i.e., the massive BH). We show that the hard X-ray emission previously identified in the 2001 observation is dominated by a source that is distinct from the nucleus, with the properties expected for a high-mass X-ray binary. The X-ray luminosity of the nuclear source suggests the massive BH is radiating significantly below its Eddington limit (~10^-6 L_Edd), and the soft spectrum resembles other weakly accreting massive BHs including Sagittarius A*. Analysis of the X-ray light curve of the nucleus reveals the tentative detection of a ~9-hour periodicity, although additional observations are required to confirm this result. Our study highlights the need for sensitive high-resolution X-ray observations to probe low-level accretion, which is the dominant mode of BH activity throughout the Universe.