A re-analysis of the isolated black hole candidate OGLE-2011-BLG-0462/MOA-2011-BLG-191

TL;DR

This paper re-analyzes the isolated black hole candidate OGLE-2011-BLG-0462/MOA-2011-BLG-191 using new data and improved methods, confirming its mass as approximately 6 solar masses and highlighting the potential of future space telescopes for black hole studies.

Contribution

The study provides a revised mass measurement of the black hole candidate using updated datasets and analysis techniques, clarifying previous disputes and demonstrating the potential of upcoming telescopes for black hole population studies.

Findings

Revised black hole mass of approximately 6 solar masses.

Significant differences in astrometry compared to previous analyses.

Future space telescopes can measure hundreds of isolated black hole masses.

Abstract

There are expected to be $\sim 10^8$ isolated black holes (BHs) in the Milky Way. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with a mass measurement to date. However, its mass is disputed: Lam et al. (2022a,b) measured a lower mass of $1.6 - 4.4 M_\odot$, while Sahu et al. (2022); Mr\'{o}z et al. (2022) measured a higher mass of $5.8 - 8.7 M_\odot$. We re-analyze OB110462, including new data from the Hubble Space Telescope (HST) and re-reduced Optical Gravitational Lensing Experiment (OGLE) photometry. We also re-reduce and re-analyze the HST dataset with newly available software. We find significantly different ($\sim 1$ mas) HST astrometry than Lam et al. (2022a,b) in the de-magnified epochs due to the amount of positional bias induced by a bright star $\sim$0.4 arcsec from OB110462. After modeling the updated photometric and astrometric datasets, we find the lens of OB110462 is a $6.0^{+1.2}_{-1.0} M_\odot$ BH. Future observations with the Nancy Grace Roman Space Telescope, which will have an astrometric precision comparable or better to HST but a field of view $100\times$ larger, will be able to measure hundreds of isolated BH masses via microlensing. This will enable the measurement of the BH mass distribution and improve understanding of massive stellar evolution and BH formation channels.