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There are expected to be $\sim 10^8$ isolated black holes (BHs) in the MilkyWay. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with amass 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 $5.8 - 8.7 M_\odot$. Were-analyze OB110462, including new data from the Hubble Space Telescope (HST)and re-reduced Optical Gravitational Lensing Experiment (OGLE) photometry. Wealso re-reduce and re-analyze the HST dataset with newly available software. Wefind significantly different ($\sim 1$ mas) HST astrometry than Lam et al.(2022a,b) in the de-magnified epochs due to the amount of positional biasinduced by a bright star $\sim$0.4 arcsec from OB110462. After modeling theupdated 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 RomanSpace Telescope, which will have an astrometric precision comparable or betterto HST but a field of view $100\times$ larger, will be able to measure hundredsof isolated BH masses via microlensing. This will enable the measurement of theBH mass distribution and improve understanding of massive stellar evolution andBH formation channels.

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