Industrial-Scale Mass Measurements of Isolated Black Holes

TL;DR

This paper proposes a method combining ground-based microlensing surveys, space-based parallax observations, and interferometry to measure the masses of isolated black holes at an industrial scale with high precision.

Contribution

It introduces a comprehensive approach for large-scale, precise mass measurements of isolated black holes using combined observational techniques and detailed simulation analyses.

Findings

Achieves mass measurement precision down to 12 solar masses.

Effectively excludes spurious parallax solutions in black hole microlensing events.

Provides strategies to resolve degeneracies with additional VLTI measurements.

Abstract

I show that industrial-scale mass measurement of isolated black holes (BHs) can be achieved by combining a high-cadence, wide-field microlensing survey such as KMTNet, observations from a parallax satellite in solar orbit, and VLTI GRAVITY+ interferometry. I show that these can yield precision measurements of microlens parallaxes down to $\pi_{\rm E}\sim 0.01$ and Einstein radii down to $\theta_{\rm E}\sim 1\,$mas. These limits correspond to BH masses $M\sim 12\,M_\odot$, deep in the Galactic bulge, with lens-source separations of $D_{LS}\sim 0.6\,$kpc, and they include all BHs in the Galactic disk. I carry out detailed analyses of simulations that explore many aspects of the measurement process, including the decisions on whether to carry out VLTI measurements for each long-event candidate. I show that the combination of ground-based and space-based light curves of BH events will automatically exclude the spurious "large parallax" solutions that arise from the standard (Refsdal 1966) analysis, except for the high-magnification events, for which other methods can be applied. The remaining two-fold degeneracy can always be broken by conducting a second VLTI measurement, and I show how to identify the relatively rare cases that this is required.