Observing the galactic underworld: predicting photometry and astrometry from compact remnant microlensing events

D Sweeney, P Tuthill, A Krone-Martins… - Monthly Notices of …, 2024 - academic.oup.com
Monthly Notices of the Royal Astronomical Society, 2024academic.oup.com
Isolated black holes (BHs) and neutron stars (NSs) are largely undetectable across the
electromagnetic spectrum. For this reason, our only real prospect of observing these isolated
compact remnants is via microlensing; a feat recently performed for the first time. However,
characterization of the microlensing events caused by BHs and NSs is still in its infancy. In
this work, we perform N-body simulations to explore the frequency and physical
characteristics of microlensing events across the entire sky. Our simulations find that every …
Abstract
Isolated black holes (BHs) and neutron stars (NSs) are largely undetectable across the electromagnetic spectrum. For this reason, our only real prospect of observing these isolated compact remnants is via microlensing; a feat recently performed for the first time. However, characterization of the microlensing events caused by BHs and NSs is still in its infancy. In this work, we perform N-body simulations to explore the frequency and physical characteristics of microlensing events across the entire sky. Our simulations find that every year we can expect BH, NS, and stellar microlensing events which cause an astrometric shift larger than 2 mas. Similarly, we can expect BH, NS, and stellar microlensing events which cause a bump magnitude larger than 1 mag. Leveraging a more comprehensive dynamical model than prior work, we predict the fraction of microlensing events caused by BHs as a function of Einstein time to be smaller than previously thought. Comparison of our microlensing simulations to events in Gaia finds good agreement. Finally, we predict that in the combination of Gaia and GaiaNIR data there will be BH and NS events creating a centroid shift larger than 1 mas and BH and NS events causing bump magnitudes >1. Of these, <10 BH and NS events should be detectable using current analysis techniques. These results inform future astrometric mission design, such as GaiaNIR, as they indicate that, compared to stellar events, there are fewer observable BH events than previously thought.
Oxford University Press