Searching for Isolated Black Hole Candidates within 15 pc of the Solar System in Gaia DR3

TL;DR

This study searches Gaia DR3 data for isolated black hole candidates within 15 parsecs, finding five potential sources but concluding they are unlikely to be black holes accreting from the interstellar medium.

Contribution

First systematic search for isolated black hole candidates in Gaia DR3 within 15 pc, combining astrometric and electromagnetic data to identify and evaluate potential candidates.

Findings

Identified five candidate sources near the Galactic plane.

Candidates likely spurious due to crowding or binarity effects.

Infrared and radio observations suggest candidates are not accreting black holes.

Abstract

Theoretical models predict that the Galaxy hosts $10^8$-$10^9$ black holes formed from the complete gravitational collapse of heavy stars and that most of these black holes are isolated, without any companion. Within 15 pc of the Solar System ($\sim 50$ ly), there may be a few black holes. If located inside one of the Local Interstellar Clouds - which occupy 5-20% of this local volume - an isolated black hole could produce detectable electromagnetic emission via accretion from the interstellar medium, given the capabilities of current or near-future observatories. However, precise predictions remain challenging due to large uncertainties in the expected accretion spectra. Outside these clouds, the accretion rate would be too low; according to our models, the resulting electromagnetic flux is well below the detection thresholds of current and near-future observational facilities. While astrometric detection via gravitational perturbation of nearby stars is conceivable, the local stellar density is too low for this method to be realistically successful. We have searched the Gaia DR3 catalog for candidate isolated black holes accreting from the interstellar medium and identified five sources. All candidates lie close to the Galactic plane, making them likely spurious astrometric solutions, for instance caused by unmodelled background sources (crowding) and/or unmodelled binarity. Our search for infrared and radio emission from these sources further suggests that they are unlikely to be black holes accreting from the interstellar medium.