Improve the identification of accreting isolated black holes

Establish reliable methods for distinguishing isolated black holes accreting from the interstellar medium from other Galactic X-ray sources through spectral modeling and multiwavelength observations.

Background

The predicted number of X-ray-bright isolated black holes depends strongly on assumptions about radiative efficiency and hot accretion flows, but a flux prediction alone does not establish an observational identification. The Galactic X-ray sky contains neutron stars and other accreting systems, especially toward the Galactic center. The paper therefore identifies source discrimination and dynamical characterization as an unresolved observational problem.

References

Source identification therefore remains a major challenge for future observations.

— A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes  (2609.29211 - He et al., 24 Sep 2026) in Section 5.2, “Detection of IBHs”