Determine the mass function of isolated black holes

Determine the mass function governing isolated stellar-origin and dark-matter black holes in the mass range 3–5000 solar masses, so that microlensing event populations and detection rates can be modeled without relying on assumed power-law mass functions.

Background

The study simulates microlensing events caused by isolated black holes (IBHs) toward the Large and Small Magellanic Clouds. Because the number of detected isolated stellar-origin or dark-matter IBHs is expected to be small, the paper states that their mass function is not empirically established.

To proceed with its Monte Carlo calculations, the paper adopts four illustrative power-law mass functions, with indices ranging from 0 to 2. A physically validated mass function would be needed to convert the predicted detection efficiencies and event rates into more reliable expectations for Rubin Observatory observations.

References

The numbers of detected and isolated SO or DM IBHs (compact and massive objects in the form of MACHOs, primordial BHs, etc.) are low and there is no known mass function for them.

— Detection and Characterization of Microlensing Events due to Isolated Black Holes towards the Magellanic Clouds in the Rubin Observations  (2608.16448 - Sajadian et al., 17 Aug 2026) in Section 3, subsection “Microlensing due to IBHs towards Magellanic Clouds”