Constraining the mass density of free-floating black holes using razor-thin lensing arcs

Understand

Strong lensing of active galactic nuclei in the radio can result in razor-thin arcs, with a thickness of less than a milli-arcsecond, if observed at the resolution achievable with very long baseline interferometry (VLBI).

• Such razor-thin arcs provide a unique window on the coarseness of the matter distribution between source and observer.
• In this paper, we investigate to what extent such razor-thin arcs can constrain the number density and mass function of `free-floating' black holes, defined as black holes that do not, or no longer, reside at the centre of a galaxy.
• These can be either primordial in origin or arise as by-products of the evolution of super-massive black holes in galactic nuclei.