On minor black holes in galactic nuclei

TL;DR

This paper explores the presence and observational signatures of minor black holes in galactic nuclei, suggesting they could explain certain low luminosity AGN phenomena and serve as electromagnetic counterparts to gravitational wave events.

Contribution

It provides a detailed discussion of how minor black holes can produce observable signatures in galactic nuclei, linking ULXs to LINERs and transition objects, and discusses observational constraints and future prospects.

Findings

Optical line ratios in LINERs can be explained by ULX ionizing radiation.

Minor black holes may account for low luminosity AGN phenomena.

Potential electromagnetic counterparts to gravitational wave signals from inspiraling black holes.

Abstract

Small and intermediate mass black holes should be expected in galactic nuclei as a result of stellar evolution, minor mergers and gravitational dynamical friction. If these minor black holes accrete as X-ray binaries or ultra-luminous X-ray sources, and are associated with star formation, they could account for observations of many low luminosity AGN or LINERs. Accreting and inspiralling intermediate mass black holes could provide a crucial electromagnetic counterpart to strong gravitational wave signatures, allowing tests of strong gravity. Here we discuss observational signatures of minor black holes in galactic nuclei and we demonstrate that optical line ratios observed in LINERs or transition-type objects can be produced by an ionizing radiation field from ULXs. We conclude by discussing constraints from existing observations as well as candidates for future study.