E\"otv\"os Experiments with Supermassive Black Holes

TL;DR

This paper uses the positions of central black holes in elliptical galaxies to test the strong equivalence principle, setting constraints on potential violations of gravitational theory.

Contribution

It introduces a novel method to constrain the strong equivalence principle using black hole locations in galaxies, with current limits and potential improvements discussed.

Findings

Constraints on violation parameter η_N < 0.68 from M87.

High stellar concentration in M32 weakens the constraints.

Better astrometry could significantly improve the constraints.

Abstract

By examining the locations of central black holes in two elliptical galaxies, M\,32 and M\,87, we derive constraints on the violation of the strong equivalence principle for purely gravitational objects, i.e. black holes, of less than about two-thirds, $\eta_N<0.68$ from the gravitational interaction of M\,87 with its neighbours in the Virgo cluster. Although M\,32 appears to be a good candidate for this technique, the high concentration of stars near its centre substantially weakens the constraints. On the other hand, if a central black hole is found in NGC 205 or one of the other satellite ellipticals of M\,31, substantially better constraints could be obtained. In all cases the constraints could improve dramatically with better astrometry.