Eötvös experiments with supermassive black holes

By examining the locations of central black holes in two ellipticalgalaxies, M32 and M87, we derive constraints on the violation of thestrong equivalence principle for purely gravitational objects, i.e.black holes, of less than about two-thirds, ηN < 0.68from the gravitational interaction of M87 with its neighbours in theVirgo cluster. Although M32 appears to be a good candidate for thistechnique, the high concentration of stars near its centre substantiallyweakens the constraints. On the other hand, if a central black hole isfound in NGC 205 or one of the other satellite ellipticals of M31,substantially better constraints could be obtained. In all cases, theconstraints could improve dramatically with better astrometry.