Triple Black Holes in the Cores of Galaxies

We investigate the evolution of black hole (BH) triples in the cores of galaxies. A triple BH system can be formed when a merger remnant of ellipticals having central BHs merges again with another galaxy. The spiral-in of massive BHs, which are proposed as a candidates for constituents of the dark halo of our Galaxy, can also make a triple BH system in the core of the Galaxy. It has been argued that such a triple system will inevitably result in the ejection of at least one of the BHs by the gravitational slingshot. We will show that such a slingshot is unlikely to occur and that two of the three BHs are likely to merge by gravitational radiation. The final state is the binary of this merged BH and the third BH, which may or may not merge by the combined effect of dynamical friction from the stars in the core and gravitational radiation.