Final mass and maximum spin of merged black holes and the golden black hole

We present results on the mass and spin of the final black hole from mergers of equal mass, spinning black holes. The study extends over a broad range of initial orbital configurations, from direct plunges to quasicircular inspirals to more energetic orbits (generalizations of Newtonian elliptical orbits). It provides a comprehensive search of those configurations that maximize the final spin of the remnant black hole. We estimate that the final spin can reach a maximum spin a/Mh≅0.99±0.01 for extremal black hole mergers. In addition, we find that, as one increases the orbital angular momentum from small values, the mergers produce black holes with mass and spin parameters (Mh/M,a/Mh) spiraling around the values (M-circumflexh/M,a-circumflex/Mh) of a golden black hole. Specifically, (Mh-M-circumflexh)/M∝e±Bφcosφ and (a-a-circumflex)/Mh∝e±Cφsinφ, with φ a monotonically growing function of the initial orbital angular momentum. We find that the values of the parameters for the golden black hole are those of the final black hole obtained from the merger of a binary with the corresponding spinning black holes in a quasicircular inspiral.