Matched filtering is a popular data analysis framework used to search for gravitational wave signals emitted by compact object binaries. The templates used in matched filtering searches are constructed predominantly from the quadrupolar mode because
this mode is the energetically most dominant channel. However, for highly precessing binaries or binaries with moderately large mass ratios, significant power is also carried by higher-order modes. We investigate how the inclusion of higher modes in the templates increases the prospects for detecting gravitational waves. Specifically, we use numerical relativity waveforms from the late inspiral and coalescence of binary black holes to identify mode hierarchies that cover the sky of binary orientations. We show that the ordering in these hierarchies depends on the characteristics of the binary system and the mode strengths. Our study demonstrates that detecting moderately high precessing or unequal mass binaries requires the inclusion of higher modes in the templates banks.
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 quasi-circular inspirals to more energeti
c 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 $a/M_h approx 0.99pm 0.01$ 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 $lbrace M_h/M, a/M_h rbrace$ ~spiraling around the values $lbrace hat M_h/M, hat a/M_h rbrace$ of a {it golden} black hole. Specifically, $(M_h-hat M_h)/M propto e^{pm B,phi}cos{phi}$ and $(a-hat a)/M_h propto e^{pm C,phi}sin{phi}$, with $phi$ a monotonically growing function of the initial orbital angular momentum. We find that the values of the parameters for the emph{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 quasi-circular inspiral.
