Secular Evolution of Compact Binaries Near Massive Black Holes: Gravitational Wave Sources and Other Exotica

Abstract

The environment near super massive black holes (SMBHs) in galactic nuclei contains a large number of stars and compact objects. A fraction of these are likely to be members of binaries. Here we discuss the binary population of stellar black holes and neutron stars near SMBHs and focus on the secular evolution of such binaries, due to the perturbation by the SMBH. Binaries with highly inclined orbits in respect to their orbit around the SMBH are strongly affected by secular Kozai processes, which periodically change their eccentricities and inclinations (Kozai-cycles). During periapsis approach, at the highest eccentricities during the Kozai-cycles, gravitational wave emission becomes highly efficient. Some binaries in this environment can inspiral and coalesce at timescales much shorter than a Hubble time and much shorter than similar binaries which do not reside near a SMBH. The close environment of SMBHs could therefore serve as catalyst for the inspiral and coalescence of binaries, and strongly affect their orbital properties. Such compact binaries would be detectable as gravitational wave (GW) sources by the next generation of GW detectors (e.g. advanced-LIGO). About 0.5 % of such nuclear merging binaries will enter the LIGO observational window while on orbit that are still very eccentric (e 0.5). The efficient gravitational wave analysis for such systems would therefore require the use of eccentric templates. We also find that binaries very close to the SMBH could evolve through a complex dynamical (non-secular) evolution leading to emission of several GW pulses during only a few yrs (though these are likely to be rare). Finally, we note that the formation of close stellar binaries, X-ray binaries and their merger products could be induced by similar secular processes, combined with tidal friction rather than GW emission as in the case of compact object binaries.

Double-averaging can fail to characterize the long-term evolution of Lidov–Kozai Cycles and derivation of an analytical correction

“…Antonini & Perets 2012;Bode & Wegg 2014;. In this paper we demonstrate that the short-term errors can accumulate over time, and the accumulated errors can significantly affect the long-term evolution of the system especially when the mass of the perturber is comparable or larger than that of the inner binary.…”

“…The effects of the short-term oscillations in Lidov-Kozai cycles were noted before (e.g. Antonini & Perets 2012;Bode & Wegg 2014;. Over a short timescale, If the amplitudes of the short-term oscillations are large enough, they can bring j z to cross zero, which can lead to high eccentricities (see §1 and Bode & Wegg 2014;Antonini et al 2015).…”

Implications of the gravitational wave event GW150914

“…Another possibility that has recently been explored is that a black hole binary in a galactic central region could be considered to be in a triple system with the central supermassive black hole of the galaxy [141,142,143]. There are large uncertainties in the rates, but if black hole binaries are common and if the perturbations to the orbit around the supermassive black hole give the binary many opportunities to be in a Kozai-favorable configuration, rates per volume as high as ∼ 100 Gpc −3 yr −1 might be produced by this mechanism [143].…”

Spin–Orbit Misalignment of Merging Black Hole Binaries with Tertiary Companions

“…The detection of eccentric systems would obviously indicates some dynamical processes at work (e.g., Antonini & Perets (2012); Silsbee & Tremaine (2017)). However, because of the efficient eccentricity damping by gravitational radiation, the vast majority of compact binaries will likely be circular when entering the LIGO sensitivity band regardless of the formation channels.…”