Maximum Gravitational Recoil

Abstract

Recent calculations of gravitational radiation recoil generated during black-hole binary mergers have reopened the possibility that a merged binary can be ejected even from the nucleus of a massive host galaxy. Here we report the first systematic study of gravitational recoil of equal-mass binaries with equal, but counter-aligned, spins parallel to the orbital plane. Such an orientation of the spins is expected to maximize the recoil. We find that recoil velocity (which is perpendicular to the orbital plane) varies sinusoidally with the angle that the initial spin directions make with the initial linear momenta of each hole and scales up to a maximum of ∼ 4000 km s −1 for maximally-rotating holes. Our results show that the amplitude of the recoil velocity can depend sensitively on spin orientations of the black holes prior to merger. Introduction: Generic black-hole-binary mergers will display a rich spectrum of gravitational effects in the last few orbits prior to the formation of the single rotating remnant hole. These effects include spin and orbital plane precession, radiation of mass, linear and angular momentum, as well as spin-flips of the remnant horizon. Thanks to recent breakthroughs in the full non-linear numerical evolution of black-hole-binary spacetimes [1,2,3], it is now possible to accurately simulate the merger process and examine these effects in this highly non-linear regime [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Black-hole binaries will radiate between 2% and 8% of their total mass and up to 40% of their angular momenta, depending on the magnitude and direction of the spin components, during the merger [6,7,8]. In addition, the radiation of net linear momentum by a black-hole binary leads to the recoil of the final remnant hole [19,20,21,22,23,24,25,26,27,28]. This phenomenon can lead to astrophysically important effects [29,30].A non-spinning black-hole binary will emit net linear momentum parallel to its orbital plane if the individual holes have unequal masses. However, the maximum recoil in this case (which occurs when the mass ratio is q ≈ 0.36) is a relatively small ∼ 175 km s −1 [22].The first generic simulation of black-hole binaries with unequal masses and spins was reported in [24]. These black holes displayed spin precession and spin flips, and for the first time, recoil velocities over 400km s −1 , mostly along the orbital angular momentum direction. It was thus found that the unequal spin components to the recoil velocity can be much larger than those due to unequal masses, and that comparable mass, maximally spinning holes with spins in the orbital plane and counter-aligned

Extra-large remnant recoil velocities and spins from near-extremal-Bowen-York-spin black-hole binaries

“…binaries with unequal component masses and spins, and spins not aligned with each other or the orbital angular momentum) was described in Ref. [33], and, based on the results of that study, a semi-empirical formula to estimate the recoil velocities of the remnant black holes was proposed, finding recent confirmation in [35,45,46]. The spin contributions to the recoil velocity are generally larger than those due to the unequal masses, and, in particular, the spin component in the orbital plane has the largest effect [33], leading to a maximum recoil velocity of about 3500 − 4000 km s −1 [35].…”

“…Notably, it has been successfully applied to many-black-hole spacetimes [27,28], and to black-hole-neutron star evolutions [29,30,31,32]. Similarly, the recent discovery of very large merger recoil kicks [33,34,35,36,37,38,39,40] has had a great impact in the astrophysical community, with several groups now seeking for observational traces of such high speed holes as the byproduct of galaxy collisions [41,42,43,44].…”

The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?

“…Recoiling BHs may also result from BH-BH mergers and the associated anisotropic emission of gravitational waves (GW, Peres 1962;Beckenstein et al 1973). The resultant merged BH may receive a kick and be displaced or even ejected from the host galaxy (Merritt et al 2004;Madau & Quataert 2004;Komossa 2012), a process that has been extensively studied with simulations (Campanelli et al 2007;Blecha et al 2011Blecha et al , 2016. Typically, for non-spinning BHs, the expected velocity is of the order of a few hundreds of km s −1 , or less.…”

Long gamma ray bursts from binary black holes

“…For instance, Baker et al (2008) modeled the coalescence of nonspinning BHs with different mass ratios. Also, González et al (2007) and Campanelli et al (2007) studied the cases with general spin orientations. These simulations show that for mergers with BHs of low spins or the spins aligned, the maximum speeds of the kick are below 200 km s −1 .…”