Evidence of large recoil velocity from a black hole merger signal

Abstract

The final black hole left behind after a binary black hole merger can attain a recoil velocity, or a "kick", reaching values up to 5000 km/s. This phenomenon has important implications for gravitational wave astronomy, black hole formation scenarios, testing general relativity, and galaxy evolution. We consider the gravitational wave signal from the binary black hole merger GW200129_065458 (henceforth referred to as GW200129), which has been shown to exhibit strong evidence of orbital precession. Using numerical relativity surrogate models, we constrain the kick velocity of GW200129 to v f ∼ 1542 +747 −1098 km/s or v f 698 km/s (one-sided limit), at 90% credibility. This marks the first identification of a large kick velocity for an individual gravitational wave event. Given the kick velocity of GW200129, we estimate that there is a less than 0.48% (7.7%) probability that the remnant black hole after the merger would be retained by globular (nuclear star) clusters. Finally, we show that kick effects are not expected to cause biases in ringdown tests of general relativity for this event, although this may change in the future with improved detectors.Introduction.-When two black holes (BHs) orbit each other, they emit gravitational waves (GWs) which carry away energy and angular momentum. This causes the orbit to shrink in a runaway process that culminates in the merger of the BHs into a single remnant BH. At the same time, the GWs can also carry away linear momentum from the binary, shifting its center of mass in the opposite direction [1]. Most of the linear momentum is lost near the merger [2], resulting in a recoil or "kick" velocity imparted to the remnant BH.Kicks are particularly striking for precessing binaries, in which the component BH spins are tilted with respect to the orbital angular momentum. For these systems, the spins interact with the orbital angular momentum as well as with each other, causing the orbital plane to precess [3]. Numerical relativity (NR) simulations revealed that the kick velocities for precessing binaries can reach values up to ∼ 5000 km/s [4-6], large enough to be ejected from any host galaxy [7].Kicks have important implications for BH astrophysics. Following a supermassive BH merger, the remnant BH can be displaced from the galactic center or ejected entirely [7], impacting the galaxy's evolution [8], fraction of galaxies with central supermassive BHs [9], and event rates [10] for the future LISA mission [11]. For stellar-mass BHs like those observed by LIGO [12] and Virgo [13], kicks can limit the formation of heavy BHs. BH masses greater than ∼65M are disfavored by supernova simulations [14,15], but have been seen in GW events [16][17][18]. This could be

Hierarchical Merger of Primordial Black Holes in Dwarf Galaxies

“…For example, since the DGs are faint with low stellar mass, we have neglected the effect of mergers on stars, but a more detailed study contemplating such collisions would include electromagnetic signals which will constrain the parameters of the model. The recoil velocity of the product BH after a merger event is also an ingredient to be included in future studies [74,75,76]. In the meantime, our results indicate that a series of sequential mergers may take place at the cores of DGs.…”

Inconsistent black hole kick estimates from gravitational-wave models

“…Several methods have been proposed to discuss the detectability of kicks in GW events [28][29][30]. Among the current GW observations, GW190814 shows the most informative kick estimate from the events of the second GW transient catalog (GWTC-2) [31], while GW200129_06 5458 shows support for a large kick velocity [32]. However, the kick's subtle signatures have not been precisely measured so far.…”

“…We evaluate the accuracy of four waveform models which are used in current GW data analysis studies. We also analyse the performance of the NR Sur fit [44], recently used to make the first measurement of a large kick velocity in an observed GW signal [32]. By exploiting the features of the kick, we create a set of diagnostic tests that can be applied to any waveform model to identify modelling inaccuracies over the parameter space.…”

A fully precessing higher-mode surrogate model of effective-one-body waveforms

“…As detector sensitivities improve and the number of observed BBHs increases, we are more likely to observe rare and unexpected events such as BBHs with asymmetric masses [18,19], or evidence for precession and merger kicks arising from spins misaligned with the orbital angular momentum [5,[20][21][22], or intermediate mass black holes (BHs) [23]. The wealth of information provided by precessing compact binary coalescences (CBCs) is invaluable to help us identify astrophysical formation channels [24,25].…”