Induced spins from scattering experiments of initially nonspinning black holes

Abstract

When two relativistically boosted, nonspinning black holes pass by one another on a scattering trajectory, we might expect the tidal interaction to spin up each black hole. We present the first exploration of this effect, appearing at fourth post-Newtonian order, with full numerical relativity calculations. The basic set up for the calculations involves two free parameters: the initial boost of each black hole and the initial angle between their velocity vectors, with zero angle corresponding to a head-on trajectory. To minimize gauge effects, we measure final spins only if the black holes reach a final separation of at least 20M . Fixing the initial boost, we find that as the initial angle decreases toward the scattering/non-scattering limit, the spin-up grows nonlinearly. In addition, as initial boosts are increased from 0.42c to 0.78c, the largest observed final dimensionless spin on each black hole increases nonlinearly from 0.02 to 0.20. Based on these results, we conclude that much higher spin-ups may be possible with larger boosts, although achieving this will require improved numerical techniques.

Effective-one-body waveforms from dynamical captures in black hole binaries

“…The model of [7] is based on geodesic motion on a Kerr black hole spacetime augmented by leadingorder Newtonian-like radiation reaction, then complemented by an effective model for a (quasi-circular) ring-down informed by NR simulations 1 . Similarly, numerical relativity (NR) studies of BBH mergers from dynamical capture conducted thus far are only few [12][13][14] and limited to nonspinning binaries.…”

“…Moreover, the existing NR results, e.g. [7,12,13] are not expressed using gauge-invariant observables and so it is impossible to extract any kind of information that could be directly compared with our model. Instead, we will provide an up-to-date comparison with the measured scattering angle of Ref.…”

21-cm constraints on spinning primordial black holes

“…In addition to Hawking radiation, there could also be other physical processes that can change the mass and spin of PBHs, most notably BH mergers [67,68] and accretion [69]. It's possible that PBH spin can also have extended distributions [49,54,[67][68][69][70][71][72], but these complicated scenarios are beyond the scope of this paper, so we restrict our discussions to PBHs born with the same initial spin.…”

Black hole induced spins from hyperbolic encounters in dense clusters

“…The parameter file that has been used is based on the one used in Ref. [13]. It is similar to the examples for binary black holes provided with the Einstein Toolkit, but with some key modifications that allow increasing the initial separation up to 100 GM/c 2 .…”

“…A numerical exploration of this effect was done by Nelson et al in Ref. [13], proving that the induced spin could be relevant and reach at least χ ≈ 0.2 for equal-mass cases.…”