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Supermassive recoil velocities for binary black-hole mergers with antialigned spins

J. A. Gonzalez, M. D. Hannam, U. Sperhake, B. Brugmann, S. Husa

TL;DR

This paper demonstrates that binary black-hole mergers with equal masses and anti-aligned spins in the orbital plane can produce gravitational-recoil velocities as large as $v_{kick} \approx 2.5\times 10^3$ km s$^{-1}$, far exceeding prior expectations. Using two independent numerical-relativity codes with the moving-puncture method, the authors compute the recoil from the radiated momentum via $\Psi_4$ and show robust, fourth-order convergent results with controlled extraction-radius errors. The findings imply that such kicks can eject black holes from even giant galaxies, influencing black-hole demographics, galaxy cores, and high-redshift growth scenarios, though the astrophysical likelihood requires broader parameter surveys. The work is complemented by independent follow-up studies that confirm the plausibility of large kicks, reinforcing the significance of extreme spin configurations for astrophysical black-hole populations.

Abstract

Recent calculations of the recoil velocity in binary black hole mergers have found the kick velocity to be of the order of a few hundred km/s in the case of non-spinning binaries and about $500 $km/s in the case of spinning configurations, and have lead to predictions of a maximum kick of up to $1300 $km/s. We test these predictions and demonstrate that kick velocities of at least $2500 $km/s are possible for equal-mass binaries with anti-aligned spins in the orbital plane. Kicks of that magnitude are likely to have significant repercussions for models of black-hole formation, the population of intergalactic black holes and the structure of host galaxies.

Supermassive recoil velocities for binary black-hole mergers with antialigned spins

TL;DR

This paper demonstrates that binary black-hole mergers with equal masses and anti-aligned spins in the orbital plane can produce gravitational-recoil velocities as large as km s, far exceeding prior expectations. Using two independent numerical-relativity codes with the moving-puncture method, the authors compute the recoil from the radiated momentum via and show robust, fourth-order convergent results with controlled extraction-radius errors. The findings imply that such kicks can eject black holes from even giant galaxies, influencing black-hole demographics, galaxy cores, and high-redshift growth scenarios, though the astrophysical likelihood requires broader parameter surveys. The work is complemented by independent follow-up studies that confirm the plausibility of large kicks, reinforcing the significance of extreme spin configurations for astrophysical black-hole populations.

Abstract

Recent calculations of the recoil velocity in binary black hole mergers have found the kick velocity to be of the order of a few hundred km/s in the case of non-spinning binaries and about km/s in the case of spinning configurations, and have lead to predictions of a maximum kick of up to km/s. We test these predictions and demonstrate that kick velocities of at least km/s are possible for equal-mass binaries with anti-aligned spins in the orbital plane. Kicks of that magnitude are likely to have significant repercussions for models of black-hole formation, the population of intergalactic black holes and the structure of host galaxies.

Paper Structure

This paper contains 4 sections, 3 figures, 1 table.

Table of Contents

  1. Introduction.---
  2. Numerical framework.---
  3. Results.---
  4. Astrophysical relevance.---

Figures (3)

  • Figure 1: Upper panel: the $z$-component of the recoil for model MI as a function of time for grid resolutions $h_1=1/36$, $h_2=1/44$ and $h_3=1/48$. Lower panel: the differences scaled for fourth-order convergence.
  • Figure 2: Recoil for model MI as a function of time for different extraction radii. Extrapolation to $r\to\infty$ yields a magnitude of $2450\,$km/s with an error estimate of $4.5\,\%$. Also shown is the kick from model MII using Bam.
  • Figure 3: Coordinate positions of the black-hole punctures for model MII up to $t = 180$. The black holes move out of the original plane and after merger the final black hole receives a kick in the negative $z$-direction.