Eccentric binary black-hole mergers: The transition from inspiral to plunge in general relativity

TL;DR

This paper investigates the transition from inspiral to plunge in non-spinning black-hole binaries, analyzing gravitational waveforms and final spins to understand the limits of black hole mergers and their compliance with cosmic censorship.

Contribution

It provides detailed simulations of eccentric black-hole mergers, identifying the critical angular momentum for transition and proposing limits on the remnant spin consistent with cosmic censorship.

Findings

Transition from inspiral to plunge occurs at L ≈ 0.8 M^2.

Maximum remnant spin parameter j ≈ 0.724.

No merger can produce a black hole violating cosmic censorship.

Abstract

We study the transition from inspiral to plunge in general relativity by computing gravitational waveforms of non-spinning, equal-mass black-hole binaries. We consider three sequences of simulations, starting with a quasi-circular inspiral completing 1.5, 2.3 and 9.6 orbits, respectively, prior to coalescence of the holes. For each sequence, the binding energy of the system is kept constant and the orbital angular momentum is progressively reduced, producing orbits of increasing eccentricity and eventually a head-on collision. We analyze in detail the radiation of energy and angular momentum in gravitational waves, the contribution of different multipolar components and the final spin of the remnant. We find that the motion transitions from inspiral to plunge when the orbital angular momentum L=L_crit is about 0.8M^2. For L<L_crit the radiated energy drops very rapidly. Orbits with L of about L_crit produce our largest dimensionless Kerr parameter for the remnant, j=J/M^2=0.724. Generalizing a model recently proposed by Buonanno, Kidder and Lehner to eccentric binaries, we conjecture that (1) j=0.724 is the maximal Kerr parameter that can be obtained by any merger of non-spinning holes, and (2) no binary merger (even if the binary members are extremal Kerr black holes with spins aligned to the orbital angular momentum, and the inspiral is highly eccentric) can violate the cosmic censorship conjecture.