Repeated ringing of black holes: Quasinormal bursts from highly eccentric, extreme mass-ratio binaries

Nur E M Rifat,Lior M Burko,Gaurav Khanna

doi:10.1103/physrevresearch.1.033150

Nur E M Rifat, Lior M Burko + Show 1 more

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https://doi.org/10.1103/physrevresearch.1.033150

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Abstract

Recent studies of scalar and gravitational waveforms from high-eccentricity, extreme mass-ratio black hole binaries show the presence of quasi-normal bursts (QNB) -- lingering high frequency decaying oscillations (also known as ``wiggles'') -- soon after each periapsis passage. One puzzle associated with these QNB is that in the case of a nearly-extreme rotating central black hole the frequency of the QNB has been found to be in a range which is lower than the corresponding range of relevant quasi-normal modes. We reproduce these results using a different approach and perform a detailed analysis to find evidence for the resolution of the puzzle and for the origin of the QNB. We find that the QNB frequency as measured at future null infinity evolves in (retarded) time and approaches the dominant quasi-normal frequency exponentially in time. We also show that the QNB amplitude decays inversely in (retarded) time. We discuss the time dependence of both the QNB waveform frequency and its amplitude and argue that this behavior arises as a result of the excitation of many quasi-normal overtones and the summation thereof.

Highlights

When the periapsis of the orbit of a compact object around a massive black hole gets close to the light ring of the latter, the compact object can excite the massive black hole’s quasinormal modes (QNMs), which results in repeated bursts of high-frequency gravitational waves, known as “wiggles,” with each periapsis passage [1,2]
We suggest that the full explanation of the effect we consider in this work lies in the behavior of the QNM overtones of a nearly extreme Kerr black hole
We find that the oscillations in ψ42,2 start shortly before periapsis passage and are made of two main parts: first, high-amplitude oscillations that are related to the whirl part of the orbit [9], followed by the quasinormal bursts (QNBs) (“wiggle”) part, lingering high-frequency oscillations that decay slowly until close to the periapsis passage

Summary

INTRODUCTION

When the periapsis of the orbit of a compact object around a massive black hole gets close to the light ring of the latter, the compact object can excite the massive black hole’s quasinormal modes (QNMs), which results in repeated bursts of high-frequency gravitational waves, known as “wiggles,” with each periapsis passage [1,2]. While excitations by a particle of QNMs had been observed before (first seen for a marginally bound particle which is scattered or absorbed by a Kerr black hole [6]), an unexpected feature emerges when the central black hole spins at a nearly extreme rate: The frequency of the QNB waveform lies in a range that is lower than the relevant QNM frequencies [1] This curious phenomenon has been observed in the self-force on the compact object [5] and in the shear response of the central black hole’s horizon [4]. We show that precisely the same effect is present in a much simpler, source-free scalar wave evolution in nearly extreme Kerr space-time background This result suggests that the explanation for the time dependence of the frequency of the QNB waveform is purely due to the quasinormal spectrum of. We suggest that the full explanation of the effect we consider in this work lies in the behavior of the QNM overtones of a nearly extreme Kerr black hole

POINT-PARTICLE BLACK-HOLE PERTURBATION THEORY

NUMERICAL RESULTS

CONCLUDING REMARKS