Session H17: Black Hole Ringdown II

Assessing the Inspiral-Merger-Ringdown Consistency Test of General Relativity

The inspiral-merger-ringdowm (IMR) consistency test has become a standard test of general relativity (GR) for signals analyzed by the LIGO-Virgo-KAGRA Colloboration. This test is based on the idea that all the loss in the mass-energy of the binary throughout coalescence should be predicted completely by standard GR. If the observed gravitational waves (GW) lose/retain more mass-energy than expected, this would result in a discrepancy in the final estimated parameters for each portion of the signal. In this talk, we assess the limits of this test by (1) exploring systematic errors by injecting and recovering with different state-of-the-art GW models and (2) simulating signals using non-standard GR numerical relativity simulations. To gain a greater understanding, we simulate multiple of these signals across different parts of parameter space.   

Visualization of frequency structures in gravitational wave signals

The frequency evolution of gravitational wave signals from the merger of compact binaries follows a slow build-up during the inspiral that peaks at merger, forming the characteristic "chirp" pattern in the signal's time-frequency map. Herein we introduce a framework for localizing further characteristic structures in the time-frequency space of gravitational wave signals using the continuous wavelet transform. We consider two example cases containing specific patterns in the postmerger stage of the signal that are rich with information on the source's physical nature: highly-inclined black hole binaries with asymmetric mass ratio, and neutron star binaries with postmerger remnant oscillations. It is demonstrated that the choice of quality factor Q plays a central role in distinguishing the postmerger features from that of the inspiral, with black hole systems preferring lower Q and neutron star systems preferring higher Q. To increase the detectability of the neutron star postmerger, we also explore stacking time-frequency maps from multiple events.   

Visualizing the black hole postmerger gravitational wave emission profile and horizon geometry

The gravitational waves produced by binary black hole systems with an asymmetric mass ratio exhibit a characteristic double-chirp pattern when viewed from a highly inclined orientation. These chirp patterns are composed of mixed higher-order modes produced during the postmerger stage, resulting from regions of high curvature on the distorted black hole horizon. Herein we utilize a parameterization of the double-chirp pattern using the continuous wavelet transform to map its direction of maximal emission on the sky of the final black hole. It is demonstrated that both the intrinsic properties of the system (mass ratio, spin), and the modal composition of the waveform have distinct impacts on the direction of emission and morphology of the maximal double-chirp pattern. Additionally, the application of this technique towards mapping the geometry of the final black hole horizon is discussed.   

Constraining binaries of black hole mimickers using gravitational waves

There are various theoretical proposals for objects that are massive and compact enough to be mistaken for black holes observationally, e.g., boson stars. Binaries of such objects can be distinguished from binaries of black holes using gravitational wave (GW) observations. In particular, the inspiral signal from a binary of black hole mimickers has imprints of the objects' nonzero tidal deformabilities and non-black hole spin-induced multipole moments. Thus, one can use constraints on these effects to constrain properties of black hole mimickers that could produce GW signals identified as coming from binary black holes (BBHs). However, one has to exclude the less well-modeled post-inspiral signal from this analysis. We show that one can recover the true parameters of black hole mimicker-like signals by self-consistently restricting to the low-frequency portion of the signal. Here we perform the analysis using an extension of the IMRPhenomXP precessing BBH waveform model with additions in the phase of post-Newtonian tidal and spin-induced multipole terms, including the fmtidal model for dynamical tides. We use TEOBResumS + numerical relativity hybrid binary neutron star waveforms scaled to BBH-like masses to test the analysis.   

Constraints on exotic compact objects and scalar fields from gravitational-wave observations

In the gravitational-wave emission from a binary merger, the late part of the signal is produced by the single remnant object as it settles down from its perturbed state.

This signal allows to probe directly the nature of the remnant object.

In black hole spectroscopy, we measure the characteristic spectrum of modes expected for black holes in general relativity, facilitating tests of its predictions.

Additional post-merger signals may reveal the final object to be a more exotic alternative or deviations from general relativity.

If scalar fields are present around a black hole, they may couple to and drive gravitational wave modes with their characteristic frequency.

We search for such signals in observed data to constrain the presence of these scalar fields and their coupling, and predict future prospects using third-generation instruments.

If instead of a black hole the final object is one of several proposed alternatives, characteristic signatures may be present in the post-merger emission.

A horizonless compact object would at late times emit a modified spectrum of weak but long-lived modes following the initial unmodified signal.

With methods adapted to this type of signal, we analyse data from the most promising detections, placing strict bounds on the location of possible deviations from the Kerr geometry.

For a compact object consisting of fluid matter, r-mode oscillations could lead to a similar long-lived signal, and we apply the developed methods to constrain the corresponding fluid's properties.   

Using Entropy to Analyze LIGO Black Holes

By connecting gravitational waves and entropy with the first law of black hole mechanics, we can obtain the entropy of black holes from LIGO-Virgo-KAGRA (LVK) data. We impose thermodynamical constraints based on General Relativity (GR) and the second law of thermodynamics that mergers between two black holes, as an irreversible natural process, will increase the entropy of the universe. We construct a novel framework called BRAHMA to infer the properties and astrophysical implications of binary black hole mergers in LVK. We apply the framework to 10 binary black hole merger events reported by LVK Collaboration. In doing so, we obtain new strong astrophysical insights into the origins of black holes for GW190521 and GW191109, two of the heaviest black hole merger events. For GW191109, the highly negative effective spin does not comply with the uniform distribution of circular binary black hole mergers. The uniform prior imposed increases the effective spin to ~0.2, which is consistent with most gravitational wave black hole populations. Constraints from GR only increase the effective spin slightly, showing black holes with highly negative effective spin still comply with GR. By imposing the constraints from entropy, we also independently prove the existence of black holes inside the pair-instability supernovae mass gap.

Meanwhile, we also perform a systematic investigation of the consistency between phenomenological waveform and ringdown models. Although the NRSur7dq4 waveform generated from numerical relativity is not available for all events, it is proved to be most consistent with entropy. Kerr₂₂₁ was the most consistent ringdown model across all events. To ensure that every dataset has over 10% of data remaining after imposing the constraints, a filtering cut between 75% and 80% is discovered to be optimal, which is significantly lower than the 90% confidence interval of LIGO detection.   

Constraining Nonviolent Nonlocality by Stacking Gravitational Wave Events

Gravitational waves carry information about the structure of the black hole constituents. Giddings' nonviolent nonlocality proposes that the quantum information is transmitted by soft modes in the black hole's atmosphere. In contrast to firewalls, these quantum fluctuations would be spread out over a larger distance range — up to a Schwarzschild radius away. In this talk, we will calculate the waveform of such a binary black hole by modifying EOBNRv2. This waveform will exhibit random deviations, which is particularly evident in the plunge phase. Since this effect does not have a leading order PN term, we will construct an optimal method for hierarchical detection using principal component analysis. Even though there is not an optimal PN deformation dephasing term, we will estimate the constraint on nonviolent nonlocality from O3 data using a new method.