Physics Professor @ U of MS. Specializing in gravity, general relativity, black holes, gravitational waves, numerical relativity
Congratulations to Aniket Khairnar and Subhayu Bagchi on defending their PhDs! We had a double-header defense day, with Aniket in the morning and Subhayu in the afternoon. Three committee members were in common between the two defenses.
Post-Newtonian (PN) theory provides the analytic foundation for modeling the early inspiral of binary black holes. However, as an asymptotic series, successive PN orders do not necessarily improve agreement with the full nonlinear dynamics. While this has been explored in the extreme-mass-ratio limit, comparable-mass systems most relevant to current observations have not been benchmarked as…
Accurate models of merger remnants are increasingly important for gravitational-wave science, including precision tests of gravity with ringdown, inference of black-hole populations, and modeling hierarchical mergers. For eccentric binaries, remnant mass, spin, and recoil carry nontrivial imprints of eccentricity that are both physically informative and more challenging to model, yet remain less…
The name near-identity transformation (NIT) is just shorthand for a specific application of perturbation theory—one which is particularly useful in dynamical systems that have slow and fast timescales. This is not all they can be used for (see e.g. Fumagalli+1 where a NIT is used to remove gauge dependence). What I write below is covered in some standard references but it’s easy enough to rederive…
The Bondi–van der Burg–Metzner–Sachs (BMS) frame of gravitational waves produced by numerical relativity (NR) simulations is crucial for building accurate waveform models. A proper comparison of NR waveforms with other models requires fixing the arbitrary BMS frame. In this work we improve the center-of-mass (CoM) frame fixing for quasicircular, nonprecessing binary systems. Past work approximated…
The photon ring of a Kerr black hole decomposes into a self-similar hierarchy of subrings. Here, we show that this self-similar structure persists in phase space. Moreover, near the photon shell of bound photon orbits, dynamics are controlled by a Lyapunov exponent γ, whose role we highlight by computing the first-return map for light rays close to an unstably bound orbit. Despite an exponential…
We investigate how commonly used parameter definitions in Post-Newtonian (PN) theory compare with those from Numerical Relativity (NR) for binary black hole (BBH) systems. In NR, masses and spins of each companion are measured quasi-locally from apparent horizon geometry, whereas in PN they are attributes of point particles defined via asymptotic matching in body zones. Although these definitions…
The ‘ringdown’ radiation emitted by oscillating black holes has great scientific potential. By carefully predicting the frequencies and amplitudes of black hole quasinormal modes and comparing them with gravitational-wave (GW) data from compact binary mergers we can advance our understanding of the two-body problem in general relativity, verify the predictions of the theory in the regime of strong…
We present a major update to the Simulating eXtreme Spacetimes (SXS) Collaboration’s catalog of binary black hole simulations. Using highly efficient spectral methods implemented in the Spectral Einstein Code SpEC, we have nearly doubled the total number of binary configurations from 2,018 to 3,756. The catalog now densely covers the parameter space with precessing simulations up to mass ratio and…
Fast and accurate waveform models are fundamentally important to modern gravitational wave astrophysics, enabling the study of merging compact objects like black holes and neutron stars. However, generating high-fidelity gravitational waveforms through numerical relativity simulations is computationally intensive, often requiring days to months of computation time on supercomputers. Surrogate…