arXiv subjects

Conor Dyson

Publications and source records attributed to Conor Dyson.

7 recordsLinked to original sources

arXiv2026

Dynamics of Relativistic Binaries in Structured and Stochastic Environments: A Lagrange-Fourier-Hansen Framework

We develop a general framework to characterize non-vacuum perturbations to relativistic binaries in the gravitational-wave (GW) driven regime, for use in GW parameter estimation studies. The effect of smooth, structured and stochastic perturbations to the binary's motion is reduced to a resonant spectral projection defined on a rolling averaging window, with weights given by Hansen coefficients. This is combined with practical criteria for identifying and evaluating the corresponding dynamical response to perturbations, starting from either analytical models or numerical simulations of binaries in environments. The result is a set of coupled ODEs for the orbital elements that capture epi-cyclic, apsidal and nodal resonances, consistently incorporate feedback from radiation reaction and can be solved efficiently on a coarse time grid. We demonstrate the practical application of the framework in two representative astrophysical scenarios: a compact binary in a variable tidal field and an extreme-mass-ratio inspiral in an accretion disk. We propose the Lagrange-Fourier-Hansen framework as a unified tool for modeling environmental effects in GW templates for eccentric and precessing binary sources, and particularly for bridging the gap between phenomenological prescriptions and realistic models of binaries in environments.

gr-qc↗

arXiv2026

Spiral Density Waves and Torque Balance in the Kerr Geometry

Extreme mass-ratio inspirals (EMRIs) in relativistic accretion discs are a key science target for the upcoming LISA mission. Existing models of disc-EMRI interactions typically rely on crude dynamical friction or Newtonian planetary migration prescriptions, which fail to capture the relativistic fluid response induced by the binary potential. In this work we address this gap by providing the relativistic calculation. We apply standard methods from self-force theory, black hole perturbation theory, and relativistic stellar perturbation theory to perform the full fluid calculation of the relativistic analogue of planetary migration for the first time. We calculate the response of a fluid in the perturbing potential of an EMRI consistently incorporating pressure effects. Using a master enthalpy-like variable and linearised fluid theory, we reconstruct the fluid perturbations and relativistic spiral arm structure for a range of spin values in the Kerr geometry. We conclude by deriving a relativistic torque-balance equation that enables computation and comparison of local torques with advected angular momentum through the disc. This opens a promising route towards establishing torque-balance relations between integrated disc torques arising from fluid perturbations and the forces acting on EMRIs embedded in matter.

gr-qc↗

arXiv2025

Lensing and wave optics in the strong field of a black hole

Gravitational waves (GWs) are lensed by matter, offering a unique probe of both the large-scale structure of the Universe and the fundamental properties of GW propagation. GWs can also be affected by wave optics effects when their wavelength is comparable to the size of the lens. While this regime has been well studied in the Newtonian approximation, the role of strong gravitational fields remains largely unexplored. This is particularly relevant for lensing by intermediate and supermassive black holes (BHs), which can occur near active galactic nuclei or in compact triple systems. In this work, we analyze the lensing of GWs by a non-rotating BH and compare our results to the Newtonian point-mass approximation. We construct frequency-dependent amplification factors that incorporate strong-field effects, revealing explicit polarization mixing and absorption by the event horizon. Using a fiducial GW event, we explore key phenomenological signatures of BH lensing, highlighting new observational opportunities to probe strong gravitational fields through GW lensing.

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arXiv2025

Environmental effects in extreme mass ratio inspirals: perturbations to the environment in Kerr

Future gravitational wave observatories open a unique avenue to study the environments surrounding black holes. Intermediate or extreme mass ratio inspirals will spend thousands to millions of cycles in the sensitivity range of detectors, allowing subtle environmental effects to accumulate in the gravitational waveform. Working in Lorenz gauge and considering equatorial circular orbits, we present the first self-consistent, fully relativistic calculation of a perturbation to a black hole environment due to an inspiraling secondary in the Kerr geometry. As an example case, we consider the environment to be that of a superradiantly grown scalar cloud, though our framework is generalizable to other scenarios. We demonstrate that the scalar field develops a rich wake structure induced by the secondary and compute scalar fluxes emitted to infinity and through the horizon. Relative differences in the fluxes compared to Schwarzschild are tens of percent on large intervals of parameter space, underscoring the importance of modeling in Kerr.

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arXiv2024

Relativistic aerodynamics of spinning black holes

Astrophysical black holes do not exist in vacuum, and their motion is affected by the galactic environment. As a black hole moves it attracts stars and matter, creating a wake that, in turn, exerts an effective friction slowing down the black hole. This force is known as dynamical friction, and has significant consequences, ranging from the formation of supermassive black hole binaries to modifications in the phase of binary mergers. In this work we explore the motion of spinning black holes on a medium. We find that the classical drag along the velocity direction is modified and two novel forces appear: a rotational force, which in the context of fluid dynamics is dubbed the Magnus force, and a lift, orthogonal to the direction of motion. We develop a first-principles fully-relativistic treatment of these spin-induced aerodynamic forces in two types of environment: i) collisionless corpuscular matter and ii) a light scalar field, exploring the differences between both cases. In both cases we find that the total rotational force acts precisely in the opposite direction as compared to the classical set-up of a spinning ball moving through a fluid. Finally, we comment on the consequences of these new effects for astrophysics and gravitational wave observations.

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arXiv2023

Magnetic Black Holes: from Thomson Dipoles to the Penrose Process and Cosmic Censorship

We consider accretion of charged test matter by rotating, magnetic black holes and discuss a number of aspects in which the interaction of the angular momentum contained in the electromagnetic field and the spin of the hole plays a fundamental role. First, we argue that such a black hole tends to lose its angular momentum by accreting charges while remaining globally neutral. Then, we show that accretion can happen in a superradiant manner via an enhanced Penrose process. In particular, we find that the regions from which energy and angular momentum can be extracted contain the axis of rotation and, in some cases, consist of floating bubbles disconnected from the black hole itself. Finally, we address the question of whether extremal dyonic rotating black holes can be overcharged or overspun via accretion of arbitrary matter, and prove that this can not happen if the null-energy condition holds. We conclude by discussing some future research directions.

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arXiv2023

Kerr-fully Diving into the Abyss: Analytic Solutions to Plunging Geodesics in Kerr

We present closed-form solutions for plunging geodesics in the extended Kerr spacetime using Boyer-Lindquist coordinates. Our solutions directly solve for the dynamics of generic timelike plunges, we also specialise to the case of test particles plunging from a precessing innermost stable circular orbit (ISSO). We find these solutions in the form of elementary and Jacobi elliptic functions parameterized by Mino time. In particular, we demonstrate that solutions for the ISSO case can be determined almost entirely in terms of elementary functions, depending only on the spin parameter of the black hole and the radius of the ISSO. This extends recent work on the case of equatorial plunges from the innermost stable circular orbit. Furthermore, we introduce a new equation that characterizes the radial inflow from the ISSO to the horizon, taking into account the inclination. For ease of application, our results have been implemented in the KerrGeodesics package in the Black Hole Perturbation Toolkit.

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