arXiv subjects

Eric W. Hirschmann

Publications and source records attributed to Eric W. Hirschmann.

At least 19 recordsLinked to original sources

arXiv2026

Dendro-GR at high mass ratios with high spins

The Laser Interferometer Space Antenna (LISA) launches in less than a decade; it will detect spinning high-mass-ratio binary black hole inspirals annually, alongside other third-generation gravitational wave detectors. High-mass-ratio systems occupy a regime where numerical-relativity simulations remain computationally expensive and technically demanding, especially with high spins at precessing orientations. This portion of parameter space thus remains undersampled, leading to significant bias in parameter estimation. We must close these gaps. Here we report key progress in Dendro-GR toward reducing the computational cost of high-mass-ratio binaries with spin. We evolve the first Dendro-GR binaries at mass ratio $q=24$ (nonspinning) and at $q=12$ with spins up to $\chi=0.8$ on both black holes, spanning various configurations. These proof-of-concept runs show strong evidence that Dendro-GR can simulate in this regime and beyond. The simulations generate accurate gravitational waveforms through multipole modes up to $\ell=8$, remain stable, keep constraint violations low and largely constant, conserve horizon mass, and have high computational efficiency with relatively low wall-hour cost. These results establish our starting line for systematic exploration of the high-mass-ratio, high-spin binary black hole systems that are needed for gravitational wave analysis.

gr-qc↗

arXiv2026

Nonlinear Stability of Kerr-Sen Black Holes in Merging Binaries

We investigate the stability of Kerr-Sen black holes, which arise in Einstein-Maxwell-dilaton-axion theory. Within a numerical relativity framework, we perform head-on binary black hole simulations with approximate initial data across a portion of the parameter space. We find that for nontrivial electric charge, a dilaton field persists through merger and that in the presence of spin, the remnant will also retain an axion field. The persistence of these fields for long times after merger strongly suggests the stability of these black holes within this alternative gravity theory. We further test whether initially unscalarized black holes will acquire hair in the presence of a scalar background. We find that black holes immersed in such a background retain scalar hair. Furthermore, we find that even initially unscalarized Kerr-Newman black holes will scalarize and remain scalarized throughout the evolution.

gr-qc↗

arXiv2025

Nyquist-resolving gravitational waves via orbital frequency-based refinement

Adaptive mesh refinement efficiently facilitates the computation of gravitational waveforms in numerical relativity. However, determining precisely when, where, and to what extent to refine when solving the Einstein equations poses challenges; several ad hoc refinement criteria have been explored in the literature. This work introduces an optimized resolution baseline derived in situ from the inspiral trajectory (ORBIT). This method uses the binary's orbital frequency as a proxy for anticipated gravitational waves to dynamically refine the grid, satisfying the Nyquist frequency requirements on grid resolution up to a specified spin weighted spherical harmonic order. ORBIT sustains propagation of gravitational waves while avoiding the more costly alternative of maintaining high resolution across an entire simulation, both spatially and temporally. We find that enabling ORBIT decreases waveform noise by an order of magnitude and better resolves high-order wave amplitudes through merger. Combined with WAMR and other improvements, updates to Dendro-GR decrease waveform noise, decrease constraint violations, and boost refinement efficiency each by factors of $\mathcal{O}(100)$, while reducing computational cost by a factor of four. ORBIT and other recent improvements to Dendro-GR begin to prepare us for gravitational wave science with next-generation detectors.

gr-qc↗

arXiv2022

Massively parallel simulations of binary black holes with Dendro-GR

We present results from the new Dendro-GR code. These include simulations of binary black hole mergers for mass ratios up to q=16. Dendro-GR uses Wavelet Adaptive Multi-Resolution (WAMR) to generate an unstructured grid adapted to the spacetime geometry together with an octree based data structure. We demonstrate good scaling, improved convergence properties and efficient use of computational resources. We validate the code with comparisons to LazEv.

gr-qc↗

arXiv2017

Black Hole Dynamics in Einstein-Maxwell-Dilaton Theory

We consider the properties and dynamics of black holes within a family of alternative theories of gravity, namely Einstein-Maxwell-dilaton (EMD) theory. We analyze the dynamical evolution of individual black holes as well as the merger of binary black hole systems. We do this for a wide range of parameter values for the family of EMD theories, investigating, in the process, the stability of these black holes. We examine radiative degrees of freedom, explore the impact of the scalar field on the dynamics of merger and compare with other scalar-tensor theories. We argue that the dilaton can largely be discounted in understanding merging binary systems and that the endstates essentially interpolate between charged and uncharged, rotating black holes. For the relatively small charge values considered here, we conclude that these black hole systems will be difficult to distinguish from their analogs within general relativity.

gr-qc↗

arXiv2015

Relativistic Hydrodynamics with Wavelets

Methods to solve the relativistic hydrodynamic equations are a key computational kernel in a large number of astrophysics simulations and are crucial to understanding the electromagnetic signals that originate from the merger of astrophysical compact objects. Because of the many physical length scales present when simulating such mergers, these methods must be highly adaptive and capable of automatically resolving numerous localized features and instabilities that emerge throughout the computational domain across many temporal scales. While this has been historically accomplished with adaptive mesh refinement (AMR) based methods, alternatives based on wavelet bases and the wavelet transformation have recently achieved significant success in adaptive representation for advanced engineering applications. This work presents a new method for the integration of the relativistic hydrodynamic equations using iterated interpolating wavelets and introduces a highly adaptive implementation for multidimensional simulation. The wavelet coefficients provide a direct measure of the local approximation error for the solution and place collocation points that naturally adapt to the fluid flow while providing good conservation of fluid quantities. The resulting implementation, OAHU, is applied to a series of demanding one- and two-dimensional problems which explore high Lorentz factor outflows and the formation of several instabilities, including the Kelvin-Helmholtz instability and the Rayleigh-Taylor instability.

astro-ph.IM↗

arXiv2011

Boosting jet power in black hole spacetimes

The extraction of rotational energy from a spinning black hole via the Blandford-Znajek mechanism has long been understood as an important component in models to explain energetic jets from compact astrophysical sources. Here we show more generally that the kinetic energy of the black hole, both rotational and translational, can be tapped, thereby producing even more luminous jets powered by the interaction of the black hole with its surrounding plasma. We study the resulting Poynting jet that arises from single boosted black holes and binary black hole systems. In the latter case, we find that increasing the orbital angular momenta of the system and/or the spins of the individual black holes results in an enhanced Poynting flux.

astro-ph.HE↗

arXiv2010

Chaotic orbits for spinning particles in Schwarzschild spacetime

We consider the orbits of particles with spin in the Schwarzschild spacetime. Using the Papapetrou-Dixon equations of motion for spinning particles, we solve for the orbits and focus on those that exhibit chaos using both Poincaré maps and Lyapunov exponents. In particular, we develop a method for comparing the Lyapunov exponents of chaotic orbits. We find chaotic orbits for smaller spin values than previously thought and with spins that could be realized astrophysically.

gr-qc↗

arXiv2009

Perturbed disks get shocked. Binary black hole merger effects on accretion disks

The merger process of a binary black hole system can have a strong impact on a circumbinary disk. In the present work we study the effect of both central mass reduction (due to the energy loss through gravitational waves) and a possible black hole recoil (due to asymmetric emission of gravitational radiation). For the mass reduction case and recoil directed along the disk's angular momentum, oscillations are induced in the disk which then modulate the internal energy and bremsstrahlung luminosities. On the other hand, when the recoil direction has a component orthogonal to the disk's angular momentum, the disk's dynamics are strongly impacted, giving rise to relativistic shocks. The shock heating leaves its signature in our proxies for radiation, the total internal energy and bremsstrahlung luminosity. Interestingly, for cases where the kick velocity is below the smallest orbital velocity in the disk (a likely scenario in real AGN), we observe a common, characteristic pattern in the internal energy of the disk. Variations in kick velocity simply provide a phase offset in the characteristic pattern implying that observations of such a signature could yield a measure of the kick velocity through electromagnetic signals alone.

astro-ph.HE↗

arXiv2008

Magnetized Neutron Star Mergers and Gravitational Wave Signals

We investigate the influence of magnetic fields upon the dynamics of and resulting gravitational waves from a binary neutron star merger in full general relativity coupled to ideal magnetohydrodynamics (MHD). We consider two merger scenarios, one where the stars begin with initially aligned poloidal magnetic fields and one with no magnetic field. Both mergers result in a strongly differentially rotating object. In comparison to the non-magnetized scenario, the aligned magnetic fields delay the final merger of the two stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal fields. These effects not only produce electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves.

gr-qc↗

arXiv2008

Simulating binary neutron stars: dynamics and gravitational waves

We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the \had computational infrastructure for distributed adaptive mesh refinement.

gr-qc↗

arXiv2007

Adaptive Mesh Refinement and Relativistic MHD

We solve the general relativistic magnetohydrodynamics equations using distributed parallel adaptive mesh refinement. We discuss strong scaling tests of the code, and present evolutions of Michel accretion and a TOV star.

gr-qc↗

arXiv2002

Critical behavior of gravitating sphalerons

We examine the gravitational collapse of sphaleron type configurations in Einstein--Yang--Mills--Higgs theory. Working in spherical symmetry, we investigate the critical behavior in this model. We provide evidence that for various initial configurations, there can be three different critical transitions between possible endstates with different critical solutions sitting on the threshold between these outcomes. In addition, we show that within the dispersive and black hole regimes, there are new possible endstates, namely a stable, regular sphaleron and a stable, hairy black hole.

gr-qc↗

arXiv2002

Collapse of a Scalar Field in 2+1 Gravity

We consider the problem of critical gravitational collapse of a scalar field in 2+1 dimensions with spherical (circular) symmetry. After surveying all the analytic, continuously self-similar solutions and considering their global structure, we examine their perturbations with the intent of understanding which are the critical solutions with a single unstable mode. The critical solution which we find is the one which agrees most closely with that found in numerical evolutions. However, the critical exponent which we find does not seem to agree with the numerical result.

gr-qc↗

arXiv2000

Critical Phenomena in Nonlinear Sigma Models

We consider solutions to the nonlinear sigma model (wave maps) with target space S^3 and base space 3+1 Minkowski space, and we find critical behavior separating singular solutions from nonsingular solutions. For families of solutions with localized spatial support a self-similar solution is found at the boundary. For other families, we find that a static solution appears to sit at the boundary. This behavior is compared to the black hole critical phenomena found by Choptuik.

math-ph↗

arXiv1999

New Critical Behavior in Einstein-Yang-Mills Collapse

We extend the investigation of the gravitational collapse of a spherically symmetric Yang-Mills field in Einstein gravity and show that, within the black hole regime, a new kind of critical behavior arises which separates black holes formed via Type I collapse from black holes formed through Type II collapse. Further, we provide evidence that these new attracting critical solutions are in fact the previously discovered colored black holes with a single unstable mode.

gr-qc↗

arXiv1998

Pair Production in the Collapse of a Hopf Texture

We consider the collapse of a global "Hopf" texture and examine the conjecture, disputed in the literature, that monopole-antimonopole pairs can be formed in the process. We show that such monopole-antimonopole pairs can indeed be nucleated in the course of texture collapse given appropriate initial conditions. The subsequent dynamics include the recombination and annihilation of the pair in a burst of outgoing scalar radiation.

hep-ph↗

arXiv1998

Spherical Self-Similar Solutions in Einstein-Multi-Scalar Gravity

We consider a general non-linear sigma model coupled to Einstein gravity and show that in spherical symmetry and for a simple realization of self-similarity, the spacetime can be completely determined. We also examine some more specific matter models and discuss their relation to critical collapse.

gr-qc↗