About

James Stone is an Emeritus Professor of Astrophysical Sciences at Princeton University. His research program centers on the use of large-scale direct numerical simulations to study the gas dynamics of a wide range of astrophysical systems, from protostars to clusters of galaxies. He is one of the primary developers of the ZEUS code for astrophysical magnetohydrodynamics (MHD), and more recently, he and his collaborators have developed Athena, a high-order Godunov scheme for astrophysical MHD that utilizes adaptive mesh refinement (AMR). His work includes investigating hydrodynamic and MHD processes that lead to outward angular momentum transport in accretion disks, the production and propagation of highly supersonic, collimated jets from accretion disks around protostars and active galactic nuclei, and the properties of compressible MHD turbulence in cold molecular gas in the galaxy. Additionally, he studies the time-dependent evolution of strong shocks in the interstellar medium, the structure of radiatively driven winds and outflows from disks around hot stars and active galactic nuclei, and the effects of mergers and AGN feedback on hot X-ray emitting gas in galaxy clusters. James Stone is deeply involved in PICSciE, which provides access to high-performance computing systems and training in scientific computation and numerical analysis, and holds a joint appointment in the Program in Applied and Computation Mathematics (PACM).

Research topics

• Physics
• Astrophysics
• Mechanics
• Astronomy
• Computational physics

Selected publications

• Mass Transport, Turbulent Mixing, and Inflow in Black Hole Accretion

  ArXiv.org · 2025-09-17

  preprintOpen accessSenior author

  We investigate mass transport, mixing, and disk evolution in non-radiative black hole accretion flows using Lagrangian tracer particles embedded in general relativistic magnetohydrodynamics simulations. Our simulation suite spans magnetically arrested disk (MAD) and standard and normal evolution (SANE) states across a range of black hole spins. By tracking tracer trajectories, we directly measure both advective inflow and stochastic spreading of fluid elements. The tracer distributions are well described by a combination of coherent inward drift and Gaussian-like broadening, consistent with an advection-diffusion picture. MADs exhibit systematically faster inflow than SANEs, with retrograde flows showing the most rapid infall; the innermost stable circular orbit leaves little imprint in MADs but remains more visible in SANEs. Turbulent fluctuations drive strong radial dispersion in all cases, with a superdiffusive scaling of sigma ~ t^0.95 in MADs and sigma ~ t^0.75 in SANEs for high-spin prograde disks. Mixing times decrease toward the event horizon and are consistently shorter in MADs and retrograde configurations. Tracers also reveal how accretion sources shift over time: turbulence draws inflow from a broad range of initial radii, with rapid torus depletion in MADs driving the mean source radius outward as r ~ t^(2/3), while SANEs evolve more gradually with r ~ t^(1/2). We show that the finite mass of the initial torus has a strong influence on late-time behavior, especially in MADs, where imprints of differently sized initial conditions may be accessible as early as t ~ 10000 GM/c^3.

  PublisherOA PDFDOI

• The plunging region of a thin accretion disc around a Schwarzschild black hole

  Monthly Notices of the Royal Astronomical Society · 2025-07-30 · 4 citations

  articleOpen access

  ABSTRACT A set of analytic solutions for the plunging region thermodynamics has been developed recently under the assumption that the fluid undergoes a gravity-dominated geodesic plunge into the black hole. We test this model against a dedicated 3D global general relativistic magnetohydrodynamics simulation of a thin accretion disc around a Schwarzschild black hole using the code athenak . Provided that we include the effects of non-adiabatic heating (plausibly from grid-scale magnetic dissipation), we find excellent agreement between the analytic model and the simulated quantities. These results are particularly important for existing and future electromagnetic black hole spin measurements, many of which do not include the plunging fluid in their emission modelling. This exclusion typically stems from the assumption of a zero-stress boundary condition at the innermost stable circular orbit (ISCO), forcing all thermodynamic quantities to vanish. Instead, we find a non-zero $\delta _\mathcal {J}\approx 5.3 {{\, \rm per\, cent}}$ drop in the angular momentum over the plunging region, which is consistent with both prior simulations and observations. We demonstrate that this stress is small enough for the dynamics of the fluid in the plunging region to be well-described by geodesic trajectories, yet large enough to cause measurable dissipation near to the ISCO – keeping thermodynamic quantities from vanishing. In the plunging region, constant $\alpha$-disc models are a physically inappropriate framework.

  PublisherOA PDFDOI

• The Interplay of Parametric and Magnetorotational Instabilities in Oscillatory Shear Flows

  The Astrophysical Journal · 2025-09-10 · 1 citations

  articleOpen accessSenior author

  Abstract The evolution of warped disks is governed by internal, oscillatory shear flows driven by their distorted geometry. However, these flows are known to be vigorously unstable to hydrodynamic parametric instability. In many warped systems, this might coexist and compete with the magnetorotational instability (MRI). The interplay of these phenomena and their combined impact on the internal flows has not been studied. To this end, we perform three-dimensional, magnetohydrodynamic unstratified shearing box simulations with an oscillatory radial forcing function to mimic the effects of a warped disk. In the hydrodynamic study, we find that the parametric instability manifests as strong, vertical “elevator” flows that resist the sloshing motion. Above a critical forcing amplitude, these also emerge in our magnetized runs and dominate the vertical stress, although they are partially weakened by the MRI, and hence the system equilibrates with larger radial sloshing flows. Below this critical forcing, the MRI effectively quenches the parametric instability. In all cases, we find that the internal stresses are anisotropic in character and better described by a viscoelastic relationship with the shearing flows. Unfortunately, these important effects are typically unresolved in global simulations of warped disks and are simplified in analytically tractable models. The incorporation of such complex, warp-amplitude-dependent, viscoelastic stresses will sensitively regulate the laminar flow response and inevitably modify the detailed spatio-temporal evolution of warped systems.

  PublisherOA PDFDOI

• Performance-portable Binary Neutron Star Mergers with AthenaK

  The Astrophysical Journal Supplement Series · 2025-01-14 · 13 citations

  articleOpen access

  Abstract We introduce an extension to the AthenaK code for general-relativistic magnetohydrodynamics (GRMHD) in dynamical spacetimes using a 3+1 conservative Eulerian formulation. Like the fixed-spacetime GRMHD solver, we use standard finite-volume methods to evolve the fluid and a constrained-transport scheme to preserve the divergence-free constraint for the magnetic field. We also utilize a first-order flux correction (FOFC) scheme to reduce the need for an artificial atmosphere and optionally enforce a maximum principle to improve robustness. We demonstrate the accuracy of AthenaK using a set of standard tests in flat and curved spacetimes. Using a SANE accretion disk around a Kerr black hole, we compare the new solver to the existing solver for stationary spacetimes using the so-called “HARM-like” formulation. We find that both formulations converge to similar results. We also include the first published binary neutron star (BNS) mergers performed on graphical processing units (GPUs). Thanks to the FOFC scheme, our BNS mergers maintain a relative error of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">O</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> or better in baryon mass conservation up to collapse. Finally, we perform scaling tests of AthenaK on OLCF Frontier, where we show excellent weak scaling of ≥80% efficiency up to 32,768 GPUs and 74% up to 65,536 GPUs for a GRMHD problem in dynamical spacetimes with six levels of mesh refinement. AthenaK achieves an order-of-magnitude speedup using GPUs compared to CPUs, demonstrating that it is suitable for performing numerical relativity problems on modern exascale resources.

  PublisherDOI

• Performance-portable Numerical Relativity with AthenaK

  The Astrophysical Journal Supplement Series · 2025-06-01 · 6 citations

  articleOpen accessCorresponding

  Abstract We present the numerical relativity module within AthenaK , an open-source performance-portable astrophysics code designed for exascale computing applications. This module employs the Z4c formulation to solve the Einstein equations. We demonstrate its accuracy through a series of standard numerical relativity tests, including convergence of the gravitational waveform from binary black hole coalescence. Furthermore, we conduct scaling tests on OLCF Frontier, NERSC Perlmutter, and ALCF Aurora, where AthenaK exhibits excellent weak-scaling efficiency of 80% on up to 65,536 AMD MI250X GPUs on Frontier (relative to four GPUs) and 67% on Aurora up to 24,576 Intel Data Center Max Series GPUs (relative to 12 GPUs) and strong-scaling efficiencies of 84% and 77% on AMD MI250X and NVIDIA A100 GPUs on Frontier and Perlmutter, respectively. Additionally, we observe a significant performance boost, with 2 orders of magnitude speedup (≳200×) on a GPU compared to a single CPU core, affirming that AthenaK is well suited for exascale computing, and thereby expanding the potential for breakthroughs in numerical relativity research.

  PublisherDOI

• Cyclic Zoom: Multiscale GRMHD Modeling of Black Hole Accretion and Feedback

  ArXiv.org · 2025-04-23

  preprintOpen access

  We present a ``cyclic zoom'' method to capture the dynamics of accretion flows onto black holes across a vast range of spatial and temporal scales in general relativistic magnetohydrodynamic (GRMHD) simulations. In this method, we cyclically zoom out (derefine) and zoom in (refine) the simulation domain while using a central mask region containing a careful treatment of the coarsened fluid variables to preserve the small-scale physics, in particular the magnetic field dynamics. The method can accelerate GRMHD simulations by $\gtrsim 10^5$ times for problems with large-scale separation. We demonstrate the validity of the technique using a series of tests, including spherically symmetric Bondi accretion, the Blandford-Znajek monopole, magnetized turbulent Bondi accretion, accretion of a magnetized rotating torus, and the long-term evolution of an accreting torus about both Schwarzschild and Kerr black holes. As applications, we simulate Bondi and rotating torus accretion onto black holes from galactic scales, covering an extremely large dynamic range. In Bondi accretion, the accretion rate is suppressed relative to the Bondi rate by $\sim(10r_\mathrm{g}/r_\mathrm{B})^{1/2}$ with a feedback power of $\sim 0.01 \dot{M} c^2$ for vanishing spin, and $\sim 0.1 \dot{M} c^2$ for spin $a\approx0.9$. In the long-term evolution of a rotating torus, the accretion rate decreases with time as $\dot{M}\propto t^{-2}$ on timescales much longer than the viscous timescale, demonstrating that our method can capture not only quasi-steady problems but also secular evolution. Our new method likewise holds significant promise for applications to many other problems that need to cover vast spatial and temporal scales.

  PublisherOA PDFDOI

• Idealized Global Models of Accretion Disks with Strong Toroidal Magnetic Fields

  ArXiv.org · 2025-05-19

  preprintOpen accessSenior author

  We present global magnetohydrodynamic (MHD) simulations of accretion disks with a strong toroidal magnetic field using an equation of state that fixes the gas thermal scale height. The disk forms from the inflow of a rotating magnetized gas cloud with a toroidal magnetic field. We find that the system maintains a moderately strong mean azimuthal field in the midplane, with plasma-$β\sim1$, trans-Alfvénic fluctuations, and large accretion stresses $α\sim0.1$. The azimuthal field in the disk is continuously escaping along the vertical direction but is also replenished via a local dynamo. The inflowing gas initially forms a strongly magnetized Keplerian disk with $β\ll1$ and $α\gg 1$. The disk gradually collapses from the inside out over $\sim 50-80$ orbits to form a moderately magnetized disk with $β\sim1$ and $α\sim0.1$. Radial advection of azimuthal magnetic field can maintain $β\lesssim1$ exterior to the circularization radius but not inside of it. Inclusion of a net initial vertical magnetic field can lead to an even more strongly magnetized disk midplane, consistent with previous work. When the gas thermal scale is not resolved ($\lesssim 4$ cells per thermal scale height), however, the disk remains highly magnetized with $β\ll 1 $. We discuss our results in the context of related shearing box simulations and other global disk simulations. The level of angular momentum transport found here is consistent with that inferred observationally in dwarf novae and X-ray transient outbursts, unlike simulations of weakly magnetized accretion disks.

  PublisherOA PDFDOI

• Cyclic Zoom: Multiscale GRMHD Modeling of Black Hole Accretion and Feedback

  The Astrophysical Journal · 2025-07-08 · 12 citations

  articleOpen accessCorresponding

  Abstract We present a “cyclic zoom” method to capture the dynamics of accretion flows onto black holes across a vast range of spatial and temporal scales in general relativistic magnetohydrodynamic (GRMHD) simulations. In this method, we cyclically zoom out (derefine) and zoom in (refine) the simulation domain while using a central mask region containing a careful treatment of the coarsened fluid variables to preserve the small-scale physics, in particular the magnetic field dynamics. The method can accelerate GRMHD simulations by ≳10 5 times for problems with large-scale separation. We demonstrate the validity of the technique using a series of tests, including spherically symmetric Bondi accretion, the Blandford–Znajek monopole, magnetized turbulent Bondi accretion, accretion of a magnetized rotating torus, and the long-term evolution of an accreting torus about both Schwarzschild and Kerr black holes. As applications, we simulate Bondi and rotating torus accretion onto black holes from galactic scales, covering an extremely large dynamic range. In Bondi accretion, the accretion rate is suppressed relative to the Bondi rate by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>10</mml:mn> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">g</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> with a feedback power of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>0.01</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:msup> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> for vanishing spin and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>0.1</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:msup> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> for spin a ≈ 0.9. In the long-term evolution of a rotating torus, the accretion rate decreases with time as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> on timescales much longer than the viscous timescale, demonstrating that our method can capture not only quasi-steady problems but also secular evolution. Our new method likewise holds significant promise for applications to many other problems that need to cover vast spatial and temporal scales.

  PublisherDOI

• Tunable megawatt-scale sub-20  fs visible pulses from a fiber laser source

  Optica · 2025-04-28 · 5 citations

  articleOpen access

  Ultrafast laser pulses that are both tunable in wavelength and very short in duration are essential tools in fields ranging from biomedical imaging to ultrafast spectroscopy. While resonant dispersive-wave emission in gas-filled hollow-core fibers is a powerful technique for generating such pulses, it has traditionally required complex and expensive pump laser systems. In this work, we present a more compact and accessible alternative that combines gain-managed nonlinear amplification with resonant dispersive-wave emission. Our system produces sub-20 fs pulses tunable from 400 to beyond 700 nm, with energies up to 39 nJ and peak powers exceeding 2 MW, operating at a 4.8 MHz repetition rate. This compact and efficient laser source opens new avenues for deploying resonant dispersive-wave-based technologies for broader scientific and industrial applications.

  PublisherDOI

• Barriers to uptake of harm reduction techniques for GBMSM who use drugs in night-clubs and sex-on-premises venues in London and the Southeast: a mixed-methods, qualitative study

  Harm Reduction Journal · 2025-02-01 · 2 citations

  articleOpen accessSenior author

  BACKGROUND: Drug-related harm is a significant public health concern in the UK, particularly among underserved groups such as gay, bisexual, and other men who have sex with men (GBMSM). This study explores the role of night-time venues (for example night clubs or sex-on-premises venues) in promoting harm reduction strategies for GBMSM who use drugs, highlighting unique challenges within these spaces. METHODS: The study used a mixed-methods approach, including an online survey (n = 53) and semi-structured interviews (n = 8). Participants included GBMSM with lived experience of substance use in night-time venues, as well as those providing support to this population. Data was collected through a Likert-scale survey and thematic analysis of qualitative responses. RESULTS: Findings reveal dissatisfaction among survey respondents about the level of support for harm reduction provided by night-time venues, which are perceived as inconsistent in their approach towards substance use. The study also identifies economic and legal barriers faced by venues that prevent the endorsement of harm reduction techniques. CONCLUSIONS: Addressing these barriers could transform night-time venues into effective sites for harm reduction, particularly by targeting "afters" culture (the phenomenon where club-goers will return to a residential setting and continue substance use for prolonged periods 'after' the night-time venue closes or the event ends) and promoting safer practices. This research suggests that coordinated efforts with local government and policy reform are crucial to fostering safer environments for GBMSM.

  PublisherOA PDFDOI

Recent grants

• MHD Models of Accretion Disks in Close Binaries

  NSF · $312k · 2013–2017

• SAVI: A Max-Planck/Princeton Research Center for Plasma Physics

  NSF · $950k · 2012–2016

• A Max-Planck/Princeton Research Center for Plasma Physics

  NSF · $540k · 2015–2018

• MRI: Acquisition of a High-Performance Computing Cluster for Astrophysics

  NSF · $663k · 2007–2010

• Collaborative Research: Predicting the Observational Signatures of Accreting Black Holes

  NSF · $408k · 2017–2020

Frequent coauthors

• K. Werner

  54 shared

• I. Hubený

  42 shared

• Keith MacGregor

  42 shared

• Michael L. Norman

  University of California, San Diego

  41 shared

• Eve C. Ostriker

  31 shared

• Eliot Quataert

  26 shared

• Shane W. Davis

  University of Virginia

  24 shared

• Yan-Fei Jiang

  Flatiron Institute

  24 shared

Labs

• James StonePI