Dr James Matthews

Astrophysicist

About Me

I’m an astrophysicist working at the University of Oxford as a Royal Society URF. My research is at the intersection of theory and observation and my interests are fairly broad, but fundamentally I am interested in the extreme and exotic physics that can be probed using accreting black holes and the outflows they produce.

In particular, my work focuses on the origins of the highest energy cosmic rays, the physics of accretion disc winds, the disc-wind-jet connection in AGN and X-ray binaries, and the hydrodynamics of astrophysical jets on all scales. More recently, I have started using X-ray observations of cluster-hosted AGN to search for, and place limits on, axion-like particles, which are exotic dark matter candidates.

Some (fairly) recent highlights can be found below, together with a list of current projects, publications and talks. If you have any questions, please get in touch. You can also read my PhD thesis or CV.

Contact

james.matthews [at] physics [dot] ox [dot] ac [dot] uk

Oxford Astrophysics
The Denys Wilkinson Building, Keble Road, Oxford OX1 3RH

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A Few Highlights

SIROCCO code release

The public release of the Sirocco Monte Carlo radiative transfer and photoionization code, together with its documentation and the code release paper.

Chandra Shows Giant Black Hole Spins Slower Than Its Peers

A recent NASA press release from a paper led by Julia Sisk-Reynes, an IoA PhD student.

ALPRO code release

A new code I wrote to solve the axion-photon conversion problem, and an accompanying paper

A disc wind model for quasar emission line blueshifts

A 2023 paper, which uses SIROCCO to construct a disc wind model for quasar emission line blueshifts and accompanying data and code.

UV and Optical Disc Winds in X-ray Binaries

Two results from the past few years:

  • A UV wind detected in Swift J1858 by Noel Castro Segura et al. 2022: see Independent article and the Nature paper.
  • the unusual, variable disc wind in J1357.2: Royal Astrononomical Society, CNN or the University of Southampton.

    • UHECRs from Radio Galaxies

    Information and movies from a recent paper about UHECRs from shocks in the lobes of radio galaxies.

    Projects

    Modelling Black Hole Jets

    Astrophysical jets are observed in the radio and gamma-ray bands and are thought to be produced be powered by the accretion process and possibly the black hole spin. I use hydrodynamic simulations to model their propagation, particle acceleration and interaction with their environment, in both AGN and X-ray binary systems.

    Cosmic Ray Acceleration

    It is not yet understood where the highest energy cosmic rays originate. One of my main research goals is to figure out whether jets from AGN can accelerate the highest energy cosmic rays. More info here.

    Astrophysical searches for axions

    Axions and Axion-like particles are well-motivated extensions to the standard model, predicted by string theory, and important dark matter candidates. In the presence of external magnetic fields, axions and photons can interconvert, a property that can be used to search for axions with astrophysical observations. In particular, I am interested in novel techniques for modelling the axion-photon conversion process and using X-ray observations to search for evidence of axions. Currently, our group's work places the world-leading limits on axions with masses below 1e-11 eV or so.

    Disc Winds in Accreting Systems

    Disc Winds are ubiquitous in accreting systems. I spent my PhD developing a Monte Carlo radiative transfer and photoionization code, and used it to synthesize spectra of accreting objects with associated outflows. I continue to work on disc winds in AGN, X-ray binaries and accreting white dwarfs and I'm particularly fascinated by the physics and driving mechanisms of the outflows.

    Quasar and AGN unification and orientation

    It would be rather elegant if all accreting supermassive black holes could essentially be described by their mass, Eddington ratio and viewing angle. While countless other complications doubtless exist, I am very interested in testing this paradigm. Image credit: Shen & Ho 2014.

    Public Engagement

    My public engagement work has involved taking a huge inflatable planetarium into local schools, activities with the homeless in Oxford, the SETI Cipher Challenge and the #AstroAirport. I also enjoy giving public talks on alien life, axions, cosmic rays and black holes. You can check out my public YouTube talks for Astronomy on Tap and Cambridge Astronomy.

    Selected Publications

    Here are some of my favourite papers. You can find a full list of publications on ADS.

    SIROCCO: A Publicly Available Monte Carlo Ionization and Radiative Transfer Code for Astrophysical Outflows 2024
    Matthews, J. H., Long, K. S., Knigge, C., et al.,
    MNRAS, submitted, arXiv:2410.19908

    Getting More Out of Black Hole Superradiance: a Statistically Rigorous Approach to Ultralight Boson Constraints 2023
    Hoof, S, Marsh, D. J. E., Sisk-Reynes, j, Matthews, J. H., Reynolds, C.
    MNRAS, submitted, arXiv:2406.10337

    Studying the link between radio galaxies and AGN fuelling with relativistic hydrodynamic simulations of flickering jets 2023
    Whitehead, H. W., Matthews, J. H.
    MNRAS, 543, 2478

    How, where and when do cosmic rays reach ultrahigh energies? 2023
    Matthews, J. H., Taylor A. M.
    PoS(ECRS)010

    The origin of optical emission lines in the soft state of X-ray binary outbursts: the case of MAXI J1820+070 2023
    Koljonen, K., Long K. S., Matthews, J. H., Knigge, C.
    MNRAS, 521, 4190

    Testing AGN outflow and accretion models with C IV and He II emission line demographics in z ≈ 2 quasars 2023
    Temple, M. J., Matthews, J. H., Hewett, P. C. et al.
    MNRAS, 523, 646

    New constraints on light axion-like particles using Chandra transmission grating spectroscopy of the powerful cluster-hosted quasar H1821+643 2022
    Sisk-Reynes, J., Matthews, J. H., Reynolds, C. S., et al.
    MNRAS, 510, 1264

    A persistent ultraviolet outflow from an accreting neutron star binary transient 2022
    Castro Segura, N. et al. (including Matthews, J. H.)
    Nature, 603, 52

    Echoes of the past: ultra-high-energy cosmic rays accelerated by radio galaxies, scattered by starburst galaxies 2022
    Bell, A. R., Matthews, J. H.
    MNRAS, 511, 488

    Fourier formalism for relativistic axion-photon conversion with astrophysical applications 2022
    Marsh, M. C. D., Matthews, J. H., Reynolds C.~S., Carenza, P.
    Phys Rev D, 105, 6013

    How Do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-Ray Case Study with NGC 1275 2022
    Matthews, J. H., Reynolds C.S., Marsh M.C.D., Sisk-Reynes J., Rodman P. E.
    ApJ, 930, 90.

    Particle acceleration in radio galaxies with flickering jets: GeV electrons to ultrahigh energy cosmic rays 2021
    Matthews, J. H., Taylor, A. M.
    MNRAS, 503, 5948

    Placing LOFAR-detected quasars in C IV emission space: implications for winds, jets and star formation 2021
    Rankine, A. L.Matthews, J. H., Hewett, P. C., Banerji, M., Morabito L. K., Richards, G. T.
    MNRAS, 502, 4154

    Particle acceleration in astrophysical jets 2020
    Matthews, J. H., Bell, A. R.; Blundell, K. M..
    New AStronomy Reviews, 89, 101543

    Stratified disc wind models for the AGN broad-line region: ultraviolet, optical and X-ray properties 2020
    Matthews, J. H., Knigge, C., Higginbottom, N., Long, K. S., et al.,
    MNRAS, 492, 5540

    Hot, dense He II outflows during the 2017 outburst of the X-ray transient Swift J1357.2-0933 2019
    Charles, P., Matthews, J. H., Buckley, D., Gandhi P.; Kotze, E.; Paice, J.
    MNRAS Letters in press.

    Cosmic ray acceleration by shocks: spectral steepening due to turbulent magnetic field amplification 2019
    Bell, A., Matthews, J. H., Blundell, K.
    MNRAS, 488, 2466.

    Ultra-high energy cosmic rays from shocks in the lobes of radio galaxies 2019
    Matthews, J. H., Bell, A., Blundell, K., Araudo, A.,
    MNRAS, 482, 4303, arXiv:1810.12350

    Fornax A, Centaurus A other radio galaxies as sources of ultra-high energy cosmic rays 2018
    Matthews, J. H., Bell. A., Blundell, K., Araudo, A.,
    MNRAS Letters, 479, 76

    Radiation-hydrodynamic simulations of thermally driven disc winds in X-ray binaries 2017
    Higginbottom, N., Knigge, C., Long, K. S. Matthews, J. H., et al.,
    MNRAS, 479, 3651

    Cosmic Ray Acceleration by Relativistic Shocks: Limits and Estimates 2018
    Bell. A., Araudo, A., Matthews, J. H., Blundell, K.
    MNRAS, 473, 2364

    Quasar emission lines as probes of orientation: implications for disc wind geometries and unification 2017
    Matthews, J. H.; Knigge, C.; Long, K. S.
    MNRAS, 467, 2571

    The reverberation signatures of rotating disc winds in active galactic nuclei 2017
    Mangham, S. W., Knigge, C., Matthews, J. H.; Long, K. S.; Sim, S. A.; Higginbottom, N.,
    MNRAS, in press, DOI:10.1093/mnras/stx1863

    Testing Quasar Unification: Radiative Transfer in Clumpy Winds 2016
    Matthews, J. H.; Knigge, C.; Long, K. S.; Sim, S. A.; Higginbottom, N.. Mangham, S. W.
    MNRAS, 458, 293

    The impact of accretion disc winds on the optical spectra of cataclysmic variables 2015
    Matthews, J. H.; Knigge, C.; Long, K. S.; Sim, S. A.; Higginbottom, N.
    MNRAS, 450, 3.

    Line-driven Disk Winds in Active Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer 2014
    Higginbottom, N.; Proga, D.; Knigge, C.; Long, K. S.; Matthews, J. H.; Sim, S. A.
    The Astrophysical Journal, 789, 1.

    Selected Talks

    Invited Review: Sources of UHECRs July 2022
    European Cosmic Ray Symposium, Nijmegen

    Invited Review: Particle acceleration in AGN jets July 2022
    EuCAPT Symposium, Remote

    Jet Modelling in Radio-Loud AGN July 2022
    EAS 2020, Remote

    Invited Talk: Particle Acceleration in Jets July 2019
    A Centenary of Jets, Jodrell Bank

    Invited Review: Disc Winds in Accreting White Dwarfs July 2019
    From Winds to Jets, Amsterdam

    Invited Talk: UHECRs from Radio Galaxies December 2018
    Hillas Symposium, Heidelberg

    Invited Talk: UHECRs from Radio Galaxies November 2018
    Particle Acceleration Conference, Calabria

    Contributed Talk: UHECRs from Radio Galaxies November 2018
    UHECR 2018, Paris

    Invited Colloquia: UHECRs from Radio Galaxies 2017-2018
    Belfast, Manchester, Nottingham, Oxford, Southampton

    Testing Quasar Unification with Radiative Transfer Simulations June 2017
    AGN Winds on the Georgia Coast, Jekyll Island, GA

    Invited Review: Ultraviolet Astronomy March 2017
    Broadband Astrophysical Processes, Southampton

    Modelling the Spectra of Quasars: Clumpy Winds and Unification September 2015
    TORUS 2015, Winchester, UK

    Disc Winds Matter! Their impact on the optical spectra of cataclysmic variables September 2015
    The Golden Age of Cataclysmic Variables, Palermo, Italy

    Modelling the Spectra of Quasars: Clumpy Winds and X-ray Properties June 2015
    The Extremes of Black Hole Accretion, Madrid, Spain

    Modelling the Spectra of Quasars: Clumpy Winds and X-ray Properties June 2015
    Black Hole Accretion and AGN Feedback, Shanghai, China

    Public Talk- The Search For Alien Life 2015
    Stargazing Live on campus event, University of Southampton

    Modelling the Spectra of Quasars June 2014
    Accretion Disc Winds Meeting, Durham, UK

    The Impact of Disc winds on the optical spectra of Cataclysmic Variables 2012
    Cataclysmic Variables Meeting, Columbia University, New York

    Searching for Nearby Planets During Predicted Mesolensing Events 2012
    Exoplanet Lunch, Harvard CfA, USA

    Systematic Exoplanet Searches During Predicted Mesolensing Events [POSTER] 2012
    American Astronomical Society, AAS Meeting