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Institute of Astronomy



I am interested in astrophysical searches of light Axion-Like Particles (ALPs) and in understanding the growth and evolution of Supermassive Black Holes (SMBHs). I am currently developing a simple phenomenological model to describe the underlying population of SMBH spins from the observational estimates inferred by relativistic X-ray reflection studies. I have recently worked on the projected sensitivity of next-generation X-ray missions (in particular, the Athena and the proposed AXIS, LEM andSTROBE-X observatories) to constraining light ALPs. I am a working group member of STROBE-X

My broad research interests include: galaxy clusters, accretion, and astrophysical magnetic fields. 

Please refer to my personal website for more information.


Selected papers

First-authored journal publications

Current and Future constraints on Very-Light Axion-Like Particles from X-ray observations of cluster-hosted Active Galaxies (to appear at Memorie della SAIt in December 2023 for the Proceedings of the European Astronomical Society 2022 Annual Meeting Symposium S3) - J. Sisk-Reynés, Christopher S. Reynolds, James H. Matthews (2023)

Physics Beyond the Standard Model with Future X-ray Observatories: Projected Constraints on Very-Light Axion-Like Particles with Athena and AXIS - J. Sisk-Reynés, Christopher S. Reynolds, Michael L. Parker, et al. (2023, ApJ, 915, 5)

Evidence for a moderate spin from X-ray reflection of the high-mass supermassive black hole at the centre of the cluster-hosted quasar H1821+643 - J. Sisk-Reynés, Christopher S. Reynolds, James H. Matthews, et al. (2022, MNRAS, 514, 2)

New constraints on light Axion-Like Particles using Chandra Transmission Grating Spectroscopy of the powerful cluster-hosted quasar H1821+643 - J. Sisk-Reynés, James H. Matthews, Christopher S. Reynolds, et al. (2021, MNRAS, 510, 1)

Co-authored journal publications

How do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-ray Case Study with NGC 1275 - James H. Matthews, Christopher S. Reynolds, M.C. David Marsh, J. Sisk-Reynés, Payton E. Rodman (2022, ApJ, 930, 1)


2020 - 2022. University of Cambridge - Undergraduate Supervisions: Astrophysical Fluid Dynamics (Part II, 3rd year) and Mathematics 1A (Natural Sciences, 1st year).

2019. University of Manchester - Particle physics summer research: On direct dark matter detection at the DarkSide-20k liquid Argon experiment (mentors: Prof. Darren Price and Dr. Andrej Szelc).

2018 - 2019: Teaching placements in the UK: Teach First Insight Programme (2019), Teach Physics Internship from the Ogden Trust (2018).


2020 - present: Ph.D. in Astronomy, Institute of Astronomy (IoA), The University of Cambridge (primary supervisor: Prof. Chris Reynolds).

2016 - 2020: MPhys (Hons) Physics, The University of Manchester. Integrated Bachelor's + Master's degree in Physics.

Awards and Prizes

2023 - Fluid Dynamics for Astrophysics Summer School: Sponsored attendance on two-week programme at the Center for Computational Astrophysics, Flatiron Institute, Simons Foundation, New York.

2022 - Paul Murdin Prize (Institute of Astronomy): for the best paper produced by a current Ph.D. student for MNRAS 510, 1, pages 1264 - 1277. Shared.

2020 - Stellify Award (University of Manchester): for contributions and commitment as an undergraduate student in the areas of volunteering, leadership and ethical grand challenges.

Press Releases

May 2023 - Physics Beyond the Standard Model with Future X-ray Observatories

June 2022 - Chandra Shows Giant Black Hole Spins Slower Than Its Peers 

Talks and Scientific Conferences

Upcoming talks and events

(TBC) Invited AGN Seminar, NASA Goddard Space Flight Center (Greenbelt, Maryland).  

Delivered talks about my research at 20 scientific conferences (national and international level) and specialised group meetings since spring 2022. Invited and contributed presentations include short (15 minutes) and long (60 minutes) overviews.

Invited talks at: KIPAC Tea Talk series for KIPAC (Stanford University) and SLAC members (virtual); NewAthena UK Community Science Meeting (Edinburgh, UK); cosmology subgroup meeting of the STROBE-XCollaboration (virtual); AXIS mission monthly Seminar (virtual); High Energy Special Seminar at the Center for Astrophysics | Harvard & Smithsonian (Cambridge, Massachusetts); Chandra/HETG Special Seminar at MIT Kavli Institute (Cambridge, Massachusetts); Line Emission Mapper(LEM) IGM Working Group meeting (virtual); Fermi Group at NASA Goddard Space Flight Center (Greenbelt, Maryland).

Contributed talks at the following conferences: NAM 2023 - Parallel Session on "The future of X-ray astronomy in the UK" (Cardiff, UK); "The X-ray Universe" Conference (two talks; Athens, Greece); Royal Astronomical Society Specialist Discussion Meeting on "Evidence for SMBH Binaries" (London, UK); 3rd Scientific Conference dedicated to the Athena X-ray Observatory (Barcelona, Spain); "Progress in Axion Theory and Experiment Workshop" (Durham, UK); the European Astronomical Society Annual Conference (Valencia, Spain); the XMM-Newton "Black Holes under the X-ray microscope" Workshop (ESAC, Madrid, Spain); "New Results in X-ray Astronomy Annual UK meeting" (Edinburgh and Leicester, UK).

Diversity and Inclusion and Science Outreach 

Upcoming events 

(8th March 2024) Invited talk on "Supermassive Black Holes" for the Lindemann Science Day in Magdalene College, Cambridge. Anticipated attendance: 160 schoolchildren. 

Highlighted events 

Talks about "Black Holes: Extreme Objects in the Universe" to a total of 160 Year 6 students for an "Communicating Science" event organised by the Lindemann Trust (10th March 2023; Cambridge, UK).

"International Women's Day" at the IoA, where I was actively involved in organising some of the activities planned for the day, including a discussion panel with Physics and Astronomy professionals holding positions in academia and in industry (8th March 2022 and 7th-8th of March 2023). 

Organiser of Newnham College's Middle Common Room Seminar Speaker Series from December 2022 to November 2023. Curated a four-lecture series on the Legacies of Slavery and Reparative Justice in different environments (see event featuring Prof Catherine Hall).

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