Institute of Astronomy

- Julia Sisk-Reynes


Office: Obs O14
Office Tel: (01223) 337531
More Info (Internal)



I am interested in constraining very light Axion-Like Particles (ALPs) using the X-Ray transparency of galaxy clusters. I have worked in constraining very light ALPs using Chandra Transmission Grating spectroscopy of the powerful cluster-hosted quasar H1821+643. Using X-ray reflection methods, I have found evidence for a moderate spin of the high-mass Supermassive Black Hole at the centre of this quasar. I am currently focussing on testing the sensitivity of one of the next generation X-ray telescopes, the Athena X-Ray Observatory, expected to be launched in 2034, to constraining very light ALPs. 

Selected papers

First author 

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)


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)


2021 - 2022 First year Natural Sciences supervisions

Mathematics 1A [Emmanuel College]

2020 - 2021 Part II undergraduate supervisions 

Astrophysical Fluid Dynamics [Trinity College]

2019 - Summer research project in particle physics at the University of Manchester

Enlarging the energy recoil window for direct dark matter detection at the DarkSide-20k liquid Argon experiment.

Supervisors: Prof Darren Price and Dr Andrzej Szelc.

2019 - Teach First Insight Programme - London and Southampton, UK

2018 - Teach Physics Internship awarded by the Ogden Trust - Bury, UK


2020 - present: Ph.D. in Astronomy, Institute of Astronomy, The University of Cambridge

Supervisors: Prof Chris Reynolds and Dr Anastasia Fialkov. Collaborating with Dr James Matthews.

2016 - 2020: MPhys (Hons) Physics, The University of Manchester.

Awards and Prizes

2020 - Stellify Award 

Awarded by the University of Manchester in recognition of contributions and commitment made over the course of my undergraduate studies in the areas of volunteering, leadership and ethical grand challenges.

Page last updated: 20 April 2022 at 15:09