How compact object systems influence the microphysical, energetic, and dynamical properties of their surroundings.
Understanding how radiation (photons and particles, e.g., neutrinos) is produced in strong-gravity environments and subsequently attenuated by intervening media, thereby providing key information about the compact object, the state of the accreting material, and the underlying theory of gravity.
Calculating covariant and physically-accurate models of this radiation using a combination of phenomenology, theoretical physics, and computational astrophysics.
What I do
I authored and maintain the general-relativistic radiation transport (GRRT) code, “BHOSS”, which solves the equations of covariant polarised radiation transport and fully incorporates the effects of both special relativity and general relativity (or any metric theory of gravity).
By interfacing GRRT with general-relativistic magnetohydrodynamics (GRMHD) simulations, I calculate the multi-frequency polarised emissions from turbulent plasmas surrounding black holes.
These calculations enable constraints on black-hole mass and spin, accretion physics, and facilitate strong-field tests of gravity.
What I’m part of
Full member of the Event Horizon Telescope (EHT) collaboration since 2014. Since 2022: serving member of the EHT Science Council and co-chair the Gravitational Physics working group.
Full member of the European BlackHoleCam project since 2014.
An 8K movie I created of a supercomputer simulation of the black hole shadow from the supermassive black hole in our Galactic Centre (Sagittarius A*), as imaged at a wavelength of 1.3 mm (or 230 GHz frequency), which is the Event Horizon Telescope observing wavelength. Such long wavelengths are necessary to peer through most of the accretion disk material and resolve structure close to the event horizon. Movie calculated with my BHOSS general-relativistic radiation transport code coupled with time-dependent 3D simulation data from the general-relativistic magneto-hydrodynamics code BHAC. The set of model parameters I used is one of only a few which pass the observational data constraints (see EHTC Paper V, ApJ, 2022). For every second which passes in this movie, two minutes of real time have passed for Sagittarius A* (upper left timer). The inwardly moving swirling material is hot, turbulent plasma falling towards the event horizon of the black hole, which coincides with the dark region in the centre. The bright ring surrounding this dark region is the “photon ring”, which is a characteristic feature of black hole images where photons (i.e., electromagnetic radiation) emitted from the surrounding plasma are so strongly deflected by the black hole’s immense gravity that they orbit it multiple times before escaping and reaching our detectors. This movie was featured in several news outlets, including: BBC News (https://www.bbc.co.uk/news/science-en…), New Scientist (https://youtu.be/reZMBklA8-c and https://www.newscientist.com/article/…), The Telegraph (https://youtu.be/BPfzzJULIZc) and BBC Earth (https://youtu.be/PqkA_LEuzBo).Movie of the observed supermassive black hole shadow in Messier 87 (M87), as calculated in BHOSS and using magnetically arrested disk (MAD) a=0.9375 3D GRMHD data from BHAC. The observer inclination, flow orientation, jet position angle, 230 GHz compact flux density, and 43 GHz & 86 GHz jet widths all satisfy M87’s observational constraints. The bright ring in the centre is the result of gravitational lensing of photons which orbit the black hole. The dark central brightness depression is roughly coincident with the event horizon and the innermost clockwise-rotating material is predominantly counter-jet material. “Flickering” coincides with magnetic eruptions of plasma in the accretion disc, and tenuous wisps of material in the outer parts of each frame are visible when the magnetic field in the disc is closely aligned with the observer’s line of sight.
