University of Hertfordshire
Astrophysics

Large galaxies, like our own Milky Way, commonly harbour supermassive black holes at their centres. These cosmic giants emit powerful radiation and jets while devouring surrounding gas. This black hole activity plays a pivotal role in galaxy evolution, serving as the primary force regulating the transformation of gas into stars in large galaxies and possibly influencing dwarf galaxies. However, accurately modelling black hole feedback poses a formidable challenge due to the vast range of spatial scales involved, from the black hole's accretion disc (around 10 light-days) to the cosmic web feeding gas to galaxies (around 1 billion light-years). Prior cosmological simulations have relied on ad-hoc 'subgrid' treatments of black hole feeding and feedback, significantly limiting their predictive capabilities. Recent observational breakthroughs have challenged these ad-hoc models, as the newly-launched James Webb Space Telescope has discovered more active black holes in the early Universe than predicted. This exposes a fundamental gap in our theoretical understanding of black hole activity. Moreover, radio telescopes around the world have detected a distinctive hum from supermassive black hole mergers, marking the first detection of gravitational waves in the supermassive regime. Existing simulations lack the complexity for self- consistent predictions for both electromagnetic and gravitational wave ('multi-messenger') tracers, necessitating more sophisticated galaxy formation models. As an 1851 Research Fellow, I will develop next-generation multi-scale models for supermassive black hole growth and feedback. Building on my pioneering work on black holes in dwarf galaxies and accretion disc physics, I will incorporate physical insights from small-scale general-relativistic magneto-hydrodynamical simulations of black holes into simulations of individual galaxies embedded within a realistic cosmological environment. I will then combine my multi-scale black hole evolution model with different black hole formation mechanisms, allowing me to constrain the origin of supermassive black holes. Finally, I will extend my model to large cosmological volumes, for the first time including all relevant scales from the accretion disc to the cosmic web in a single simulation, and make predictions for upcoming electromagnetic and gravitational-wave observatories. This work will be crucial to decipher the co-evolution of galaxies and supermassive black holes in the era of multi-messenger astronomy.