EDGE is a project to model the very smallest stellar systems in the Universe – dwarf galaxies, globular star clusters and nuclear star clusters. We are interested in where these came from, how they behave, and crucially what observing them can teach us about fundamental physics and cosmology.
All galaxies – even big, impressive spirals like our Milky Way that are millions of times more massive than those we model – are built from these tiny (in relative terms!) building-blocks. However, it turns out the physics of how they form is incredibly sensitive to fundamental questions like where structure in our universe originated, how stars interact with their surrounding gas, and the nature of the mysterious dark matter which appears to dominate the Universe’s composition. We know that dark matter is some kind of extra mass in the universe, not directly visible, and these tiny cosmic structures are excellent laboratories in which to reveal its nature.
Tackling such problems requires intensive computational simulations. These simulations start from some basic assumptions about how the universe works – how much dark matter and normal matter there is, how gravity works, how stars light up and heat the gas, and so on. The computer uses these assumptions to track the cosmic history of how structures assemble over time. To track all this with the greatest possible physical fidelity requires state-of-the-art supercomputers, and the DiRAC system at Leicester has been tailored to solve problems of exactly this type.
Astha is a second-year PhD student in Astrophysics at the University of Surrey. Her research explores how dwarf galaxies evolve, using the EDGE simulations to study their mass-metallicity relationship. Astha has always been fascinated by how small galaxies can tell big stories about the universe. Outside of her research, she enjoys science communication, and loves unwinding with a game of badminton or a good singing session.
Ethan Taylor has been a part of the EDGE collaboration since starting his PhD in 2020. He is now a postdoctoral researcher at the University of Surrey, where he is studying the interplay between globular clusters and dwarf galaxies. Before his PhD, Ethan wasn’t entirely sure what he wanted to specialise in. However, he is very happy to have joined an amazing international collaboration filled with supportive people who have helped him build and grow in confidence as an independent researcher. Having grown up in a less privileged area of Nottingham, Ethan is passionate about giving back to the community that helped him get to where he is today. Outside of research, Ethan is always looking to support aspiring Black students and help make the field more diverse and inclusive for everyone. After all, “Out of many, one people.”
Our simulations have revealed three new types of galaxy that should be found in up-coming surveys, and showed how dark matter can be “heated up” and pushed out of the centres of even the very smallest dwarfs by star formation. For the first time we’ve produced models in which dense stellar systems – globular and nuclear star clusters – naturally emerge; and also predicted a new type of object with properties intermediate between star clusters and dwarf galaxies. If these new objects can be found observationally, they could be a natural “rosetta stone” both for understanding dark matter and hunting down the first “metal free” stars in the Universe.
For the future, now higher-fidelity models are available EDGE’s glimpse of galaxy formation via simulations will radically evolve. EDGE reaches a spatial resolution of just ~9 lightyears and ~100 solar masses for a large suite of dwarfs over a wide mass range, so that a remarkable level of realism emerges naturally, largely robust to choices of numerical model parameters. This marks a step-change in what can be done with simulations; for instance, incorporating black hole physics throws open the question of the origin of the super-massive black holes observed at the centres of galaxies, and also informs interpretations of future gravitational wave observations revealing the Universe at its earliest times. EDGE promises to herald a new era in which galaxy formation simulations transition from explaining existing data to making testable predictions.
EDGE: A new model for Nuclear Star Cluster formation in dwarf galaxies
Emily I. Gray, Justin I. Read, Ethan Taylor, Matthew D. A. Orkney, Martin P. Rey, Robert M. Yates, Stacy Y. Kim, Noelia E. D. Noël, Oscar Agertz, Eric Andersson, Andrew Pontzen
EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations
Martin P. Rey, Ethan Taylor, Emily I. Gray, Stacy Y. Kim, Eric P. Andersson, Andrew Pontzen, Oscar Agertz, Justin I. Read, Corentin Cadiou, Robert M. Yates, Matthew D. A. Orkney, Dirk Scholte, Amélie Saintonge, Joseph Breneman, Kristen B. W. McQuinn, Claudia Muni, Payel Das
