I work on the formation and structure of galaxies from a theoretical perspective. The present structure of a galaxy is intimately connected how the galaxy formed because galaxies are slow-moving beasts - it takes 200,000,000 years for the Sun to rotate once about the galactic centre. So galaxies evolve slowly. Moreover, unlike a cup of hot tea, a galaxy lacks an equilibrium state to which it can relax: it's doomed to move on for ever, never to arrive.
In recent years our focus has been on our own Galaxy, the Milky Way, because we can observe it in increasingly exquisite detail and a major goal of contemporary astronomy is to deduce the Galaxy's history from its present structure. Dynamical models play a key role in this process and my research group specialises in the construction of such models and fitting them to observational data.
This is a golden age of astronomical surveys, and we are struggling to exploit data currently taken by large ground-based telescopes and are bracing ourselves for data to flow from Gaia, a Cornerstone Mission of the European Space Agency, which will be launched in the second half of 2013. These data will revolutionise our knowledge of the Galaxy.
Four-fifths of the matter in the Universe is supposed to be contained in unknown dark-matter particles. Currently our only means of detecting this matter is by measuring its gravitational field. Our models are key for this endeavour.
The great majority of ordinary matter is not in galaxies but is thought to be contained in diffuse plasma that fills intergalactic space. With colleagues in Bologna I have been developing a model of how galaxies exchange material with this vast reservoir.
A related topic to which I have contributed is the impact on the intergalactic and interstellar media of the massive black holes that sit at the centres of galaxies. We were pioneers of the now generally accepted view that energy released as these objects accrete diffuse gas is responsible for keeping most interstellar gas too hot to form stars.
Over the years I have taught a wide range of topics in physics and mathematics. I've coauthored a 2-volume graduate text on galaxies, an introduction to the theory of critical phenomena, and an undergraduate text on quantum mechanics. (Three former Merton undergraduates were my coauthors on these last two books.) I believe physics should be defined as the mathematical description of phenomena, and that it is the core science. It is useful, but much more than that, it changes your understanding of what material reality is. I want nothing so much as to help others to understand the subject's power and range.