Protoplanetary discs and planet formation

Planets form in cold discs of dust and gas around young stars like the sun. We know, however, that only a small fraction of the material in these protoplanetary discs ends up in planets; most of the disc is either accreted on to the star or blown away in winds or jets. The figure to the right shows a numerical simulation of disc clearing by photoevaporation.

Much of my current research looks at how protoplanetary disc physics shapes the formation of planetary systems. I have built detailed numerical models of how these systems evolve, and used high-performance computing facilities to run large numbers of models in order to make statistical predictions for the properties of both protoplanetary discs and exoplanets. With PhD student Alex Dunhill, I looked at how disc-planet interactions alter planetary orbits, particularly the planets' eccentricity. With PhD student Tom Hands, I am studying the formation and dynamics of compact multi-planet systems. Recently I have also begun to model the evolution of discs around binary stars, with the aim of understanding the formation and evolution of circumbinary planets such as Kepler-16b. Detailed discussion of these issues can be found in our recent review chapter in Protostars & Planets VI.

Super-massive black holes

My other main topic of research is the formation and evolution of super-massive black holes (SMBHs) at the centres of galaxies. These cosmic giants are millions to billions of times more massive than the sun, and play a key role in shaping the formation and evolution of galaxies.

A key question in the evolution of SMBHs is how they accrete gas. Much of my research in this area has focused on Sgr A*, the SMBH at the centre of the Milky Way. I showed how the gas disc around Sgr A* broke up into stars (shown in the simulation to the left), and looked in detail at how those stars grew and interacted. With SURE summer student Sarah Smedley, I investigated the fate of the gas left over when the disc around Sgr A* formed stars. I've also addressed the long-standing puzzle of how pairs of SMBHs are driven together following the merger of two massive galaxies. With PhD student Alex Dunhill and former Leicester student Chris Nixon, I have recently shown that misaligned or retrograde accretion discs offer an elegant solution to this so-called "last parsec problem".

To read more about specific projects, please go to my publications page.