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 upper right shows a numerical simulation of disc clearing by photoevaporation. The main focus of my current research is using theoretical and computational models to understand how protoplanetary disc physics shapes the formation of planetary systems. Recent highlights include simulations of circumbinary planets such as Kepler-16b (as shown on lower right, in a numerical simulation by former PhD student Alex Dunhill), and PhD student Tom Hands' work on the formation and dynamics of compact multi-planet systems. Detailed discussion of these issues can be found in our recent review chapter in Protostars & Planets VI


From 2016-21 I am the Principal Investigator (PI) of Building planetary systems: linking architectures with formation (BuildingPlanS), a €1.95M project funded by the European Research Council (ERC). Understanding the extraordinary diversity of the "exoplanet zoo" has become one of the biggest challenges in modern astrophysics. The last decade has seen an explosion in our knowledge of planetary systems, but this dramatic increase in our knowledge has not been accompanied by a corresponding increase in our understanding: despite having discovered thousands of exoplanet systems, we still don't know how planets form, where planets form, or when planets form. BuildingPlanS aims to change this, by linking the observed architectures of exoplanet systems with their formation in protoplanetary discs. My team will build detailed computational models to understand the processes that shape the formation and evolution of planetary systems. We will then test this understanding against both new observations of planet-forming discs (with facilities such as ALMA and the VLT) and our ever-growing census of exoplanetary systems. The overall aim of BuildingPlanS is to link exoplanet architectures with their formation and establish a global picture of how planetary systems are built.

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.