My main research interest is in planet formation and I study the formation environment of planets, protoplanetary discs. I am best described as a theorist, and in particular as a computational astrophysicist; my main expertise is in numerical hydrodynamics (I am a developer of the hydrodynamical code GANDALF). However, the theory I prefer is the one that can be tested by observations, and I always like to stay as close as possible to observations (I do care about reality after all). Many of my collaborators are observers, I am involved in many observational studies (most notably two large programs on the ALMA telescope, exoALMA and AGE-PRO) and occasionally I even lead observations myself (e.g. ALMA observations of HD100453 and CI Tau).
DISC EVOLUTION AND DISPERSAL
Discs do not just sit there and then disappear after a few Myr (a timescale constrained by observations) but are constantly evolving. Because they provide the building blocks for forming planets, understanding disc evolution is a necessary step to understand planet formation. This is a topic I have always been interested in since my PhD (e.g. my 2013 and 2015 papers on the interplay between photo-evaporation and giant planets, or the possibility of reforming a disc by accreting the material in the vicinity of a star.).
Thanks to ALMA and other instruments, it is possible to do large disc surveys and so we now have a lot of data that we can compare to theoretical models of disc evolution. We are writing a review on this topic (led by my long term collaborator Carlo Manara) for the upcoming Protostars and Planets conference. The problem in particular I am most interested about is explaining why discs accrete, with the two main ideas being that the angular momentum in discs can be transported by processes called generically viscosity, or it can be removed through winds launched by the magnetic field (see Figure). Disc evolution proceeds very differently in the two cases. Luckily, it also means that it should be possible to use the observations to constrain which scenario is the most correct one – this would be great because this problem is very elusive and it is still open after decades of studies!
Most of the comparisons between models and the results of disc surveys have been done only for the viscous framework. See for example this paper of mine where I showed how the viscous scenario reproduces an observed correlation (see Figure) between mass accretion rates and disc masses, or this paper where together with Leon Trapman we looked at the evolution of the radii of the disc (there will be much more about the comparison in the PPVII review!).
More recently however I have also become interested in developing models of the alternative, wind models. We recently published a theoretical paper with Benoit Tabone where we found new analytical solutions to describe the evolution of discs under the influence of winds. We will get new data from the recently approved ALMA Large Programme AGE-PRO that will be perfect to compare these solutions with observations – a lot of work coming up!
SIGNATURES OF PLANETS IN DISCS
Thanks to new amazing telescope such as ALMA, SPHERE and GPI, we can now image discs in exquisite details, reaching resolutions up to 1 AU. At these high resolutions, if discs contain young, forming planets, we can see the effects of these planets on the disc. In this way, although we cannot see directly the planets, we can infer that they are present. Amazingly, when observed at high resolution, discs show a lot of structures (see Figure from the DSHARP survey) such as gaps, rings and spirals, that could very well be produced by young planets!
To interpret these images, we need models of discs-planet interaction, and this is where I play a role. I am an expert in running these hydro-dynamical simulations, which include both the dust and gas dynamics. I then use radiative transfer to generate simulated observations, which I compare with the real ones (see example in the Figure, from this paper). Until recently many of these simulations were run in 2D assuming that disc is flat, but to increase the realism we are now moving to 3D (e.g. this paper), which really require supercomputers to run.
A very recent development of the last 2-3 years is, in addition to the images, using the information contained in the very precise measurements of the gas velocity that ALMA can do using the Doppler effect. Some of these measurements present very clear signatures of the presence of a planet (see for example the Figure). To make it easier to look for such signatures, I am involved in the development of the DISCMINER analysis tool. I am also involved in the exoALMA Large Programme that will measure the gas velocity in 15 new discs – a lot of work to do in the future also on this side!
Besides the direct observational applications, I am also interested in disc-planet interaction in general, which is very important to understand planet formation. See for example this paper with Enrico Ragusa where we found that on very long timescales (hundreds of thousands of orbits) the disc can make the orbits of giant planets eccentric. Running these simulations took a lot of time – literally months on supercomputers!