Debris disks are complex systems that involve interaction between a variety of physical processes: mutual collisions between particles in the disk that span sizes from micron-sized dust to 1000 km-sized dwarf planets, interaction with stellar radiation resulting in Poynting-Robertson drag and radiation pressure, gravitational perturbations from nearby planets or nearby stars, interaction with stellar winds, Lorentz forces, Yarkovsky forces, sublimation, gas drag, to name a few. Modelling of these interactions require a variety of analytical and numerical techniques. Comparison with observations of the structure of debris disks, and of how the level of dust emission varies with age (by comparing dust around stars of different ages), as well as other stellar parameters, provide vital tests of the models. One example of such numerical work is shown in the animation. The first panel is the disk luminosity of dust grains from an asteroid belt migrating past a Neptune mass planet, where some are caught in mean motion resonances.  The second panel is the flux transmitted through the Large Binocular Telescope Interferometer’s fringe pattern.  Measuring the transmitted flux over an orbit of the planet, the presence of structure can be inferred, and the properties of the planet inferred. For habitable zones around Sun-like stars, such as those probed by LBTI, the planet’s orbit will be approximately a year, making repeated measurements plausible.

A new side of debris disk theory is emerging thanks to many recent gas observations with the biggest spatial and ground-based telescopes (Herschel, HST, ALMA, ...). CO gas is observed around a handful of young systems (see observations) and seems collocated with the dust. This raises many questions as this gas should be rapidly destroyed by strong UV photons (photodissociation). This implies that CO is secondary gas (rather than primordial gas remnants) permanently replenished within the debris disk. Some atomic species such as neutral and ionised carbon or oxygen are also observed. Our team works on developing new state-of-the-art models that can explain all these observations at once. We aim to solve the conundrum of the origin of the gas, explain its evolution and study the coupling between this gas and the dust. Our first study was applied to the famous beta pic system where we can reconcile all the observations  and, for instance, predict the future C I observation by ALMA (see figure below from Kral+16).