Here is an animation of one of my hydrodynamic simulations of photoevaporative disc winds. The animation shows the fiducial simulation, from Alexander, Clarke & Pringle (2006a) (see publications page). This simulation models the late evolution of a disc around a 1 solar-mass star, with aspect ratio H/R=0.05 and an ionizing flux of 10^41 photon/s, on a 400x200 cell grid. The ionized material has sufficient thermal energy to be unbound, and flows away from the disc surface as a photoevaporative wind. The animation shows the evolution of the disc over the first 500yr of the simulation, which corresponds to approximately 18.5 outer orbital periods. Aside from some initial transients (due primarily to the use of a numerical density floor in the initial conditions), the wind is very stable over the duration of the simulation. The animation plots the density of the disc as a colour scale, with the ionization front shown as a dashed line. Velocity vectors are plotted at regular intervals, but are omitted if they are very small or if the density at that point is below the minumum of the colour scale.

This animation shows the evolution of dust and gas during the clearing phase of protoplanetary disc evolution. The animation shows the high-viscosity (alpha=0.01) simulation from Alexander & Armitage (2007) (see publications page). The animation shows the differential motions of grains of different sizes due to turbulent diffusion and aerodynamic drag, calculated against the background of a gas disc that evolves subject to viscous diffusion and photoevaporative mass-loss. Further details of the calculations can be found in Alexander & Armitage (2007).

This animation shows the fragmentation of an eccentric accretion disc due to gravitational instabilties. The animation shows the results of the high-resolution simulation from Alexander et al. (2008) (see publications page). Surface density is shown on the colour scale, and the time is given in units of the orbital period at the inner disc boundary. The simulation was conducted using the Smoothed-Particle Hydrodynamics (SPH) code Gadget-2: this particular simulation used 5 million SPH particles to model the gas disc. The animation was rendered using SPLASH, created by Dan Price; further details of the calculations can be found in Alexander et al. (2008).

The beautiful image that adorns my homepage was also created from one of the simulations in this paper, although it was rendered purely for "artistic" purposes. It shows the column density in the fragmenting disc in one of the low-resolution runs with e=0.5, viewed from 15 degrees above the plane of the disc. A similar image, rendered from the same simulation, appears in this Science perspective by Phil Armitage.

These two animations show the effects of the cooling rate on the fragmentation of a self-gravitating accretion disc. The animations show the results of the two high-resolution simulations from Alexander, Armitage & Cuadra (2008) (see publications page) - the parameter τ determines the rate of cooling (low values result in faster cooling). The movies show the formation and fragmentation of a filament, and are plotted in a frame that is co-rotating with the disc at r=2. (Consequently, the disc shear flow moves upwards for r<2 and downwards for r>2.) Once again the simulations were conducted using Gadget-2, this time using 12.8 million SPH particles to model the gas disc, and the animations were again rendered using SPLASH. Further details of the calculations can be found in Alexander, Armitage & Cuadra (2008).

This animation shows one of the results of our population synthesis modelling of planet migration in evolving gas discs, from Alexander & Armitage (2009) (see my publications page). The animation shows how the accretion rates evolve in a series of individual models with randomly-sampled initial conditions, and how we use large numbers of such models to build up a probability distribution for the population. Giant planets form randomly in a subset of 10% of the models and then migrate inwards, and the effect of the planets on the accretion rate is clearly visible. This particular animation shows the results of the SCALE model set, which provided the best fit to the observed data; further details of the calculationss can be found in Alexander & Armitage (2009).