A planetary system as the origin of structure in Fomalhaut's dust belt

TLDR: The sharp inner edge and offset demonstrate the presence of planetary-mass objects orbiting Fomalhaut, demonstrating the structure of a dusty disk modified by the gravitational influence of planets.

Abstract: In 1983 the IRAS orbiting satellite detected excess infrared radiation from the direction of Fomalhaut, a first magnitude star in the otherwise dim constellation Piscis Austrinus. It was radiation from a huge dusty disk around the star, about four times the size of our Solar System. The Advanced Camera for Surveys onboard the Hubble Space Telescope has now detected Fomalhaut's dust complex at high resolution at optical wavelengths. The disk is offset from the star in a way that suggests the presence of several planets. The debris disks around Beta Pictoris and AU Microscopii are both edge-on, and the disk around HR 4796A has a small radius. So the Fomalhaut disk, seen on a slope rather like the ring around Saturn, older than the others and closer to us, may become the disk of choice for the study of planet formation. The Sun and >15 per cent of nearby stars are surrounded by dusty disks that must be collisionally replenished by asteroids and comets, as the dust would otherwise be depleted on timescales <107 years (ref. 1). Theoretical studies show that the structure of a dusty disk can be modified by the gravitational influence of planets2,3,4, but the observational evidence is incomplete, at least in part because maps of the thermal infrared emission from the disks have low linear resolution (35 au in the best case5). Optical images provide higher resolution, but the closest examples (AU Mic and β Pic) are edge-on6,7, preventing the direct measurement of the azimuthal and radial disk structure that is required for fitting theoretical models of planetary perturbations. Here we report the detection of optical light reflected from the dust grains orbiting Fomalhaut (HD 216956). The system is inclined 24° away from edge-on, enabling the measurement of disk structure around its entire circumference, at a linear resolution of 0.5 au. The dust is distributed in a belt 25 au wide, with a very sharp inner edge at a radial distance of 133 au, and we measure an offset of 15 au between the belt's geometric centre and Fomalhaut. Taken together, the sharp inner edge and offset demonstrate the presence of planetary-mass objects orbiting Fomalhaut.