Planet-forming disks

Disks experience an abrupt increase in IR brightness between 2Myr and 5Myr. The earliest IR disk cavities around single stars arise after 2-3Myr explaining why are young disks faint in the near-IR, and determining which disks can live longer. Well-known, high-longevity disks (>8Myr) are always bright.

Ambient material is detected in more than 20% of young sources but the fraction drops with time. We find a clear correspondence for the presence of ambient material with the stellar variability, near-IR excess, and mass accretion rate as well as, in turn, with spirals and shadows in disks. Half of the disks with ambient material show spirals while none of them show rings.

We therefore propose that the spirals and the disk warps responsible for shadows are generally induced by late infall from the medium, and that this also affects the stellar accretion. The emerging picture proves the fundamental role of the environment for the disk evolution and planet formation.