A protoplanetary disk is a rotating disk of dense gas and dust that surrounds a newly formed star. These disks are the birthplaces of planets, as the material within them gradually comes together to form planetesimals, which then coalesce to form planets. Protoplanetary disks are often observed using telescopes and other astronomical instruments, providing valuable insights into the processes of planet formation and the early stages of planetary systems. These disks typically have a lifespan of a few million years before they dissipate, leaving behind fully formed planetary systems.