Detecting structure in a protostellar disk

Spiral structure may provide clues about the early stages of star and planet formation It is now well accepted that stars form from clouds of gas and dust that collapse under their own gravity ( 1 ). However, if all the material fell directly onto the young protostar, it would spin up so much that it would ultimately tear itself apart. Instead, most of the material will initially form a thin, rotationally supported, protostellar disk. On page 1519 of this issue, Pérez et al. ( 2 ) present a high-resolution image of such a disk, using the Atacama Millimeter/submillimeter Array (ALMA). It is this disk that provides mechanisms for transporting angular momentum outward—allowing mass to accrete onto the central protostar—and is the site of planet formation (see the illustration).