Abstract
Planet formation is one of the hottest topics in the 21st century astrophysics. It is well known that disks are formed around young stars in the course of star formation, and planets are formed in these disks. Recent high angular resolution observations have revealed that many of disks around pre-main-sequence (PMS) stars have substructures, such as gaps or rings, which are signs of ongoing planet formation or even hidden protoplanets. Ubiquitous substructures in disks around PMS stars may suggest that planet formation has initiated in a stage earlier than the PMS phase, i.e., the protostellar phase. In order to probe the earliest stage of planet formation, we have to observe younger disks around protostars. With this motivation we have carried out the Large Program “Early Planet Formation in Embedded Disks (eDisk)” using Atacama Millimeter and submillimeter Array (ALMA) to systematically observe disks around 19 protostellar systems in nearby (d < 200 pc) star forming regions at a resolution of ~7 au. The Large Program has two main scientific objectives; (1) to search for substructures in disks around protostars, exploring possible early planet formation around protostars, (2) to search for Keplerian motions in disks, enabling to derive dynamical masses of the central protostars. The observations made in 1.3 mm continuum emission have revealed that disks around protostars have less distinctive substructures and more brightness asymmetries in marked contrast to disks around PMS stars. This remarkable difference in disks between protostars and PMS stars may suggest that planet formation quickly progresses when protostars evolve into PMS stars. In this talk, I will describe more details of the eDisk program, including its background, and will highlight initial results of the program.