Free Astronomy Magazine September-October 2023

49 SEPTEMBER-OCTOBER 2023 ASTRO PUBLISHING tary disks show such signs, suggest- ing that planet formation is already in progress or has almost completed in the systems we typically refer to as ‘protoplanetary disks’. “These previ- ous results motivated us to examine even younger disks around proto- stars to answer the question, at what stage of star formation do planet forms,” says Ohashi. With this motivation, the team fo- cused on disks around protostars, systems that are only 10,000 to 100,000 years old, and observed the radio emission emitted from dust grains, i.e., the building blocks of planets, in disks with ALMA. Previ- ous studies have only observed a small handful of protostars with the resolution necessary to detect signs of planet formation. The international team observed disks around 19 protostars located within about 650 light-years from the Earth utilizing the very high an- gular resolution of ALMA to exam- ine the structure of the protostellar disks in detail. This is the first system- atic study to investigate the detailed structure of disks around a large sample of protostars with such a high angular resolution. The observations confirmed that there are disks around all the proto- stars, meaning that the minimum conditions for planet formation are already present in these young pro- tostar systems. However, the obser- vations clearly show that the disks around protostars are different from more-evolved protoplanetary disks. Among the 19 protostars, rings, and gaps, which are signs of planet for- mation, were observed only in a few disks toward the most evolved pro- A rtistic image of a disk around a protostar. [ALMA (ESO/NAOJ/NRAO)]