Once the star has formed from a molecular cloud, planets can form around it from the remnants of the disk of matter which gave birth to it. These disks are called planetary or protoplanetary disks, in reference to the disks of matter which exist before the disks that follow the planetary orbits of a star system.
The astrophysicist Vincent Minier explains how planetary disks are formed and structured.
For more information: The process whereby planets emerge from protoplanetary disks around a young star (called a proto-star) has not yet been fully understood. It is particularly difficult to comprehend the very first steps in their evolution, from individual grains to bodies several kilometres in diameter. The observation of several protoplanetary disks is therefore valuable in understanding the initial stages in the formation of planets. This has only recently become possible, with the arrival of new telescopes such as ALMA, which carry out observations using radio waves. It was only in 2018 that a protoplanet was viewed for the first time directly, with no image reconstruction, as is the case with radio waves. This was done using the SPHERE infrared instrument coupled to the VLT. And very recently, astronomers have succeeded in imaging a young system in formation with a spiral structure in the disk, showing the site where a planet could form