
A rotating disk of gas and dust around a central massive object, often a site of accretion.A gas disk is a rotating, flattened structure of gas and dust that forms around a central massive object, such as a young star, a black hole, or a galaxy's center. These disks are fundamental to astrophysics because they are the primary sites where matter accretes onto the central object, and they also serve as the birthplaces of planets. The disk's rotation and internal dynamics govern how material spirals inward, releasing gravitational energy and often producing intense radiation.
The concept of accretion disks was developed in the mid-20th century, with key theoretical work by Soviet physicist Yakov Zeldovich and others in the 1960s, and later refined by Nikolai Shakura and Rashid Sunyaev in 1973.
Gas disks are held in a delicate balance between gravity pulling matter inward and centrifugal force from rotation pushing it outward. Friction and turbulence within the disk cause angular momentum to be transported outward, allowing gas to slowly lose energy and drift inward toward the central object. This process, called accretion, converts gravitational potential energy into heat, making the disk glow across many wavelengths, from infrared to X-rays.
Gas disks are studied to understand planet formation, black hole growth, and the evolution of galaxies; observations of disks around young stars guide the search for exoplanets.
The dust in gas disks can be sculpted into rings and gaps by young planets, as seen in the disk around the star PDS 70, where a forming planet has carved a dust ring.







