An accretion disk is a structure formed by gas and dust in space orbiting around a central object, such as a star, black hole, or neutron star. These disks are often seen in binary systems where one object is pulling material from its companion through gravitational forces. Accretion disks are important in astrophysics because they provide a mechanism for transferring mass and angular momentum in a variety of astronomical systems. They are also thought to play a crucial role in the formation and evolution of stars and black holes. The study of accretion disks involves a range of theoretical and observational techniques, including computer simulations, spectroscopy, and gravitational wave detection.