A disk of gas orbiting a star or black hole is commonly referred to as an accretion disk. An accretion disk is a structure formed by material in orbit around a central object, such as a star or black hole, that is slowly being drawn in by the object's gravitational pull. Accretion disks play a crucial role in the process of accretion, which is the accumulation of material onto a massive object. This process is responsible for powering some of the most energetic phenomena in the universe, such as quasars and X-ray binaries. One of the key features of accretion disks is their ability to generate intense radiation as the material in the disk spirals inward and heats up due to friction and other processes. This radiation can provide valuable insights into the properties of the central object and the surrounding environment. Accretion disks are found in a wide range of astrophysical systems, from young stellar objects to supermassive black holes at the centers of galaxies. Studying these disks can therefore help astronomers better understand the formation and evolution of stars, galaxies, and other cosmic structures. For more information on accretion disks and their role in astrophysics, you can visit websites such as [NASA's Chandra X-ray Observatory](https://www.chandra.harvard.edu/) or [the European Space Agency's XMM-Newton mission](https://www.cosmos.esa.int/web/xmm-newton). These resources offer a wealth of information on the latest research and discoveries related to accretion disks and their implications for our understanding of the universe. In conclusion, an accretion disk is a disk of gas and other material orbiting a star or black hole. These disks are essential for the process of accretion and can provide valuable insights into the nature of the central object and its surroundings. By studying accretion disks, astronomers can gain a deeper understanding of the processes that shape the cosmos and drive some of the most extreme phenomena in the universe.

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