Accreting

Accreting is the act of growth by accumulation of matter or other material. In general use, it refers to a body gradually gaining mass as material adheres or is gravitationally captured. As an adjective, accreting describes objects currently undergoing such growth.

In astronomy, accretion is a fundamental growth process. In star and planet formation, gas and dust in a protoplanetary disk spiral inward toward a central protostar or protoplanet, forming an accretion disk. Material loses angular momentum and falls onto the central object, releasing energy as radiation. The rate of accretion influences luminosity and evolution.

Near white dwarfs, neutron stars, and black holes, accretion disks can become hot and emit X-rays; flickering and quasi-periodic oscillations reflect changes in the inner disk. The Eddington limit constrains the maximum steady luminosity for a given mass.

Pebble accretion and planetesimal accretion describe growth of planetary cores; once enough mass is accumulated, gas accretion can form giant planets.

Accretion also occurs in other systems: the accretion of material onto planetary bodies, the growth of satellites, and crystallization or material growth in solids, where particles adhere to surfaces and the structure enlarges over time.