akretion

Akretion is a term that is sometimes used as a variant spelling or historical form of accretion, the process by which matter gradually accumulates onto a body. In contemporary scientific writing, the more common term is accretion, but akretion may appear in older texts or in specific linguistic contexts. The central idea across uses is growth or buildup by the gradual addition of material or energy.

In astronomy, akretion refers to the growth of astronomical objects through gravitational attraction of surrounding gas, dust, or stellar material. Material often moves through an accretion disk, a rotating structure that helps transport angular momentum outward while matter spirals inward toward a central object such as a forming star, a white dwarf, neutron star, or black hole. The infalling material releases energy as electromagnetic radiation, making accreting systems bright in X-ray, ultraviolet, or optical wavelengths. The rate of accretion, or accretion luminosity, is a key physical parameter and is limited in many contexts by the Eddington limit.

In planetary science and geology, accretion describes growth by particle adhesion and coalescence, from dust grains sticking together in protoplanetary disks to the gradual buildup of sedimentary layers or planetary cores through collision and fusion of smaller bodies.

Related concepts include Bondi accretion, disk accretion, and Roche-lobe overflow in binary systems. Akretion, when used, generally carries the same meaning as accretion, with variance primarily in historical or linguistic usage rather than in core physics.