Gasakkretion

Gasakkretion is the process by which gas is gravitationally captured and accumulated by a celestial body. In astrophysics, it is a fundamental mechanism for the growth of stars, planets, and accreting compact objects, and it occurs in diverse environments from molecular clouds to galactic centers.

In star formation, gas from a collapsing molecular cloud feeds a protostar and its surrounding accretion disk. The rate of accretion depends on gas density and temperature, as well as magnetic fields and turbulence. Feedback from the growing star, such as winds and radiation, can regulate or stop accretion.

In planet formation, gas accretion describes the capture of gas from the protoplanetary disk by a growing planetary core. After reaching a sufficient core mass, a planet can enter a rapid, runaway gas accretion phase, forming a gas giant. Accretion stops or slows when the disk dissipates, when the planet opens a gap in the disk, or when heating from accretion reduces envelope growth.

In accreting compact objects like black holes, gas accretion proceeds through a disk in which angular momentum is transported outward. The accretion rate often approaches a limiting luminosity known as the Eddington limit; regimes below or above this limit yield different radiative efficiencies and spectral states. Theoretical models include quasi-spherical Bondi accretion and disk accretion governed by viscosity and magnetic stresses.

Observationally, gas accretion manifests as characteristic emission across the electromagnetic spectrum and as dynamical infall signatures in disks, envelopes, or filaments around galaxies, stars, or planets.