Radiatively Driven Wind

Radiatively driven wind is an outflow of gas accelerated by the pressure of electromagnetic radiation from a luminous central object. The mechanism operates in accretion disks around massive stars and active galactic nuclei, where the radiation field is intense enough to overcome gravity and drive material outward.

The process is governed by the Eddington limit: when the radiation pressure exceeds the gravitational pull, material is launched. In practice, winds are driven by line opacity — the scattering of photons by spectral lines in the outflowing gas — which can be orders of magnitude more efficient than continuum scattering. This is the line-driven wind mechanism, which dominates in hot stars and AGN accretion disks.

Radiatively driven winds are distinct from magnetically driven winds such as the disk winds produced by the Blandford-Payne process. The two mechanisms can operate simultaneously in the same object, with radiative driving dominating at small radii and magnetic driving at larger radii.

The radiatively driven wind is often studied in stellar astrophysics and treated as unrelated to AGN outflows. This separation is artificial. The Eddington limit is universal; the line-driving mechanism is the same; and the coupling between wind and accretion follows the same organizational principles regardless of whether the central object is a star or a black hole.