infalling

Infalling describes the motion of matter moving inward toward a central region, usually under gravity. The term is used across disciplines but is most common in astronomy and physics, where it denotes gas, dust, or even solid bodies flowing toward a forming or accreting object.

In astrophysics, infalling material is a key stage in star formation and in accretion onto compact objects. In a collapsing molecular cloud, gas moves toward the center to build a protostar, often through an infalling envelope and a developing accretion disk. The rate and geometry of infall influence the growth of the central mass and the energetics of the system.

Observationally, infall is inferred from spectral line profiles that show redshifted absorption against a continuum or background emission, known as inverse P Cygni profiles, as well as from velocity-resolved maps.

Near compact objects such as black holes, neutron stars, or white dwarfs, infalling matter forms an accretion flow or disk and releases energy as radiation, jets, or winds.

In general relativity, an observer or object moving inward toward a black hole is called infalling; such motion is described as free fall in the curved spacetime, with proper time to the horizon finite for the observer.

Outside astronomy, infalling can describe particles or debris entering a region influenced by a stronger gravity source or central mass, highlighting the broad use of the concept to indicate inward movement toward a central attractor.