In astrophysics, the term accretion is used for at least two distinct processes. Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ...

The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc. Accretion discs are common around smaller stars or stellar remnants in a close binary, or black holes in the centers of spiral galaxies. Some dynamics in the disc are necessary to allow orbiting gas to lose angular momentum and fall onto the central massive object. Gravity is a force of attraction that acts between bodies that have mass. ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... Artists conception of a binary star system with one black hole and one main sequence star An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Artists impression of a binary system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... A black hole is an object predicted by general relativity[1] with a gravitational field so strong that nothing can escape it — not even light. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Gyroscope. ...

The second process is somewhat analogous to the one in atmospheric science. In the nebular theory, accretion refers to the collision and sticking of cooled microscopic dust and ice particles electrostatically, in protoplanetary discs and Jovian protoplanet systems, eventually leading to planetesimals which gravitationally accrete more small particles and other planetesimals. A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... This siliqua of Jovian, ca 363, celebrates his fifth year of reign, as a good omen. ... In cosmogony, a protoplanet is a quasi-planetoid which is slightly larger than a planetesimal and orbits within a solar nebulas protoplanetary discs. ... In cosmogony, planetesimals are objects thought to exist within solar nebulae. ...

Use of the term accretion disc for the protoplanetary disc thus leads to confusion over the planetary accretion process, although in many cases it may well be that both accretion processes are happening simultaneously (e.g. T Tauri). Drawing of a T-Tauri star with a circumstellar accretion disk T Tauri stars are a class of variable stars named after their prototype - T Tauri. ...

The Jovian protoplanets probably have discs of their own, in close analogy to the solar system as a whole. The Jovian protoplanet may be accreting gas from its surrounding disc in the first process, at the same time that dust and ice particles in the disc are accreting into moonlets and ring systems, in the second process. Major features of the Solar System (not to scale): The Sun, the eight planets, the asteroid belt containing the dwarf planet Ceres, outermost there is the dwarf planet Pluto (the dwarf planet Eris not shown), and a comet. ...