The accretion theory, in astrophysics, is a scientific theory of the formation of our Solar system. 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 astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... Theory has a number of distinct meanings in different fields of knowledge, depending on the context and their methodologies. ... Presentation of the solar system (not to scale) The solar system comprises our Sun and the retinue of celestial objects gravitationally bound to it. ...

The theory maintains that there existed a large, dense cloud of interstellar gas (the solar nebula), which began contracting under the pressure of its own gravity. In order to conserve its angular momentum, the nebula also began rotating, turning into an accretion disc, with a lump of matter accumulating at the center (the protosun). This lump eventually reached the conditions of temperature and pressure needed to initiate nuclear fusion, and became the giant Sun. In cosmogony, the solar nebula is the gaseous cloud (or accretion disc) from which our solar system is believed to have formed. ... Gravity is the force of attraction between massive particles. ... In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ... Artists conception of a binary star system with one black hole and one main sequence star // Overview An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... The protostar period is the period in the evolution of a star after the cloud of hydrogen, helium and dust has started contraction and before the star has reached the main sequence on the Hertzsprung-Russell diagram. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... The Sun (or Sol) is the star at the center of our Solar system. ...

The materials in the rest of the nebula (gas molecules, particles of dust, etc.) slowly clumped into larger conglomerates, which in turn underwent multiple collisions and further condensation, until the planets, satellites and comets were formed.

The accretion theory is the standard model for the formation of the Solar system, and is also considered the likely mechanism for the formation of planetary systems other than ours, such as the ones discovered in recent years. An artists concept of a protoplanetary disk. ...