Accretion is the process of accumulating material, such as dust, gas, and other particles, onto a larger object. This process is commonly seen in astronomy, as planets, stars, and other celestial bodies form and grow in size due to the accumulation of material from their local environment. Accretion can also occur in other fields such as geology, where material is deposited on the surface of an object over time.
The concept of accretion in astronomy has been around since at least the late 19th century, when Charles Darwin proposed that the Moon was formed from the debris of a collision between the Earth and a large object. This idea, which came to be known as the Giant Impact Hypothesis, was later developed by George Darwin and others in the early 20th century. By the 1950s, accretion had become an accepted model for the formation of planets, stars, and other large bodies.
Today, accretion is a well-studied phenomenon that has been used to explain the formation of planetary systems, stars, galaxies, and other large bodies in the universe. In particular, the accretion disk model has been very successful in explaining the formation of stars and protoplanetary disks around them. Accretion is also a key component of star formation, as the mass of a star increases over time due to the accumulation of material from its local environment.
Accretion has been studied in a variety of contexts, and many different models and theories have been developed to explain its processes. For example, the Cataclysmic Variable Star Model is used to explain the behavior of certain binary star systems, while the Bondi–Hoyle Model is used to explain the accumulation of material onto black holes. Other models, such as the Toomre Instability Model, are used to explain the formation of spiral galaxies and other large structures in the universe.
For further reading, the following journal articles provide more information on the topic of accretion:
Blandford, R. D. & Begelman, M. C. (1999). Accretion onto compact objects: Some theoretical implications. Reviews of Modern Physics, 71(2), pp. S360-S373.
Shu, F., Adams, F. & Lizano, S. (1987). Star formation in molecular clouds: Observations and theory. Annual Review of Astronomy and Astrophysics, 25(1), pp. 23-81.
Zhang, W. & Gammie, C. F. (2003). Accretion disk structure and evolution in active galactic nuclei. Annual Review of Astronomy and Astrophysics, 41(1), pp. 549-599.