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In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, into an accretion disk. [ 1 ] [ 2 ] Most astronomical objects , such as galaxies , stars , and planets , are formed by accretion processes.
The most prominent accretion disks are those of active galactic nuclei and of quasars, which are thought to be massive black holes at the center of galaxies. As matter enters the accretion disc, it follows a trajectory called a tendex line, which describes an inward spiral. This is because particles rub and bounce against each other in a ...
Pebble accretion is the accumulation of particles, ranging from centimeters up to meters in diameter, into planetesimals in a protoplanetary disk that is enhanced by aerodynamic drag from the gas present in the disk. This drag reduces the relative velocity of pebbles as they pass by larger bodies, preventing some from escaping the body's gravity.
Accretion – Accumulation of particles into a massive object by gravitationally attracting more matter; Age of Earth – Scientific dating of the age of Earth; Big Bang – Physical theory; Chronology of the universe – History and future of the universe; Circumplanetary disk – Accumulation of matter around a planet
The runaway accretion lasts between 10,000 and 100,000 years and ends when the largest bodies exceed approximately 1,000 km in diameter. [20] Slowing of the accretion is caused by gravitational perturbations by large bodies on the remaining planetesimals. [20] [65] In addition, the influence of larger bodies stops further growth of smaller ...
In astrophysics, the Bondi accretion (also called Bondi–Hoyle–Lyttleton accretion), named after Hermann Bondi, is spherical accretion onto a compact object traveling through the interstellar medium. It is generally used in the context of neutron star and black hole accretion. To achieve an approximate form of the Bondi accretion rate ...
Of these, perhaps the most prominent is the theory of competitive accretion, which suggests that massive protostars are "seeded" by low-mass protostars which compete with other protostars to draw in matter from the entire parent molecular cloud, instead of simply from a small local region. [63] [64]
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components: a cosmological constant , denoted by lambda (Λ), associated with dark energy ;