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physical phenomena > process > physical process > motion > mass motion > contraction

contraction
subject			fact

contraction	has definition A mass motion towards the center of gravity of a celestial body
	is a kind of mass motion
physical process	has domain physics

Kinds of contraction :

• accretion (3 facts) - Collection of material together, generally to form a single body., A process by which a star accumulates matter as it moves through a dense cloud of interstellar gas; or, more generally, whereby matter surrounding a star flows toward it (as in close binaries).
• collapse (5 kinds, 14 facts) - Sudden contraction of a celestial body
• gaseous fragmentation (2 facts) - The systematic breakup of a gas cloud into smaller and smaller subunits as the gas cools and continues to collapse. The gravitational forces continually overtake the opposing pressure gradients as long as the cloud is able to radiate freely; consequently, the Jeans mass decreases, and fragments divide into smaller subfragments. The process stops only when opacity intervenes to inhibit the cooling and radiation.
• Kelvin contraction (3 facts) (Kelvin-Helmholtz contraction) - The contraction of a star contemplated by Kelvin and Helmholtz as a consequence of a star's radiating its thermal energy. It is currently believed that the contraction of a star occurs in this manner in its pre-main-sequence evolution.
• pancake model (2 facts) - A model of galaxy formation in which the first structures to condense out of the smooth background of primordial gas were very large in size. These large masses then collapsed into thin sheets (pancakes) and fragmented into many smaller pieces the size of galaxies. A competing theory, sometimes called the hierarchical clustering model, proposes that the first structures to form were the size of galaxies. As galaxies clustered together, due to gravity, larger and larger structures were formed. (See hierarchical clustering model.)