Density contrast is a parameter used in
galaxy formation to indicate where there are local enhancements in matter density.
:
It is believed that after
inflation, although the universe was mostly uniform, some regions were slightly denser than others with contrast densities on the order of 1 trillionth. As the
horizon distance expanded, the enclosed causally connected (i.e. gravitationally connected) masses increased until they reached the
Jeans mass
In stellar physics, the Jeans instability causes the collapse of interstellar gas clouds and subsequent star formation, named after James Jeans. It occurs when the internal gas pressure is not strong enough to prevent gravitational collapse of a ...
and began to collapse, which allowed
galaxies,
galaxy clusters
A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second- ...
,
superclusters
A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in turn ...
, and
filaments to form.
References
Physical cosmology
Inflation (cosmology)
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