Editing Cold dark matter (section)

==Structure formation==

In the cold dark matter theory, structure grows hierarchically, with small objects collapsing under their self-gravity first and merging in a continuous hierarchy to form larger and more massive objects.  Predictions of the cold dark matter paradigm are in general agreement with observations of [[Observable universe|cosmological large-scale structure]]. 

In the [[hot dark matter]] paradigm, popular in the early 1980s but less so in the 1990s, structure does not form hierarchically (''bottom-up''), but forms by fragmentation (''top-down''), with the largest [[supercluster]]s forming first in flat pancake-like sheets and subsequently fragmenting into smaller pieces like our galaxy the [[Milky Way]].

Since the late 1980s or 1990s, most cosmologists favor the cold dark matter theory (specifically the modern [[Lambda-CDM model]]) as a description of how the [[universe]] went from a smooth initial state at early times (as shown by the [[cosmic microwave background]] radiation) to the lumpy distribution of [[galaxies]] and their [[galaxy cluster|clusters]] we see today—the large-scale structure of the universe. [[Dwarf galaxies]] are crucial to this theory, having been created by small-scale density fluctuations in the early universe;<ref>{{cite journal
 |url          = http://www.aanda.org/
 |title        = The C star population of DDO 190: 1. Introduction
 |first        = P.
 |last         = Battinelli
 |author2      = S. Demers
 |date         = 2005-10-06
 |publisher    = Astronomy & Astrophysics
 |page         = 473
 |doi          = 10.1051/0004-6361:20052829
 |archive-url  = https://web.archive.org/web/20120815011424/http://www.aanda.org/
 |archive-date = 2012-08-15
 |access-date  = 2012-08-19
 |quote        = Dwarf galaxies play a crucial role in the CDM scenario for galaxy formation, having been suggested to be the natural building blocks from which larger structures are built up by merging processes. In this scenario dwarf galaxies are formed from small-scale density fluctuations in the primeval universe.
 |bibcode      = 2006A&A...447..473B
 |volume       = 447
 |journal      = Astronomy and Astrophysics
 |issue        = 2
 |doi-access   = free
 |url-status   = bot: unknown
|url-access= subscription
 }}</ref> they have now become natural building blocks that form larger structures.