Cosmological Structure Formation
Cosmological Structure Formation
The minute temperature fluctuations in the CMB are directly responsible for the complex large-scale structure in today's Universe. Scientists are still on the quest toward understanding how these small fluctuations evolve into the galaxy clusters and filaments we see today.
The temperature fluctuations in the WMAP may be thought of as density fluctuations in the early Universe. These slight differences in density become amplified by gravity. Regions that are more dense, even by tiny amounts, will gradually collapse because of this excess gravity. This process, called gravitational instability, worked slowly over billions of years until galaxies formed. Those galaxies are now hundreds of times denser than the nearly empty space that surrounds them.
In addition to galaxy-sized objects, this process gave rise to clusters and filamentary strands of galaxies. The structure of the Universe is akin to human settlement in the world. We settle in towns of various sizes (a galaxy) and these towns often cluster around each other (a galaxy cluster). Connecting these towns are trails, rivers, and highways, along which smaller towns or groups of towns are found (galaxy filaments).
While galaxy groups and clusters are gravitationally bound systems such that no galaxy can escape, superclusters have not yet settled into this state. In our analogy, this would be similar to the major cities in the Northeast United States. From Washington, D.C., to New York, one can travel from town to town almost without leaving an urban area. Interstate 95 connects them all as one area. But this urban region has not yet merged into one large megalopolis, just as a supercluster has not yet become gravitationally bound.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott