Galaxy formation and evolution
Silk, Joseph Department of Physics, University of Oxford, Oxford, United Kingdom.
Khochfar, Sadegh Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany.
Last reviewed:February 2019
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- Evidence from structural properties
- Evidence from composition
- Influences of black holes
- Origin of galaxies
- Related Primary Literature
- Additional Reading
How the diverse array of galaxies that are now observed originated and evolved into their present form. Deep telescope observations of the cosmos have found evidence for the first galaxies arising within several hundred million years after the big bang. Since that time more than 13 billion years ago, galaxies have emerged throughout the universe, numbering in the hundreds of billions and often appearing in grand agglomerations known as clusters and in long, vast threads known as filaments. Most galaxies also have evolved to fall into three, broad categories of shape: spiral (with curving internal structures of stars), elliptical (rounded), and irregular (no defined shape) (Fig. 1). Researchers studying galaxy formation and evolution “work backwards” in explaining how galaxies assumed these shapes, predominantly occur in clusters, and have changed as a population over cosmic history. See also: Big bang theory; Cosmology; Galaxy; Universe
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