Elementary Cosmology: From Aristotle's Universe to the Big Bang and Beyond by James J Kolata

Author:James J Kolata
Language: eng
Format: epub
ISBN: 9781681741000
Publisher: IOP Publishing
Published: 2015-11-19T05:00:00+00:00

9.1.6 Later frames

The time of nucleosynthesis was now over and the hectic pace of the evolution of the Universe slowed down. As mentioned earlier, the Universe became matter dominated at t = 50 000 years and photons decoupled at t = 400 000 years. The Dark Ages of cosmology follow that event. During this period, stars had not yet formed and the only radiation visible would have been that emitted from heated neutral hydrogen gas. Eventually, however, galaxies and stars formed via the gravitational collapse of the density fluctuations in the CMB previously mentioned. (The origin of these fluctuations will be discussed later on.) This is estimated to occur at about 200–400 million (2–4 × 108) years after the Big Bang, initiating the era know as reionization which extends to the present. Galaxies born at only about 4 × 108 years after the Big Bang have already been seen using the HST, but that is at the limit of its sensitivity. The James Webb Telescope (launch date currently estimated as 2018) will have the power to probe this era in detail and observe the formation of the earliest galaxies.

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