January 9, 2003: Researchers using NASA's Hubble Space Telescope believe they are seeing the conclusion of the cosmic epoch where the young galaxies started to shine in significant numbers. This marks a time when the so-called "Dark Ages" of the universe was completed, about 13 billion years ago (based on an estimate of 14 billion years for the current age of the universe).See the rest:
The arrows in this Hubble image indicate three of the 30 objects that astronomers discovered using Hubble's new Advanced Camera for Surveys. Astronomers believe that these numerous objects are faint, young star-forming galaxies that existed when the universe was less than a billion years old. This is right around the cosmic epoch where astronomers believe that radiation from hot stars in numerous young galaxies was converting the universe's cool hydrogen into a hot glowing gas.
Current theory holds that after the big bang that created the universe, there was a time of expansion and cooling that led to what is known as the Dark Ages in cosmic terms. The universe cooled sufficiently for protons and electrons to combine to form cool hydrogen atoms and block the transmission of light. This epoch started about 300,000 years after the big bang, and may have ended about a billion years later. Stars and galaxies started to form at some point during this era, but the omni-present cool hydrogen in the universe absorbed the ultraviolet light produced by stars and cannot be seen by current telescopes.
This was an important transition in the evolution of the universe. Because glowing hydrogen does not absorb ultraviolet light as easily as cool hydrogen, the Dark Ages came to an end when enough hot stars had formed that their ultraviolet light pervaded the universe and re-energized the cool hydrogen, causing it to glow. The shining stars opened a window for astronomers to look very far back into time.
Credit: NASA, H.-J. Yan, R. Windhorst and S. Cohen (Arizona State University)