Atomic Fog Shrouded Early ‘Dark Age’ of the Universe
The discovery of a small but distant galaxy 12.8 billion light years from Earth in 2011 provided important clues about the earliest years of the universe’s life. By measuring the age of the galaxy’s stars using gravitational lensing, astronomers in Europe and the US found that the galaxy began to shine when the universe was just 150–300 million years old, which hints that these galaxies were responsible for dispersing the atomic fog that shrouded the early cosmos, during a period in the history of the universe that astronomers refer to as the “dark age.”
After the Big Bang, 13.7 billion years ago, the universe was hot and ionized. But as the universe expanded, it cooled, and 380,000 years after the Big Bang, protons joined electrons to make neutral hydrogen atoms, which block light. As stars and galaxies evolved whose radiation ionized the universe anew, allowing light to speed through space unimpeded – a period dubbed the epoch of re-ionization.
Astronomers’ knowledge of this ancient era is limited because the light from galaxies that existed then has traveled for almost 13 billions years and is therefore extremely faint when it reaches Earth. But a new study by Johan Richard of the University of Lyon in France and his colleagues have spotted a ancient, distant galaxy that appears much brighter, due to gravitational lensing.
“What makes this object very special is that we can really get a very strong signal on a very faint object,” said Richard.
When light from very distant bodies passes through the gravitational field of much nearer massive objects, it bends in an effect known as “gravitational lensing.” In a pioneering technique, a Caltech-led group used massive clusters of galaxies—the best example of natural gravitational lenses—in a series of campaigns to locate progressively more distant systems that would not be detected in normal surveys.