Starlit galaxies were born in the very ancient Cosmos, and they began to illuminate it less than a billion years after its Big Bang birth almost 14 billion years ago. The prevailing theory of galaxy formation suggests that the most ancient galaxies were only a small fraction of the size of our own large, mature, barred-spiral Galaxy, the Milky Way--but they were just as brilliant, because they were vigorously giving birth to a myriad of searing-hot, active, sparkling baby stars. In July 2014, a team of astronomers studying the behavior of the Universe shortly after the Big Bang, reported that they have made a surprising observation: their research suggests that the properties of the ancient Universe were determined by the smallest and faintest galaxies. The team reports their findings in a paper published on July 7, 2014 in the journal Monthly Notices of the Royal Astronomical Society.
Most astronomers think that the Cosmos was fully re-ionized approximately one billion years after the Big Bang. Ionization is the process by which an atom acquires a negative or positive charge as the result of either the loss or the gain of electrons. About 200 million years after the Universe's Big Bang beginning, ultraviolet (UV) radiation emitted by the first generation of stars began to split neutral hydrogen into negatively charged electrons and positively charged protons. It took another 800 million years for this process to be completed all over the ancient Cosmos. This epoch of re-ionization heralded the last major alteration in the Universe's supply of gas, and it remains ionized to this very day--more than 12 billion years later!
However, astronomers are not in general agreement about which of the various types of galaxies, dancing around in the early Universe, proved to be the primary player in this great, and very ancient Cosmic drama. Most astronomers have focused on the larger galaxies dwelling in the early Universe. However, the new study conducted by researchers at the Georgia Institute of Technology and the San Diego Computer Center, both located in the United States, suggests that scientific studies should not dismiss the possible influence of the smallest galactic denizens of our Cosmos, as well.
The astronomers used new supercomputer simulations to show how the smallest, dimmest galaxies dwelling in the ancient Cosmos may have made it what it is today. These petite galaxies, even though they were approximately 30 times tinier in size and 1000 times smaller in mass than our Milky Way Galaxy--contributed as much as 30 percent of the blasts of UV light during this ancient process.
Earlier studies ignored these faint, tiny dwarf galaxies, assuming that they were unable to give birth to fiery baby stars. This is because it was believed that the UV light from nearby larger galaxies was too powerful and, as a result, suppressed their smaller neighbors' star-forming abilities.
"It turns out these dwarf galaxies did form stars, usually in one burst, around 500 million years after the Big Bang. The galaxies were small, but so plentiful that they contributed a significant fraction of UV light in the re-ionization process," explained Dr. John Wise in a July 7, 2014 Royal Astronomical Society (RAS) in London Press Release. Dr. Wise, who led the new study, is of the Georgia Institute of Technology.