September 7, 2012
Explosion Of Galaxy Growth In The Early Universe
April Flowers for redOrbit.com - Your Universe Online
A new study from the University of California, Berkeley indicates that the birth of the first massive galaxies that lit up the early universe was an explosive event, happening faster and ending sooner than suspected.
Around 13 billion years ago, when the universe was about 750 million years old, extremely bright, active galaxies formed and fully illuminated the universe, according to Oliver Zahn, a postdoctoral fellow at the Berkeley Center for Cosmological Physics (BCCP) at the University of California, Berkeley, who led the data analysis.
This new data, from the South Pole Telescope, provides new constraints on the universe's first era of galaxy formation, called the Epoch of Reionization. Early stars came to life in massive gas clouds, generating the first galaxies, so most astronomers think. The energetic light pumped out by these stars is thought to have ionized the hydrogen gas in and around the galaxies. This created "ionization bubbles" millions of light years across leaving a lasting, telltale signature in the cosmic background radiation (CMB). This relic light from the early universe is visible today everywhere in the sky and was first mapped by UC Berkeley physicist and Nobel laureate George Smoot, founder of the BCCP.
“We find that the Epoch of Reionization lasted less than 500 million years and began when the universe was at least 250 million years old,” Zahn said. “Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began.”
Just after the Big Bang, everything was so hot that all the gas, mostly hydrogen, was ionized during the first epoch of ionization. The universe only cooled enough for electrons to latch onto protons to form neutral hydrogen atoms when the universe was about 400,000 years old.
“Studying the Epoch of Reionization is important because it represents one of the few ways by which we can study the first stars and galaxies,” said study co-author John Carlstrom of the University of Chicago.
The short duration of this epoch suggests that monster galaxies with more than a billion stars played a key role in the reionization, since smaller galaxies would have formed much earlier.
The results are based on a new analysis that combines measurements taken by the South Pole Telescope at three frequencies and extends the measurements to a larger area covering approximately 2 percent of the sky. The 75-foot-tall South Pole Telescope, located at the Amundsen Scott South Pole station in Antarctica, operates at millimeter wavelengths to make high-resolution images of the CMB and its polarization.
The team combined this new data with earlier data from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite and was able to put stringent constraints on when the epoch or reionization began and how long it lasted.
WMAP is a NASA Explorer mission launched to make fundamental measurements of cosmology — the study of our universe as a whole. Though WMAP's transmission has ended, analysis of the data is still ongoing.
“Our data mostly tells you the duration of the Epoch of Reionization, while WMAP mostly tells you when, on average, it happened, so both together tell you the evolution of ionization over time,” Zahn said.
Astronomers were unsure whether they would be able to constrain the Epoch of Reionization using the CMB because of uncertainty over how stars formed, clustered and spewed ionizing radiation into the interstellar medium in the early universe. Over the past decade, however, various groups developed models of these processes. Zahn and his team used them to work backwards to put limits on when the era began and ended.
“In their study of the epoch of reionization, people have been focused on the spectra of distant quasars and galaxies,” said Zahn. “Now the CMB is adding a wealth of information to this field.”
Astronomers expect to learn a great deal more from the South Pole Telescope. The current results are based on only the first third of the full telescope survey. Additional work is underway to combine the telescope's maps with ones made with the Herschel satellite to further increase the sensitivity to the reionization signal.
“We expect to measure the duration of reionization to less than 50 million years with the current survey,” Christian Reichardt, University of Chicago, said. “With planned upgrades to the instrument, we hope to improve this even further in the next five years.”
The South Pole Telescope was specifically designed to detect signals of reionization in the Cosmic Microwave Background, and allow astronomers to measure the extent of the partially ionized phase. The signal came from cosmic background radiation interacting with electrons in the ionization bubbles, which created small hot and cold spots in the CMB based on whether a bubble was moving toward or away from us.