An international team of astronomers has pushed the limit of observational astronomy even further. Using the Atacama Large Millimeter Array (ALMA) in Chile, the researchers were able to detect light from ionized oxygen in a galaxy 13.1 billion light-years away, making it the most distant oxygen ever detected.
The light of this galaxy comes to us all the way from the epoch of reionization, a still mysterious period of the universe when the first stars and then the first galaxies formed. New instruments like ALMA have begun to probe this age, and we are understanding more and more about it.
The observations of this galaxy, which are reported in Science, show that the object called SXDF-NB1006-2 has about 10 percent the ratio of oxygen to other gases we see in galaxies today. Surprisingly the galaxy has very little carbon and dust.
"Seeking heavy elements in the early universe is an essential approach to explore the star formation activity in that period," said Akio Inoue of Osaka Sangyo University, and lead author of the research, in a statement.
The heavy elements we have found in the universe today, such as carbon, oxygen, and iron, did not form in the Big Bang but were the result of stars. The first stars formed in the first few hundred million years and died very quickly, enriching the universe with new elements.
The light of the first stars was so strong that it ripped electrons from the hydrogen gas in the universe, ionizing hydrogen for the second time in the history of the universe (thus the name reionization). We are yet to see these stars, though, so we are looking for their effect on the early universe.
"This is the first step to understanding what kind of objects caused cosmic reionization," explained Yoichi Tamura of the University of Tokyo.
"Our next observations with ALMA have already started. Higher resolution observations will allow us to see the distribution and motion of ionized oxygen in the galaxy and provide precious information to understand the properties of the galaxy."
"Something unusual may be happening in this galaxy," added Inoue. "I suspect that almost all the gas is highly ionized."
The lack of dust and carbon is likely the reason why almost all the gas is ionized; without being absorbed the energetic photons of the young bright stars reach intergalactic space and ionize gas there as well. Objects like SXDF-NB1006-2 could be the main engine behind cosmic reionization, and studying them will provide a unique window into the early universe.