Oxygen keeps us alive and keeps fires burning. But when it comes to space, we can use oxygen to study how galaxies evolve. And now astronomers can look for it all the way in the very early universe.
Using the W. M. Keck Observatory on Mauna Kea, Hawaii, astronomers from the University of California, Los Angeles, were able to estimate the oxygen content in the galaxy COSMOS-1908, which is located a whopping 12 billion light-years from Earth. The galaxy, which is producing 50 times more stars than the Milky Way, has the same ratio of oxygen to hydrogen found in galaxies in the local universe.
"This is by far the most distant galaxy for which the oxygen abundance has actually been measured," said professor Alice Shapley, co-author of the study describing the findings in the Astrophysical Journal Letters, in a statement. "We're looking back in time at this galaxy as it appeared 12 billion years ago."
Oxygen is the third most abundant element in the universe (after hydrogen and helium), making up 1.04 percent of all visible matter. It is produced in the core of stars towards their later years, and it is dispersed and moved around galaxies in several ways.
Supernovae spread heavy elements across a galaxy, with the amount of oxygen that escapes from these exploding stars influencing the total abundance we observe. The abundance also depends on how much oxygen is pushed into intergalactic space by the “super-wind” generated by many supernovae exploding near each other, as well as by supermassive black holes. Hydrogen and helium falling into the galaxy from the outside can dilute the amount of oxygen we observe.
Supernovae, galaxy-wide super-winds, and in-falling gas are key features in the evolution of young galaxies. Understanding the process gives us a window into galaxy evolution itself.
"If we can measure how much oxygen is in a galaxy, it will tell us about all these processes," said Shapley. "Measuring the oxygen content of galaxies over cosmic time is one of the key methods we have for understanding how galaxies grow, as well as how they spew out gas into the intergalactic medium."
COSMOS-1908's relative abundance of oxygen suggests that these processes must have been active for many millions of years, and hopefully new instruments will probe oxygen abundances even further back in the universe.
