Accurate element readings measured in distant galaxy

Astronomers in California have made the first accurate measurement of the abundance of oxygen in a far off galaxy.

This is important as it will help scientists understand how matter cycles in and out of galaxies. Oxygen — the third most abundant chemical element in the universe — is created inside stars and released when these stars explode into interstellar gas.

Researchers looked at galaxy COSMOS-1908, which contains approximately one billion stars —in comparison the Milky Way contains around 100 billion stars. They found, surprisingly, that COSMOS-1908 contained one-fifth the oxygen observed in the Sun.

Alice Shapley, from the University of California-Los Angeles and co-author, said: “This is by far the most distant galaxy for which the oxygen abundance has actually been measured. We're looking back in time at this galaxy as it appeared 12 billion years ago.”

Astronomers have often relied on indirect and imprecise techniques for estimating oxygen abundance for the vast majority of distant galaxies, but this time direct measurements were taken using methods similar to those used for closer galaxies.

This was achieved using a spectrograph that collected visible light photons from objects billions of light years away that had been redshifted due to the expansion of the universe. Called MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration), this machine allows astronomers to determine the chemical contents of galaxies as different chemical elements emit light at specific wavelengths.

The amount of oxygen in galaxies is dependent on a number of conditions, such as how much oxygen is produced and released from supernovas. Another variable is how much of this oxygen is ejected from the galaxy by ‘super winds’ that can reach hundreds of thousands of miles per hour. Astronomers also consider the amount of pristine gas from the Big Bang that enters the galaxy from the intergalactic medium, which does not contain a lot of oxygen.

Shapley said: “If we can measure how much oxygen is in a galaxy, it will tell us about all these processes. 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.”

The study was published in Astrophysical Journal Letters.