Free Astronomy Magazine September-October 2016

SPACE CHRONICLES oxygen that is observed in the Sun. Typically, astronomers rely on ex- tremely indirect and imprecise tech- niques for estimating oxygen abun- dance for the vast majority of dis- tant galaxies. But in this case, UCLA researchers used a direct measure- ment, said Ryan Sanders, astronomy First accurate measurement of oxygen in distant galaxy U CLA astronomers have used the W. M. Keck Observatory on Maunakea, Hawaii to make the first accurate measure- ment of the abundance of oxygen in a distant galaxy. Oxygen, the third-most abundant chemical ele- ment in the Universe, is created in- side stars and released into inter- stellar gas when stars die. Quantify- ing the amount of oxygen is key to understanding how matter cycles in and out of galaxies. “This is by far the most distant galaxy for which the oxygen abun- dance has actually been measured,” said Alice Shapley, a UCLA professor of astronomy, and co-author of the study. “We’re looking back in time at this galaxy as it appeared 12 bil- lion years ago.” Knowing the abundance of oxygen in the galaxy called COSMOS-1908 is an important stepping stone toward allowing astronomers to better understand the population of faint, distant galaxies observed when the Universe was only a few billion years old, Shapley said. COS- MOS-1908 contains approximately one billion stars. In contrast, the Milky Way contains approximately 100 billion stars. Furthermore, COS- MOS-1908 contains approximately only 20 percent the abundance of by Keck Observatory G alaxy COSMOS-1908 is in the center of this Hubble Space Telescope image, indicated by the arrow. Nearly everything in the image is a galaxy. [Ryan Sanders and the CANDELS team]