This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists examining data collected by NASA's Hubble Space Telescope have found that dozens of small galaxies contain far less oxygen than their stars are estimated to have produced. The researchers, including a Rutgers astrophysicist, studied 37 dwarf galaxies, which are much smaller than the Milky Way and considered to be nearby, within 22 million light-years of Earth.
The results were published in The Astrophysical Journal. Members of the team compared estimates of how much oxygen the galaxies' stars had made over their lifetimes with the amount remaining in the galaxies' stars, gas and dust. The galaxies retained between 4% and 25% of the oxygen, with an average of about 11%.
Tracking oxygen helps scientists understand how galaxies change over time and how elements made by stars spread through the universe. Oxygen, the most abundant element in the universe after hydrogen and helium, is relatively easy to detect and measure, according to scientists. That makes it a useful clue to the movement of other elements produced by stars.
"Oxygen is one of the primary elements formed by stars," said Kristen Wingfield McQuinn, an associate professor in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences and a co-author of the study. "So, it's really for practical reasons that we've chosen oxygen." Oxygen gives off light at specific colors that instruments on telescopes on Earth can easily detect. By separating that light into its different colors and measuring its brightness, scientists can identify oxygen and estimate how much is present.
McQuinn leads the Galaxies Losing Oxygen via Winds (GLOW) project, which examines how much oxygen stars produce, how much their galaxies keep and how much escapes into surrounding space. The findings suggest galactic winds, streams of gas driven outward by energy from massive stars and stellar explosions, remove oxygen more effectively than current computer models predict. These explosions, called supernovae, occur when certain stars reach the end of their lives.
"We know that the oxygen had to be inside of the galaxies at some point in the past, so the oxygen must have been ejected," said Grace Telford, an assistant professor in the Department of Physics and Astronomy at the University of Utah and a coinvestigator in the study. "And to do that, you need energy from massive stars and supernova explosions to drive material out of the host galaxies and into the space between galaxies." The researchers used previously collected images from Hubble to distinguish individual stars within the galaxies. The stars' brightness and colors helped researchers piece together when the galaxies formed stars and how their chemical makeup changed.
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