The case of the missing oxygen: Hubble research highlights mystery

Nov. 2 (UPI) — Researchers using NASA’s Hubble Space Telescope to study nearby dwarf galaxies discovered a puzzle: Those galaxies have far less oxygen than expected.

In a study published Monday in The Astrophysical Journal, scientists said they studied 27 dwarf galaxies and found that, although simulations predicted those galaxies should have significant amounts of oxygen, they actually had far less.

“Oxygen is produced by stars, which are inside of galaxies,” said Grace Telford, co-investigator and assistant professor in the Department of Physics and Astronomy at the University of Utah, to NASA. “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. 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 new study shows that galactic winds seem to be far more effective at removing oxygen from these small galaxies than predicted.

The researchers in the Galaxies Losing Oxygen via Winds project, which is funded by NASA and the National Science Foundation, studied oxygen to better understand its role in space, including how it’s distributed. Scientists said oxygen was a practical choice: It is a reliable indicator of how elements are spread out in galaxies and is relatively easy to find and measure.

“Oxygen is one of the primary elements formed by stars,” said Kristen Wingfield McQuinn, principal investigator for GLOW and mission head of the Science Operations Center for the NASA Nancy Grace Roman Space Telescope at the Space Telescope Science Institute in Baltimore. “Being able to trace how much oxygen gets made, and then how much is distributed inside and outside of galaxies, helps us understand galaxy evolution.

“It also helps us learn where and how much galaxies are enriching the space between galaxies, called the intergalactic medium.”

A previous study showed that, for star-forming galaxies like our own Milky Way, some of the missing oxygen is found in the diffuse haloes of gas surrounding galaxies outside their discs, which is called the circumgalactic medium. It’s still unclear if most of the missing oxygen is in this medium for the dwarf galaxies or if it’s been completely ejected.