A survey of 37 nearby dwarf galaxies has found that these small, star-forming systems retain only a fraction of the oxygen their stars have produced, according to results from NASA's "GLOW" survey — short for Galaxies Losing Oxygen via Winds — published in two companion papers this week. Researchers combined archival Hubble optical imaging with data from the retired Spitzer Space Telescope, the Very Large Array and the Australian Telescope Compact Array to measure oxygen levels across the sample, and found significantly less than simulations of stellar chemical production predict.
Oxygen is one of the most abundant elements produced by stars, and because its production is well understood, astronomers use it as a reliable tracer of how galaxies chemically enrich themselves and the space around them over time. "Oxygen is one of the primary elements formed by stars," said Kristen McQuinn, the survey's principal investigator and an associate professor at Rutgers University who also leads science operations for NASA's Roman Space Telescope. Grace Telford, a co-investigator and assistant professor at the University of Utah, put it more simply: "Oxygen is produced by stars, which are inside of galaxies."
The leading explanation for the shortfall is that supernova explosions drive galactic winds powerful enough to blow oxygen out of low-mass galaxies more efficiently than current models assume — a process the research, detailed in NASA's own account of the findings, suggests is more pronounced in smaller galaxies than previously appreciated. NASA's release does not give a precise figure for how much oxygen is missing, and it remains unclear whether the lost oxygen sits in a surrounding halo of circumgalactic gas or has been ejected from the galaxy entirely. The work builds on a 2014 study that found even Milky Way-mass galaxies lose substantial oxygen, extending that picture down to much smaller systems.
The findings bear on broader models of galaxy evolution and how galaxies seed the wider universe with the heavy elements needed for later generations of stars and planets. McQuinn said she plans to use NASA's Roman Space Telescope, once launched, to find fainter and smaller dwarf galaxies for further study, while Telford intends to follow up with Hubble observations of individual massive stars as they produce and expel oxygen in small galaxies — work that could clarify exactly where the missing oxygen has gone.
