NASA's Hubble Space Telescope has revealed a mystery in our cosmic neighborhood: nearby dwarf galaxies hold onto only a small fraction of the oxygen their stars produced. The result comes from the GLOW (Galaxies Losing Oxygen via Winds) project, funded by NASA and the National Science Foundation, and was published on November 2, 2026, in The Astrophysical Journal.
The team studied 37 dwarf galaxies within about 22 million light-years of Earth — systems with a few thousand to hundreds of millions of stars, far smaller than the Milky Way. By comparing how much oxygen the stars in these galaxies made over their lifetimes with the oxygen still present in their stars, gas and dust, the researchers found they retained only between 4% and 25% of the oxygen, averaging about 11%. Nearly all of the oxygen that remains sits in the gas, not in stars or dust.
“Oxygen is produced by stars, which are inside of galaxies. 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, a co-investigator on the study and assistant professor in the Department of Physics and Astronomy at the University of Utah. “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.”
Galactic winds stronger than models predicted
Simulations already predicted that dwarf galaxies would lose much of their oxygen, but the observations showed an even greater loss: supernova-driven galactic winds appear to remove oxygen from low-mass galaxies more effectively than current models predict. Oxygen was chosen as the tracer because it is the most abundant element after hydrogen and helium, is relatively easy to detect and measure, and its production is well understood.
“Oxygen is one of the primary elements formed by stars. 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,” said Kristen Wingfield McQuinn, GLOW principal investigator, associate professor at Rutgers University and mission head of the Science Operations Center for NASA's Nancy Grace Roman Space Telescope at the Space Telescope Science Institute. “It also helps us learn where and how much galaxies are enriching the space between galaxies, called the intergalactic medium.”
Where did the oxygen go?
It is still unclear where the lost oxygen ended up. A 2014 study of Milky Way-like galaxies found some of that oxygen in the diffuse gas halos surrounding galaxies, known as the circumgalactic medium. For dwarf galaxies, however, it remains open whether most of the missing oxygen sits in those halos or was ejected entirely into the intergalactic medium.
To reach the numbers, the team used archival Hubble optical imaging to resolve stellar populations and reconstruct each galaxy's star-formation history, combined with data from the retired Spitzer Space Telescope and the Very Large Array and Australian Telescope Compact Array radio telescopes. As next steps, McQuinn plans to use the Roman Telescope to find even smaller galaxies and then observe them with Hubble and the James Webb Space Telescope. Telford, meanwhile, will use Hubble to zoom in on the individual massive stars that produce and eject the oxygen.
The image accompanying the study shows NGC 4449, an irregular dwarf galaxy about 12 million light-years from Earth in the constellation Canes Venatici — one of the 37 systems analyzed by the GLOW project.
Fontes:
- NASA Science — NASA’s Hubble Uncovers Case of Missing Oxygen in Nearby Dwarf Galaxies
- Rutgers University — Stars Make Oxygen for Small Galaxies. They Lose Most of It.
- Kristen B. W. McQuinn et al., “GLOW. II. A Census of Oxygen in Low-mass Galaxies”, The Astrophysical Journal 1011, 158 (2026)
Image credit: dwarf galaxy NGC 4449, imaged by the Hubble Space Telescope (NASA, ESA, Hubble Heritage–ESA/Hubble Collaboration, Alessandra Aloisi, STScI/ESA).
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