Plate Nº 83 · recorded November 9, 2026
Space & AstronomyReported finding
Dwarf Galaxies Keep Only a Tenth of the Oxygen Their Stars Make
A Hubble census of 37 nearby dwarf galaxies finds they retain on average only 11% of the oxygen their stars made, with supernova-driven winds ejecting the rest.
By Priya Raman4 min read801 words
In brief
- A Hubble census of 37 dwarf galaxies within 19.5 million light-years found they retain on average 11% of the oxygen their stars produced (range 4–25%).
- Galaxies more than 3.3 million light-years from a massive neighbor consistently retained less than 15% of their oxygen.
- Circumgalactic halos are estimated to hold 5–35% of the produced oxygen, meaning much may have escaped the galaxies entirely.
- Three cosmological simulations all overpredict how much oxygen dwarf galaxies retain compared with the observations.
- The study, GLOW II, was published in 2026 in the Astrophysical Journal (ApJ 1011, 158).
Gas-rich dwarf galaxies hold on to only about 11 percent of the oxygen their stars have produced over cosmic time, according to a Hubble Space Telescope census of 37 nearby systems published in the Astrophysical Journal. The remaining oxygen — roughly nine atoms in every ten — has been blasted out of these small galaxies altogether, almost certainly by the explosive deaths of massive stars.
"Oxygen is produced by stars, which are inside of galaxies," said Dr. Grace Telford, an astronomer at the University of Utah and a member of the team behind the findings. "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," she explained.
How do you count a galaxy's oxygen?
The census is the work of the Galaxies Losing Oxygen via Winds project, or GLOW, led by Dr. Kristen Wingfield McQuinn, mission head of the Science Operations Center for NASA's Nancy Grace Roman Space Telescope at the Space Telescope Science Institute and an astronomer at Rutgers University.
The team examined dwarf galaxies within roughly 19.5 million light-years of Earth, spanning stellar masses from about 3 million to 3 billion times that of the Sun.
The method proceeded in two steps. First, the researchers used Hubble observations of individual stars to reconstruct each galaxy's star formation history (a record of when, and in what quantity, stars formed over the galaxy's lifetime). That history told them how much oxygen the galaxy's stars should have manufactured in total. Second, they tallied how much oxygen is actually present today in each galaxy's gas, stars and dust.
The gap between the two numbers is large. The galaxies retained between 4 and 25 percent of the oxygen their stars produced, with a mean of about 11 percent. Nearly all of that retained oxygen sits in gas rather than in stars or dust. The rest, the authors conclude, was presumably expelled by supernova-driven outflows — a long-standing theoretical idea that this study, for the first time, puts on firm quantitative footing.
Does a galaxy's neighborhood matter?
Location appears to shape a dwarf galaxy's chemical fortune. Galaxies lying more than 3.3 million light-years from a massive neighbor consistently retained less than 15 percent of their oxygen. Those in denser surroundings, or within 3.3 million light-years of a big galaxy, showed more scatter and included most of the highest retention values in the sample.
The pattern suggests one of two possibilities: oxygen stripped by outflows may later be recycled back into these galaxies, or they may be pulling in gas already enriched with heavy elements by their larger neighbors. Distinguishing between the two will require further work.
Where does the missing oxygen go?
An obvious question follows. Is the lost oxygen still lurking in the halo of gas surrounding each galaxy — the circumgalactic medium, the diffuse envelope that envelops a galaxy's visible disk — or has it escaped the galaxy's gravitational grip entirely?
Earlier ultraviolet observations of a highly ionized form of oxygen (atoms stripped of several electrons, making them visible at ultraviolet wavelengths) account for only about 1 to 7 percent of what the galaxies produced. After correcting for other ionization states, the authors estimate the halos could hold somewhere between 5 and 35 percent. Even so, a large share of the missing oxygen may have traveled beyond the galaxies' gravitational reach altogether, enriching the intergalactic medium — the thin gas filling the space between galaxies.
The team also tested their numbers against three cosmological simulations (computer models that reproduce the growth of structure across the universe). All three reproduce the observed relation between galaxy mass and metal content, yet all predict that dwarfs keep more of their metals than the observations show.
A simple galaxy-evolution model matched the data best under three conditions: outflows carry away proportionally more mass from smaller galaxies; the outflowing gas is about twice as metal-rich as the galaxy's interstellar medium; and gas accretion onto these galaxies is suppressed by roughly 40 percent.
"So, it's really for practical reasons that we've chosen oxygen," Dr. McQuinn said. "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. It also helps us learn where and how much galaxies are enriching the space between galaxies."
The findings are published as McQuinn et al. 2026, GLOW. II. A Census of Oxygen in Low-mass Galaxies, ApJ 1011, 158.
via sci.news (Source)
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Senior reporter covering people, launches and day-to-day practice in general science news at SciBeat.
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Nearby plates
- Hubble Finds Dwarf Galaxies Are Losing Most of Their Oxygen
- Hubble Finds Missing Oxygen Across 37 Dwarf Galaxies
- Hubble Finds Stellar Winds Weaken Sharply in 29 Metal-Poor Stars
- Hubble finds stellar winds can suppress escaping ultraviolet light
- Early galaxies were already seeding the universe with heavy elements