Hubble Finds Dwarf Galaxies Hold Only a Small Share of Their Oxygen

Dwarf galaxies appear to keep only a small fraction of the oxygen their stars make, and simulations have underestimated how much escapes. The result comes from the Galaxies Losing Oxygen via Winds (GLOW) project, which used Hubble to study 37 nearby dwarf galaxies. It is published in The Astrophysical Journal, and NASA announced it on November 2, 2026.

Dwarf galaxies are small systems with anywhere from a few thousand to hundreds of millions of stars. Theory says that in galaxies of the masses studied here, supernova explosions should blow a growing share of newly made oxygen out of the galaxy. The team found that the oxygen actually present falls well short of what simulations expect. Because stars made that oxygen inside the galaxies, the missing amount must have been driven out by energy from massive stars and supernovae. Grace Telford of the University of Utah, a co-investigator, put it this way: the oxygen “must have been ejected.”

The team chose oxygen for practical reasons. It is the most abundant element after hydrogen and helium, it is relatively easy to detect and measure, and how stars produce it is well understood. That makes it a handy tracer of heavy elements in general.

To do the accounting, the researchers used archival Hubble optical images to resolve individual stars, from which they worked out each galaxy’s star-formation history and composition. They combined these with data from the retired Spitzer Space Telescope and the ground-based Very Large Array and Australian Telescope Compact Array, to follow oxygen through stars, gas and dust. All 37 galaxies are close enough for Hubble to separate their stars, which is not true for most known dwarf galaxies.

A 2014 study found that Milky Way-like star-forming galaxies also lose a large fraction of their oxygen, some of it sitting in the diffuse gas halo around them called the circumgalactic medium. GLOW extends the question to low-mass galaxies across a range of masses and environments. Where the lost oxygen ends up is still open: it could be in that halo, or ejected from the galaxy’s surroundings entirely. The answer bears on how galaxies enrich the intergalactic medium, the space between galaxies. For more background, see our guide to galaxies.

What to watch next: Principal investigator Kristen Wingfield McQuinn has an approved program to use the Roman Space Telescope to find even fainter, lower-mass nearby galaxies, followed by deeper Hubble and Webb observations. Telford plans to use Hubble to study the massive stars in some GLOW targets in detail.