Summary
A study of 37 nearby dwarf galaxies found they retain only a small fraction of the oxygen produced by their stars. The results suggest supernova-driven winds remove more oxygen from these low-mass galaxies than current simulations predict.
An analysis of 37 nearby dwarf galaxies found that they retain only a small fraction of the oxygen produced by their stars, NASA reports. The study, published in The Astrophysical Journal, suggests that winds powered by massive stars and supernova explosions carry more oxygen out of these low-mass galaxies than current simulations predict.
Oxygen is made inside stars and is relatively straightforward for astronomers to detect. Because it traces the distribution of other elements made by stars, measuring where oxygen resides can help researchers understand how galaxies evolve and enrich the space between them.
How the researchers traced oxygen
The Galaxies Losing Oxygen via Winds (GLOW) project examined galaxies whose masses fall in a range where simulations predict that an increasing share of their oxygen should be expelled. The 37 galaxies are close enough for Hubble to resolve individual stars, allowing researchers to study stellar populations and reconstruct star-formation histories from archival optical images.
The team combined those Hubble data with observations from NASA’s retired Spitzer Space Telescope and the ground-based Very Large Array and Australian Telescope Compact Array. Together, the observations were used to trace oxygen associated with stars, gas and dust in the galaxies and assess how much of the material produced by stars remained there.
The researchers found substantially less oxygen in the galaxies than simulations predict. Since that oxygen was produced by stars within the galaxies, the team interprets the shortfall as evidence that much of it was carried out by galactic winds. Energy from massive stars and supernovae can drive gas outward; the study indicates that this process is particularly effective at removing material from dwarf galaxies.
Why the missing oxygen matters
Galaxies do not evolve in isolation: material expelled from them can enrich the intergalactic medium, the space between galaxies. Establishing how much oxygen leaves dwarf galaxies helps scientists test models of both galaxy evolution and the distribution of elements across the universe.
Astronomers have previously found substantial oxygen loss from star-forming galaxies more like the Milky Way, with some of that material detected in the diffuse gas surrounding them. The GLOW work extends the investigation to lower-mass galaxies across a range of masses and environments. Its results point to stronger oxygen loss from these systems than current simulations anticipate.
The study’s key unresolved question is where the expelled oxygen ends up. Some may remain in the diffuse gas around dwarf galaxies, known as the circumgalactic medium; some may have travelled beyond their immediate surroundings. The NASA account says it is not yet clear which destination accounts for most of the missing oxygen.