HUBBLE SURVEY FINDS DWARF GALAXIES LOSE MOST OF THEIR OXYGEN

A survey using the Hubble Space Telescope's Cosmic Origins Spectrograph has found that dwarf galaxies lose almost all the oxygen they produce. The research, published in The Astrophysical Journal, examined 37 nearby dwarf galaxies in the GLOW survey — Galaxies Losing Oxygen via Winds. On average, each galaxy retained only about 11 per cent of the oxygen it manufactured, and in some cases up to 96 per cent was lost. Stellar winds and supernova explosions carried the oxygen into the surrounding space and far beyond it. The findings suggest computer models used to predict this process were inaccurate by a factor of two to three.

Oxygen acts as a tracer for astronomers, indicating how much stellar processing a galaxy has undergone. Massive stars fuse oxygen in their cores and scatter it into space when they explode as supernovae. The amount of oxygen a galaxy retains determines its metallicity, a term for elements heavier than hydrogen and helium. The mass-metallicity relation shows that more massive galaxies tend to be richer in metals. Dwarf galaxies have formed stars and produced heavy elements for billions of years, but have remained low in metallicity — a long-standing puzzle for astronomers.

Researchers measured the escaping oxygen by studying light passing through each galaxy's surrounding halo of gas, rather than observing the galaxy directly. The GLOW survey is described as the first systematic effort to measure how much oxygen low-mass galaxies lose and trace where it goes. Dwarf galaxies are the most common type of galaxy in the universe, so the findings carry implications for models of galactic chemical evolution. The results explain why dwarf galaxies, which formed stars for billions of years, appear chemically primitive.