Researchers using NASA’s Hubble Space Telescope have discovered that most nearby dwarf galaxies are missing the majority of the oxygen produced by their stars, according to findings published this week in The Astrophysical Journal. The study, which examined 37 dwarf galaxies within roughly 19.5 million light-years of Earth, found that these small galaxies retain only a small fraction of the oxygen generated by stellar processes.
The international team behind the research determined that, on average, the galaxies studied kept just 11 percent of the oxygen their stars created over time. The most efficient galaxies managed to hold onto about a quarter of their oxygen, while the least efficient retained as little as 4 percent. The findings suggest that the rest of the oxygen has either escaped into the gas halos surrounding the galaxies or been expelled entirely into intergalactic space.
The research is part of the Galaxies Losing Oxygen via Winds (GLOW) project, a collaboration funded by NASA and the National Science Foundation. The team combined data from the Hubble Space Telescope with observations from NASA’s retired Spitzer Space Telescope and ground-based facilities, including the Very Large Array and the Australian Telescope Compact Array, to measure the oxygen content in the stars, gas, and dust of each galaxy.
“Oxygen is produced by stars, which are inside of galaxies,” said Dr. Grace Telford, an astronomer at the University of Utah, as quoted by Sci.News. To estimate how much oxygen should be present, the researchers reconstructed the star formation history of each galaxy using Hubble’s observations of individual stars. They then tallied the actual oxygen content in the galaxies’ gas, stars, and dust.
Most of the oxygen was found in the gas component of each galaxy, rather than in the stars themselves. However, the total amount fell far short of what models predicted based on the galaxies’ star formation histories. According to NASA, while previous studies have shown that galaxies can lose heavy elements like oxygen, the new findings highlight just how inefficient dwarf galaxies are at retaining these crucial elements.
The fate of the missing oxygen remains uncertain. Some of it may reside in the circumgalactic medium—the diffuse halo of gas surrounding each galaxy—but the study notes that it is still unclear whether most has escaped entirely from the galaxies’ environments. The research also found that dwarf galaxies located in denser regions or near larger galaxies showed more variation in their oxygen retention, possibly due to recycling of oxygen-rich gas or accretion from neighboring galaxies.
Dwarf galaxies are much smaller than galaxies like the Milky Way, containing anywhere from a few thousand to hundreds of millions of stars. Their relatively shallow gravitational wells make them more susceptible to losing gas and heavy elements through powerful galactic winds, often driven by supernova explosions. This process is believed to be far more effective in dwarf galaxies than in their larger counterparts, which typically retain three to four times as much oxygen as the dwarfs studied.
The GLOW project aims to better understand how gas and heavy elements move between low-mass galaxies, their surrounding halos, and the vast space between galaxies. The findings have implications for models of galaxy evolution and the chemical enrichment of the universe.
Why it matters
The discovery that dwarf galaxies lose most of their oxygen challenges existing models of how galaxies evolve and how elements are distributed across the cosmos. According to NASA and the GLOW research team, these results suggest that small galaxies play a significant role in enriching intergalactic space with oxygen and other heavy elements, which are essential for the formation of planets and, ultimately, life.
The study’s use of multiple observatories—including Hubble, Spitzer, and major radio telescope arrays—demonstrates the importance of combining data from different wavelengths to track the movement of elements within and beyond galaxies. This approach has provided new insights into the efficiency of galactic winds in removing oxygen from low-mass galaxies, a process that may have shaped the chemical makeup of the universe over billions of years.
As the GLOW project continues, astronomers will seek to pinpoint the final destinations of the missing oxygen and refine models of galaxy evolution. The findings also underscore the need for future space telescopes and observatories to probe the faint halos and intergalactic regions where much of the universe’s oxygen may reside.
The image accompanying this article is an AI-generated illustrative depiction inspired by the actual scene of the event.
