Hubble Reveals Missing Oxygen in Dwarf Galaxies
Oxygen is produced by stars, which are inside of galaxies,
University of Utah astrophysicist O. Grace Telford said.
Astronomers using the Hubble Space Telescope have discovered that 37 nearby dwarf galaxies are missing most of the oxygen their stars produced over their lifetimes. Researchers found that these small systems, which hold anywhere from a few thousand to hundreds of millions of stars, have retained only a small fraction of the heavy element.
The cosmic inventory was conducted as part of the Galaxies Losing Oxygen via Winds project, a research effort funded by NASA and the National Science Foundation. To track the missing material, the team combined new and archival observations from Hubble, the retired Spitzer Space Telescope, and ground-based radio facilities including the Very Large Array and the Australian Telescope Compact Array.
Where's the oxygen? After researchers studied nearby dwarf galaxies, they realized much of the oxygen they expected to see was missing. Galactic winds from supernova explosions are apparently more effective at removing oxygen than current models predict: https://t.co/h9Wns2NvY6 pic.twitter.com/Q5fjsH0lBE
The missing oxygen likely escaped the gravitational pull of these low-mass galaxies through energetic stellar winds and core-collapse supernovae. According to the research published in The Astrophysical Journal, dwarf galaxies hold a mean of just 11 percent of the oxygen generated by their stellar populations, with individual retention rates ranging from 4 percent to 25 percent.
Weak gravity limits oxygen retention in low-mass galaxies
Most oxygen forms during the explosive deaths of massive stars, known as core-collapse supernovae, while lower-mass stellar remnants contribute a very small fraction. Because oxygen is the universe’s third most abundant element and its production is well understood, astronomers use it as a primary tracer for how heavy elements circulate through galaxies.
Low-mass galaxies struggle to retain this gas because their gravitational fields are much weaker than those of large spirals like the Milky Way. When massive stars die and detonate, their explosions drive oxygen-rich gas outward into the circumgalactic medium and out into the wider intergalactic medium. While massive galaxies retain much higher proportions of heavy elements, the GLOW project demonstrates that dwarf galaxies purge their supplies far more efficiently.
Location also influences how much oxygen a dwarf galaxy manages to keep. Systems situated more than 3.3 million light-years away from a massive neighbor consistently retained less than 15 percent of their oxygen. Conversely, dwarf galaxies in denser environments or close to large neighbors showed more varied retention rates, pointing to possible gas recycling or accretion from nearby systems.
Tracking the Escaped Gas
Where the expelled oxygen eventually goes remains an open question in galactic evolution. Previous ultraviolet observations of ionized oxygen found only 1 to 7 percent of the expected total residing in the hot gas halos surrounding dwarf galaxies. Even after accounting for cooler gas phases, circumgalactic halos likely hold at most about one-third of the oxygen produced by their stars.
The disparity between predictions and observations highlights gaps in current astrophysical models. The GLOW project team compared their empirical measurements against three cosmological simulations and found that the models underpredict how much oxygen low-mass galaxies actually lose. This discrepancy implies that researchers do not yet fully understand the feedback mechanisms between massive stars and their host galaxies.
Future investigations will utilize Hubble alongside upcoming facilities like the James Webb Space Telescope and the Nancy Grace Roman Space Telescope to examine star-formation histories in greater detail. Kristen W. McQuinn, GLOW principal investigator at the Space Telescope Science Institute, noted that tracking these elements clarifies how galaxies enrich the intergalactic medium over cosmic time.
How much oxygen do larger galaxies retain
How much oxygen do larger galaxies retain compared to dwarf galaxies?
While dwarf galaxies retain an average of roughly 11 percent of their stellar oxygen, much larger galaxies like the Milky Way hold significantly higher concentrations, maintaining roughly three to four times the proportion found in low-mass systems.
Hubble studied 37 nearby dwarf galaxies and found far less oxygen than simulations predict. Researchers say supernova-driven winds blew it out into intergalactic space. Footage is illustrative. Source: NASA / ApJ Did you expect that? 👇 #Hubble #Astronomy pic.twitter.com/qS0r7XwQIo
What tools did astronomers use to calculate star formation histories?
Researchers used high-resolution imaging from the Hubble Space Telescope to pick out individual stars within the nearby dwarf galaxies. This detailed level of resolution allowed the team to reconstruct past star birth and calculate how much oxygen those stars should have generated.
Where is the rest of the oxygen believed to be located?
Scientists suspect the missing oxygen was driven into the gaseous halos surrounding the galaxies and out into the intergalactic medium. However, current surveys of surrounding gas halos account for at most about one-third of the total oxygen missing from the galaxies.
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