The study of 37 nearby dwarf galaxies puts average retention at 11%, below model predictions, and researchers propose that galactic winds powered by massive stars and supernova explosions carry oxygen away.
Nearby dwarf galaxies—small galaxies with relatively few stars—hold far less of the oxygen their stars produced than computer simulations predict, researchers estimate. The GLOW researchers estimate that the 37 galaxies retain only 4–25% of the oxygen their stars produced, with a mean of 11%. Nearly all the oxygen they retain is in their gas. The finding challenges models of how effectively small galaxies keep the chemical elements made inside them.
NASA described the findings on 2 November, saying the research was published that Monday in The Astrophysical Journal. The Galaxies Losing Oxygen via Winds project, or GLOW, extends an earlier oxygen census to smaller galaxies. A 2014 study of star-forming galaxies similar to the Milky Way found that they had lost much of their oxygen, with some located in surrounding gas.
The team used archived Hubble Space Telescope images to distinguish individual stars and reconstruct when the galaxies formed stars and their chemical compositions. Combining those histories with measurements of gas mass and the abundance of heavy elements in gas between stars let the researchers compare estimated oxygen production with the oxygen still present.
The analysis also used data from NASA’s retired Spitzer Space Telescope and the ground-based Very Large Array and Australia Telescope Compact Array. Oxygen is useful for this accounting because it is relatively easy to detect and measure, and scientists understand its production in stars well, NASA said.
The galaxies were chosen because their masses fall in a range where theory predicts increasing oxygen loss through supernova explosions, and because they are close enough for Hubble to distinguish individual stars. Most known dwarf galaxies are too distant for this method, so the sample does not cover the full dwarf-galaxy population.
The storm flooded low-lying areas and brought down trees and electricity poles in Andhra Pradesh. The state’s disaster authority said no deaths or injuries had been reported.
Analysis
GLOW co-investigator Grace Telford, an assistant professor of physics and astronomy at the University of Utah, interprets the deficit as evidence that oxygen made inside the galaxies was later ejected. She said energy from massive stars and supernova explosions could drive material outward. The proposed winds explain the deficit; the study does not directly trace the missing oxygen’s escape.
Oxygen has been detected in the circumgalactic medium—the diffuse gas surrounding a galaxy outside its disk—but researchers still do not know whether most of the missing oxygen remains there or has escaped beyond those surroundings into the space between galaxies.
The team says simulations that model gas motion predict much higher oxygen retention, even though they reproduce the observed relationship between galaxy mass and its abundance of heavy elements. The researchers’ simpler modeling points to how much material winds carry and how rich those outflows are in heavy elements as controls on oxygen retention.
Telford is using Hubble for detailed observations of massive stars in nearby GLOW galaxies to characterize the stars that produce oxygen and help drive it outward.
GLOW principal investigator Kristen Wingfield McQuinn has an approved program to use NASA’s Nancy Grace Roman Space Telescope to find fainter, lower-mass nearby galaxies. Once those galaxies are identified, she hopes to use Hubble and NASA’s James Webb Space Telescope for deeper observations of their stars, allowing her team to reconstruct their star-formation histories.
3 min
Both licensed capsule strengths, 1mg and 0.25mg, were unavailable, the department said in the October 28 report. It issued guidance on alternatives, including unlicensed imports where available; the supplier hoped to reach patients by mid-December.
2 min
The warnings cover cardiovascular disease, breast cancer and dementia. The FDA did not convene advisers or present detailed evidence for its October 30 decision, but says it can provide the evidence later.
3 min
