Galaxy Structure, Not Young Stars, Drives Molecular Gas in Messier 83

The life cycle of molecular gas in the barred spiral galaxy Messier 83 appears to be driven primarily by the galaxy’s large-scale structure and rotation, rather than by feedback from newborn stars, according to a new study.

Messier 83: The Southern Pinwheel Galaxy

Messier 83 is located approximately 15 million light-years away in the southern constellation Hydra.

Also known as the Southern Pinwheel Galaxy, M83, NGC 5236, LEDA 48082, and UGCA 366, it is about half the size of the Milky Way.

French astronomer Nicolas-Louis de Lacaille discovered Messier 83 on February 17, 1752. With an apparent magnitude of 7.5, it is one of the brightest spiral galaxies in the night sky. May is the best month to observe it with binoculars.

ALMA Maps Molecular Gas in M83

“Messier 83 is one of the brightest galaxies in the night sky, but this image taken with the Atacama Large Millimeter/submillimeter Array (ALMA) does not show what this galaxy looks like in the light we see,” Dr. Jin Koda of Stony Brook University and colleagues said in a statement.

“Instead, it depicts the light emitted by cold gas molecules, which are a component of star formation.”

Using ALMA, the astronomers mapped Messier 83’s molecular gas at a resolution of about 150 light-years.

The researchers compared two carbon monoxide emission lines. Their ratio tracks the density and temperature of the gas, revealing how molecular gas conditions vary throughout the galaxy.

Galaxy Rotation Shapes the Gas Cycle

The carbon monoxide ratio is very high at the center of Messier 83, decreases within the galaxy’s bar, rises again near the end of the bar, and then decreases in the outer disk, where spiral arms dominate.

Because this pattern is synchronized with the galaxy’s rotation, the researchers conclude that it is controlled primarily by the galaxy’s structure and dynamics.

Messier 83 is very similar to the Milky Way, and the findings are consistent with previous studies of our galaxy and other barred spiral galaxies.

“We are interested in molecular gas clouds because virtually all stars are born from collapse,” the scientists said.

“When a star forms, its surroundings heat up, condensing the gas and making it harder for more stars to form. This, combined with the dynamics of the galaxy that continuously stirs the gas, controls the growth of the galaxy.”

“With ALMA, we can map how the density and temperature of these gas clouds change at different locations within the galaxy, such as the central region, the spiral arms, or the space between them,” the researchers said.

“This helps us understand whether star formation occurs differently in different galactic environments.”

The team’s results were published in The Astrophysical Journal.

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Hitoshi Koda et al. 2026. Dynamically driven evolution of molecular gas in barred spiral galaxy M83 tracked by linear ratio variations of CO J = 2-1/1-0. Astrophysical Journal 986, 29. doi: 10.3847/1538-4357/add1dc