By Eric Stann
Aug. 11, 2026
Contact: Eric Stann, StannE@missouri.edu
University of Missouri researchers have uncovered evidence that challenges one of astronomy’s most trusted assumptions, a breakthrough that could reshape how scientists measure galaxies and reconstruct the history of the universe.
For decades, astronomers have estimated the number of small, unseen stars in distant galaxies using a mathematical rule that assumed stars form in roughly the same proportions everywhere in the universe.
Scientists from Mizzou’s College of Arts and Science found that isn’t always the case. Instead, the ratio of large and small stars appears to depend on the environment in which they formed.
The discovery could help astronomers make more accurate estimates of galaxy mass, age and evolution. The findings may also help explain why some galaxies observed by NASA's James Webb Space Telescope appear more massive than expected because those galaxies may simply have formed stars differently than astronomers once assumed.
“One of astronomy’s basic assumptions may be oversimplified,” Charles Steinhardt, an astronomy professor and co-author of the study, said. “Other galaxies weren’t breaking the laws of physics — we were measuring them with the wrong yardstick.”
That yardstick is the initial mass function, or IMF. Because astronomers cannot directly observe most of the smallest, faintest stars in distant galaxies, they use the IMF to estimate how many should exist based on the brighter stars they can see. That approach has been a cornerstone of modern astronomy for more than 50 years.
To test their idea, Mizzou researchers analyzed data from the European Space Agency’s Gaia mission, which has mapped nearly 2 billion stars in the Milky Way. They focused on star clusters, or groups of stars that formed together under similar conditions. Comparing those clusters allowed the researchers to test whether stars form in the same proportions everywhere.
If the IMF were truly universal, every cluster would contain a similar mix of stars. Instead, the researchers found significant differences from cluster to cluster, suggesting local conditions influence the types of stars that form.
Rather than discarding the IMF, the researchers propose refining it by accounting for the different types of environments where stars form.
“The pattern we found is surprisingly clean,” Carter Meyerhoff, an undergraduate researcher and co-author of the study, said. “Instead of applying the same model to every galaxy, astronomers could account for the conditions under which stars formed and select the IMF that best matches that environment.”
The findings point to a more flexible framework for understanding star formation and interpreting observations of distant galaxies.
“We’ve found that the universe is more complicated than we assumed,” Steinhardt said. “But we’re also getting closer to measuring it correctly.”
The study, “Direct evidence for stellar initial mass function variation in the Milky Way,” was published in The Astrophysical Journal Letters. Alexander Luening at University of Rochester also contributed to the study.
