Show-Me State Times

The cosmos, unlike most systems, lacks a guidebook. However, University of Missouri Assistant Professor Charles Steinhardt posits that humanity might be interpreting existing cosmic rules incorrectly, or perhaps the universe is governed by a set of rules not fully understood.

Galaxies have traditionally been classified into two groups: blue, indicating youth and active star formation, and red, representing older, star-formation-inactive galaxies. Steinhardt presents a novel third group: red star-forming galaxies. These galaxies defy the conventional categories, residing between blue and red classifications.

“Red star-forming galaxies primarily produce low-mass stars, making them appear red despite ongoing star birth,” Steinhardt explained. “This theory was developed to address inconsistencies with the traditional observed ratios of black hole mass to stellar mass and the differing initial mass functions in blue and red galaxies — two problems not explainable by aging or merging alone. However, what we learned is that most of the stars we see today might have formed under different conditions than we previously believed.”

Steinhardt suggests these galaxies could have significantly impacted the universe's evolution. He speculates this new understanding might require reassessment of galaxy evolution and star formation measurement methods.

“The existence of these galaxies could mean that the universe has formed significantly more stars than previously estimated,” Steinhardt said. “It supports the idea that the life cycle of galaxies is more complex than a simple progression from blue to red and dead.”

Traditionally, astronomers have struggled to explain post-starburst galaxies—galaxies that abruptly cease star formation following an intense period of activity, typically believed to arise via galaxy mergers inducing star-forming bursts. However, Steinhardt proposes an alternative theory, suggesting some such galaxies gradually formed small red stars instead of experiencing sudden star formation spurts. This perspective could redefine post-starburst galaxies as belonging to the novel red star-forming category.

Steinhardt, along with his students at Mizzou’s Department of Physics, plans to perform further tests. Junior Mathieux Harper, along with undergraduate students, will gather evidence supporting the notion that some post-starburst galaxies fit the newly proposed category. Simultaneously, sophomores Carter Meyerhoff and Zach Borowiak will harness the European Space Agency’s Gaia satellite data to analyze over two billion stars within the Milky Way.

“Do Red Galaxies Form More Stars Than Blue Galaxies?” detailing these findings, appeared in the Astrophysical Journal.