Astronomer Proposes Entirely New Category of Galaxy – ryan

Despite appearing “dead”—i.e., forming no new stars—some red galaxies may secretly be alive, quietly birthing small stars under our noses.

This is the conclusion of astronomy professor Charles Steinhardt of the University of Missouri, who has said these red galaxies could have played a much larger role in the history of the universe than we realized.

The new category of galaxies would be the third, falling outside the usual neat dichotomy of young, actively star-forming blue galaxies and their older, inactive red counterparts.

“The existence of these galaxies could mean that the universe has formed significantly more stars than previously estimated,” Steinhardt said in a statement on Wednesday.

“It supports the idea that the life cycle of galaxies is more complex than a simple progression from blue to red and dead,” he continued.

Traditionally, it has been understood that galaxies evolve either via gradual aging or by merging, during which the collisions can set off bursts of star formation.

Some of these freshly combined galaxies, however, seem to have just as abruptly stopped making new stars after an intense period of star formation.

It has been theorized that these “post-starburst” galaxies rapidly run out of energy after merging, bringing the new star formation to an end.

Steinhardt, however, has an alternate hypothesis: Some post-starburst galaxies may be, unbeknownst to us, slowly forming small, red stars over time.

If this is true, we may need to change how we categorize post-starburst galaxies, as some may be a different category of red star-forming galaxies in disguise.

“Red star-forming galaxies primarily produce low-mass stars, making them appear red despite ongoing star birth,” Steinhardt said.

“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,” he continued.

These issues, the astronomer explained, are problems that are “not explainable by aging or merging alone.”

Steinhardt added, “What we learned is that most of the stars we see today might have formed under different conditions than we previously believed.”

With this initial study complete, Steinhardt and his team are planning to investigate their hypothesis further—both by looking at post-starburst galaxies for evidence that some may fit in the new red star-forming category and by studying stars across the Milky Way.

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Reference

Steinhardt, C. L. (2025). Do Red Galaxies Form More Stars Than Blue Galaxies? The Astrophysical Journal982(2), 189.