New study challenges existing knowledge for why galaxies stop forming stars

A long-standing theory in astronomy is undergoing a serious reassessment. For decades, the consensus held that violent galaxy collisions triggered star formation shutdowns by fueling central black holes. A new simulation study led by researchers at Florida International University suggests this narrative is incomplete or even incorrect.

The team analyzed 11,724 simulated galaxies using the IllustrisTNG100 model. They found that most major mergers do not lead to the cessation of star formation. In fact, roughly 97 percent of major mergers in their dataset showed no association with galaxy quenching within a one-billion-year window. Instead of being the primary driver of death for a galaxy, mergers appear to be incidental events that occur without stopping the birth of new stars.

Data from the study indicates that quenching is far more tied to internal evolution. The mass of a galaxy's central black hole proved to be the most accurate predictor of whether a galaxy would stop forming stars. When black hole mass and total stellar mass were accounted for, the predictive power of merger history dropped to near zero. This suggests that galaxies fade through a slow, sustained loss of gas rather than a single dramatic event.

This finding points toward a quiet process where black holes maintain a steady output of energy that keeps surrounding gas too hot to form new stars. This continuous feedback loop seems more effective at quenching star formation than the chaotic energy release associated with a merger-induced quasar event. The research clarifies that while massive galaxies might experience more collisions, their shutdown is likely the result of internal maturation rather than external impacts.

By controlling for stellar and black hole mass, the researchers successfully separated genuine drivers of galactic change from simple correlations. This study provides a necessary framework for future observational surveys to track exactly how galaxies transition from active systems into the red, inactive states we observe across the cosmos today. The focus for astronomers now shifts from identifying violent culprits to understanding the long-term mechanics of gas supply.