A new study examining the amounts of metals present in distant galaxies explains how they are slowly strangled to death over time. According to Dr. Yingjie Peng, an astronomer at the University of Cambridge in England, the new research offers insights into how galaxies form, evolve, and eventually die over billions of years.

How exactly is a galaxy strangled to death? When a galaxy is active, it is constantly forming new stars and using up the resources around it. In most cases, galaxies need a source of cold gas to form new stars. We know that when we cut off the air supply to a breathing organism, levels of oxygen decrease rapidly and carbon dioxide builds up in the lungs. But what if we examine this principle on a galactic scale?

As it turns out, galaxies are just as prone to choking as people are. When a galaxy’s cold gas source runs out, star formation will continue as long as there is enough residual fuel present. As an equilibrium state is reached in the absence of new gaseous star-forming reactions, what little gas that’s left is distributed between stars until it is all used up. The stars then burn out over their lifetimes, adding no new mass and giving off a wide range of gaseous metals.

Dr. Peng’s research aligned the changes in metal levels over time with the apparent life span of the galaxies in the study, and was surprised to find that the strangulation analogy was quite accurate. Dr. Peng says that the most likely cause of strangulation is overcrowding. Stars wind up strangling themselves as they consume all of the available cold gas, in a galactic tragedy of the commons.