Why do fainter stars make up most of a globular cluster’s mass?

Globular clusters are dominated by fainter stars in terms of total mass because, while the most luminous stars—such as red giants—contribute significantly to the cluster's visual brightness, they represent only a small fraction of the total stellar population.

In a typical globular cluster like M3, for example, approximately 90 percent of the visible light is emitted by stars at least twice as bright as the Sun. However, these bright, massive stars are relatively few in number. Conversely, more than 90 percent of the cluster’s total mass is comprised of numerous fainter, lower-mass stars that contribute very little to the overall luminosity of the system. Because these faint stars are so abundant, they collectively account for the vast majority of the cluster's mass, even though they are not the primary sources of its light.12