Astronomy
The Formation and Evolution of Globular Clusters
Quick fact
The globular cluster Messier 80 is about 12 billion years old, meaning its stars formed when the universe was only about a billion years old.
Why this is interesting
You've likely seen images of glittering clusters of stars, but did you know that some of these spheres contain some of the oldest stars in the universe—nearly as old as the universe itself? How can such ancient, dense groups of stars form and then survive for over 13 billion years?
Read the full explanation
Understanding The Formation and Evolution of Globular Clusters
Imagine a city where hundreds of thousands of people are packed into a tight area, all born at the same time. That's a globular cluster: a spherical collection of stars bound by gravity, each containing anywhere from 100,000 to a million stars. These clusters are ancient, formed from giant clouds of gas and dust that collapsed under their own weight early in the universe's history. In contrast to open clusters, which are looser and younger, globular clusters are dense, spherically symmetric, and typically orbit the halo of a galaxy.
A deeper explanation
The story of a globular cluster begins with a massive molecular cloud—a cold, dense region of gas and dust. A disturbance, such as a shockwave from a supernova or collision, triggers gravitational collapse. This collapse causes the cloud to fragment into numerous smaller cores, each of which becomes a star. Because this happens nearly simultaneously, all stars in a cluster are born around the same time, making them a single stellar population. After the initial burst of star formation, the remaining gas is blown away by radiation from massive young stars, leaving a bound cluster of stars. Over billions of years, the cluster evolves dynamically. Stars interact gravitationally, with some being ejected (a process called evaporation), while the cluster slowly contracts and becomes more concentrated. The most massive stars evolve first, undergoing supernovae, while lower-mass stars become red giants and eventually white dwarfs. By studying the colors and luminosities of stars in a globular cluster (on a Hertzsprung-Russell diagram), astronomers can precisely determine the cluster's age—these clusters are found to be around 12-13 billion years old, making them touchstones for understanding the early universe and the assembly of galaxies.