globular cluster

History

In 1746, Jean-Dominique Maraldi first distinguished a globular cluster among other objects. Much later, in the early 20th century, astronomer Harlow Shapley used their distribution to realize that the Sun is far from the center of the Milky Way.

How it works

The stars in the cluster attract each other and revolve around a common center of mass. In the middle, they are packed more tightly and exchange gravitational kicks, changing their velocities and trajectories. This does not destroy the cluster, allowing it to live for billions of years.

History

In 1746, Jean-Dominique Maraldi first distinguished a globular cluster among other objects. Much later, in the early 20th century, astronomer Harlow Shapley used their distribution to realize that the Sun is far from the center of the Milky Way.

How it works

The stars in the cluster attract each other and revolve around a common center of mass. In the middle, they are packed more tightly and exchange gravitational kicks, changing their velocities and trajectories. This does not destroy the cluster, allowing it to live for billions of years.

History

The globular cluster M22 was first discovered by Johann A. Ihle in 1665. Systematic catalogs were compiled by Charles Messier and William Herschel in the 18th century. In the early 20th century, Harlow Shapley, studying the distribution of clusters, proved that the Solar System is located on the periphery of the Galaxy. Later, using Hertzsprung–Russell diagrams, the ages of clusters were determined, confirming cosmological time scales. In the 1990s, the Hubble Space Telescope revealed multiple stellar populations, complicating the picture of their formation.

How it works

The gravitational interaction of stars is described by the law of gravitation, and the statistical properties of the system follow from the virial theorem (twice the average kinetic energy equals the average potential energy). This allows measuring the total mass of the cluster from the velocity dispersion of stars. The tidal forces of the Galaxy strip away outer stars, and internal processes (evaporation of stars from the core and gravitational contraction) lead to slow evolution. Some clusters contain central intermediate-mass black holes or blue straggler stars—the result of mergers.

Open problems & fun facts

The origin of multiple chemical populations in clusters; The formation and growth mechanism of intermediate-mass black holes in their centers; Detailed dynamical history and interaction with dark matter in the halo

💡 Omega Centauri, the most massive globular cluster in the Milky Way, is possibly the remnant of a dwarf galaxy absorbed by our own.