How do tidal forces from the Milky Way disrupt open clusters?
Most of the brightest stars are older yellow stars, but a few young blue stars are also visible. This picture is a composite of three images taken by the Hubble Space Telescope.
Open clusters are characterized by their relatively small total mass and loose structure, which makes them highly susceptible to the gravitational environment of the Milky Way. Unlike massive globular clusters, which are robust enough to withstand galactic influences, open clusters lack the strong gravitational binding necessary to resist disruptive tidal forces.12
These tidal forces act upon the clusters as they orbit within the Galaxy, leading to a gradual dispersal of their member stars. Because of this instability, most open clusters are short-lived; only about half of those within 3,000 light-years of the Sun can survive these tidal effects for more than 200 million years, and only a very small percentage persist for as long as 1 billion years. Consequently, open clusters are generally young objects that eventually fade away as their stars are scattered into the general galactic population.21