What external forces cause open clusters to eventually disperse or 'evaporate'?
Answer
Tidal forces exerted by the galaxy and gravitational perturbations from passing molecular clouds
The binding force holding an open cluster together is inherently weak due to its low density and relative youth. As the cluster orbits the galactic center, it is constantly subjected to external gravitational stresses. The primary agents causing dissolution are the galaxy's massive tidal forces, which pull at the edges of the loose system, and gravitational perturbations caused by interactions with other large interstellar structures, such as passing molecular clouds. Over cosmic time, these external influences effectively strip the cluster's members away until the group disperses back into the general stellar population of the disk.
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