Why do stars in a star cluster have a common origin?
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.
Stars in a star cluster share a common origin because they are born together within the same molecular cloud.12
These clouds are vast, clumpy regions of gas and dust where star formation occurs in dense areas known as cloud cores. Because these stars form from the same parent material in a localized region, they are physically related. The specific outcome of this process—whether the stars form a bound cluster or an unbound association—depends on the efficiency of star formation; if a sufficient percentage of the cloud core's mass is converted into stars, the resulting group remains gravitationally bound to one another.341
Once formed, these stars remain together as a cluster, held by their mutual gravitational attraction. This shared birth environment is why members of a cluster often exhibit similar characteristics, such as age and chemical composition, reflecting the conditions of the molecular cloud from which they emerged.156