How do massive young star clusters form?
|A Hubble image of the Arches star cluster. Astronomers compared young massive|
gas clouds in the galaxy with the Arches and other more developed star clusters
to model how these clusters developed [Credit: NASA/Hubble Space Telescope]
The mechanism by which young massive star clusters form is not well understood. The two most popular scenarios are formation in a bound, centrally condensed natal cloud which subsequent evolves and expels the remaining gas (the "monolithic model"), or formation in smaller stellar groups that hierarchically come together to become centrally condensed (the "hierarchical model"). CfA astronomer Daniel Walker and his colleagues tested a refinement of these two scenarios in which the cluster forms in the "conveyor-belt" mode (both the cloud and the star cluster shrink together), the "in-situ" mode (the dense gas experiences little or no contraction), or the "popping" mode (the gas is at higher density than the young stars but then expands to lower density).
The scientists compiled a sample of ten young massive gas clouds and compared them to six existing young massive clusters in the central region of our galaxy, and then examined their properties using the submillimeter dust emission which measured the masses and temperatures. They found that the "conveyor-belt" mode of formation was consistently more probable, although in some instances the "in situ" mode was plausible. (The "popping" mode was never preferred.) The results suggest that young massive star clusters form as clouds gradually contract and accumulate more mass in their central regions along with concurrent star formation.
Source: Harvard-Smithsonian Center for Astrophysics [April 08, 2016]