X-ray view of Orion showing the Trapezium embedded cluster.
Embedded stellar clusters, or simply embedded clusters (EC), are open clusters that are still surrounded by their progenitor molecular cloud.[1]
They are often areas of active star formation, giving rise to stellar objects that have similar ages and compositions.[2]
Because of the dense material that surrounds the stars, they appear obscured in visible light but can be observed using other sections of the electromagnetic spectrum, such as the near-infrared and X-rays that can see through the cloud material.[3] In the Milky Way Galaxy, embedded clusters can mostly be found within the Galactic disk or near the Galactic Center where most of the star-formation activity is happening. [2]
The sizes of stellar objects born in embedded clusters may be distributed according to initial mass function, with many low-mass stars formed for every high-mass star. Nevertheless, the high-mass stars of temperature class O and B, which are significantly hotter and more luminous than the low-mass stars, have a disproportionate effect on their interstellar environment by ionizing the gas surrounding them creating H II regions. Many ultra-compact H II regions, the precursors to massive protostars, are associated with embedded clusters.[2]
Over time, radiation pressure and accretion of the remaining gas and dust surrounding the stellar objects, will disperse the molecular cloud and give rise to the better known open cluster.