Embedded cluster

[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.

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.