 Some of these collapsing stars can be particularly massive , and can emit large quantities of ionizing ultraviolet radiation . An example of this is seen with the Trapezium cluster . Over time the ultraviolet light from the massive stars at the center of the nebula will push away the surrounding gas and dust in a process called photo evaporation . This process is responsible for creating the interior cavity of the nebula , allowing the stars at the core to be viewed from Earth . The largest of these stars have short life spans and will evolve to become supernovae . 
