A star forms from the gravitational contraction of a high density clump of cold, neutral gas and dust. The protostar gains in mass from the orbiting material which collects around it, called an accretion disk. Left to itself, the protostar will continue to grow until it gathers up all the available gas in its natal environment or disrupts this reservoir with outflows or jets the star produces as it evolves. However, only a few percent of all stars form in such regions. The overwhelming majority of low-mass stars form in the same clouds where massive stars form.
Massive stars ionize their natal environments with an enormous output of ionizing UV radiation.
This volume of hot, ionized plasma surrounding the new, massive stars is known as an H II region. Furthermore, planet formation appears to occur in the last remnants of accretion disks. Destruction of this protoplanetary material would stop a planetary system from forming around these stars. This has strong implications on the likelihood of stars developing planetary systems. By studying the distribution of young stars with circumstellar disks in H II regions, we may get a better understanding of the effect of massive stars on the formation of low-mass stars and planetary systems.