An arbitrary chosen OB star. These are hot, massive stars of
      spectral types O or B which form in loosely organized groups
      called OB associations. They are short lived, and thus don't
      move very far from where they were formed within their life.
      During their lifetime, they will emit copious amounts of
      ultraviolet radiation. This radiation rapidly ionizes the
      surrounding interstellar gas of the giant molecular cloud,
      forming an H II region.