Astronomy Picture of the Day . W5: Pillars of Star Creation . ... JPL-Caltech , NASA Explanation: How do stars form? ... A likely reason for this is that the older stars in the center are actually triggering the formation of the younger edge stars. The triggered star formation occurs when hot outflowing gas compresses cooler gas into knots dense enough to gravitationally contract into stars. ... Publications with keywords: star formation . Publications with words: star formation . ...