Orion is conspicuous in the sky because of its hot blue luminous stars, but infrared exposures reveal thousands of fainter low-mass stars.
Star formation can trigger further star formation in adjacent regions of an interstellar cloud.
The formation of a young cluster, with its hot blue stars prominent, can affect adjacent gas in two ways. The pressure of ultraviolet radiation from the hot stars can compress adjacent gas, triggering new star formation. Within a few million years after formation, the most massive stars explode as supernovas. The shock wave from these exploding stars can trigger further star formation. Such a process is called sequential star formation .