Sources of Instability-Part Two

Sources of Instability (2) ...

We are increasingly aware that galaxies can interact strongly with each other, triggering rapid star formation.

Colliding Galaxies

The following image shows prolific star formation in the collision of two galaxies. The blue regions correspond to at least 1000 bright new star clusters that have been created in the collision.

We shall discuss such colliding galaxies and the role that they may play in new star formation more extensively in Chapter 24.

Shocks Generated by Massive Stars

The adjacent image shows a shell that has been expelled from a type of hot massive star called a Wolf-Rayet star. The star is generating shock waves in the nebula, and lies near a thick molecular cloud. We may expect that the ignition and subsequent strong solar winds from massive stars can destabilize nearby molecular clouds, thus triggering star formation.

Sequential Star Formation

There is strong evidence in some nebulae for waves of sequential star formation. We may envision this proceeding roughly as follows. An initial generation of stars is born due to a gravitational instability in part of a molecular cloud. In this set of initial stars some may be massive, producing a strong outpouring of radiation and stellar wind, and eventually becoming supernovae. The shocks generated by the radiation, wind, and supernova explosions then serve to compress gas in adjacent parts of the nebula, triggering collapse and a new wave of star formation. By such a process, we may envision a strong wave of star formation proceeding through a large molecular cloud, with older stars begetting newer stars. We shall discuss sequential star formation more extensively in Chapter 23.