RCW120

RCW120 is an expanding bubble of ionized gas about ten light-years across, causing the surrounding material to collapse into dense clumps, creating new stars.

A hot, massive star in its centre is emitting huge amounts of ultraviolet radiation, which ionizes the surrounding gas, stripping the electrons from hydrogen atoms and producing the characteristic red glow of so-called H-alpha emission.

As this ionized region expands into space, the associated shock wave sweeps up a layer of the surrounding cold interstellar gas and cosmic dust. This layer becomes unstable and collapses under its own gravity into dense clumps, forming cold, dense clouds of hydrogen where new stars are born. However, as the clouds are still very cold, with temperatures of around -250 C, their faint heat glow can only be seen at submillimetre wavelengths.