density wave

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A wave-like concentration of the density of interstellar material and stars that propagates through the disk of a spiral galaxy, giving rise to the spiral structure. The compression of the interstellar matter as it flows into the spiral arms causes star formation, and the bright, new-born stars outline the arms. The generation of the spiral wave may be aided by the existence of a central bar in the galaxy, or by tidal interaction with a companion galaxy.

Subjects: Astronomy and Astrophysics.

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