Star formation caused by density waves in the galactic disk of the galaxy.

The following hypotheses exist for star formation caused by density waves:

As gas clouds move into the density wave, the local mass density increases.

The spiral arms are thought to be areas of high-density matter, or "density waves".

The most intriguing properties of density waves are their dynamics.

In addition, this encounter also amplified the density waves in the spiral arms of M101.

The density waves and the bending waves were not a surprise.

Forty such "density waves" were observed in the A ring, one of the broadest.

Since star formation does not happen immediately, the stars are slightly behind the density waves.

These stars have relatively short lifetimes, however, and expire before fully leaving the density wave.