Where Does the Density Wave Theory Work?
For the spiral pattern to remain unchanged the density wave pattern must rotate like a solid disc. The spiral pattern must take the same amount of time for one revolution near its center as it does near its edge. 9;But actual velocitiy measures show that the stars, gas and dust, follow a totally different pattern of motion. The inner stars, gas, and dust gain laps on the outer stars, gas, and dust. As a consequence, the spiral density wave theory only works reasonably well at just one very limited distance from the galaxy center, where the density wave pattern is moving just a little slower than the orbital speed of the stars, gas, and dust. Close to the center of a spiral galaxy, the stars, gas, and dust, orbit much faster than theoretical spiral pattern speed, so the stars gas and dust rapidly pass through the density wave, and destroy the density concentration [instead of lingering in the density wave and adding their weight to the density concentration]. The fast motion of stars, g
