Galaxies should lose their spiral shape over millions of years (Talk.Origins)
- Stars closer to the center of a spiral galaxy orbit the galaxy faster than stars farther away. Over many millions of years, the difference in orbital rates should wind the spiral tighter and tighter. We do not see any evidence for this in galaxies of different ages.
- Corliss, William R., 1988. Why do spiral galaxies stay that way? or do they? Science Frontiers Online 55 (Jan-Feb).
CreationWiki response: (Talk.Origins quotes in blue)
1. Spiral arms are density waves, which, like sound in air, travel through the galaxy's disk, causing a piling-up of stars and gas at the crests of the waves. In some galaxies, the central bulge reflects the wave, giving rise to a giant standing spiral wave with a uniform rotation rate and a lifetime of about one or two billion years.
First of all this is a theory not a proven fact. Furthermore, it does not come from first principles, but is simply the latest in a series of theories designed to save the long age theoretical system from reality.
While, when properly tuned, the Density Wave Theory can produce the basic spiral shape, Hubble images of Whirlpool Galaxy and others show that they are too tightly wound near the core to be explained by the Density Wave Theory. On the other hand the Windup Model predicted this tight winding perfectly.
The causes of the density waves are still not known, but there are many possibilities. Tidal effects from a neighboring galaxy probably cause some of them.
This is just one of several problems with the Density Wave Theory.
The spiral pattern is energetically favorable. Spiral configurations develop spontaneously in computer simulations based on gravitational dynamics (Carlberg et al. 1999).
This is gravitational dynamics with the proper assumptions made. The Windup Model also produces spontaneous spiral configurations in computer simulations based on gravitational dynamics, but with fewer assumptions. It also produces the observed spiral structures from first principles, and in perfect detail.