If there is too much available matter, it will form too many stars at an accelerated rate, leaving the formation of intense red stars. The author states that in galactic terms, red stars means that the galaxy is old and "dead."
He goes on to discuss that the inner parts of elliptical galaxies rotate and move at much higher velocities than their further out counterparts.
This can confirmed via Keplers second law:
The closer an orbiting object is to its center would need to have a higher velocity to cover the same area an object orbiting at further distances would.
The spiral arms on a galaxy are thought to be "star factories." The gas clouds in the spiral arms moves faster than that orbiting planets/debris fields. When they collide this process compresses the gasses and influences the formation of new stars.
In the spiral arms of galaxies, there are brighter, larger stars that are blue. These stars are short lived compared to that of the long lived, smaller red stars. When astronomers take images of the galaxies, they are observing much of these larger, blue stars. These larger stars block out the view of a lot of matter in the arms of the galaxy giving the impression of "pinwheel galaxies."
Only by taking long exposure images, astronomers can see all the extra matter in the gaps in the arms of galaxies.
This is a picture of a whirlpool galaxy, NGC 5194, and is one of the brightest galaxies we can observe. The image was taken from Hubble and Kitt Peak National Observatory.
Source: http://www.space.com/30982-there-is-a-trick-to-making-a-spiral-galaxy.html
3 points. We'll discuss a lot about this in the coming weeks. Why old galaxies are red, why colliding gas clouds would create stars...
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