Spiral Galaxies

Spiral Galaxies

The Milky Way is an example of a spiral galaxy. It is a galaxy in which several "arms" seem to unwind from a central region. Another example of a spiral galaxy is the Andromeda Galaxy, located in the constellation Andromeda.
The youngest stars and most of the gas and dust are located in the arms of a spiral galaxy. Since the hottest stars burn out quickly, whenever we see a hot star (which can be recognized by its blue colour), it must be relatively young. Colour photographs of galaxies show that the central regions are relatively yellow, indicating that older stars are dominant there, while the arms are relatively blue and therefore contain relatively young stars. [VH] {SR} {EB}