Bulges that have properties similar to elliptical galaxies are often called classical bulges due to their similarity to the historic view of bulges. These bulges are composed primarily of stars that are older population II stars, and hence have a reddish hue (see stellar evolution). These stars are also in orbits that are essentially random compared to the plane of the galaxy, giving the bulge a distinct spherical form. Due to the lack of dust and gasses, bulges tend to have almost no star formation. The distribution of light is described by de Vaucouleurs' law.
Classical bulges are thought to be the result of collisions of smaller structures. This disrupts the path of the stars, resulting in the randomness of bulge orbits. Also during the merger, gas clouds are more likely to be converted into stars, due to the shocks from the mergers (see Star Formation).
Read more about this topic: Bulge (astronomy)
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