An Etymological Dictionary of Astronomy and Astrophysics

A → galaxy bulge that appears protruding from the disk plane when seen at an appropriate → inclination. Classical bulges are somewhat → spheroidal, featureless (no → spiral arms, → bars, → rings, etc.), contain mostly → old stars (not much dust or star-forming regions), and are kinematically hot, i.e. dynamically supported by the → velocity dispersion of their stars. Their → surface brightness profile follows the → de Vaucouleurs law. Currently, they are thought to form through → gravitational collapse or → mergers
in violent events, inducing a fast → burst of star formation if gas is available. An example is the → Sombrero galaxy bulge (D. A. Gadotti, 2012, astro-ph/1208.2295).

See also: → classical; → bulge.