![]() ![]() Typically the rate at which new stars are formed in pseudobulges is similar to the rate at which stars form in disk galaxies. Where they exist, these central spirals dominate the light of the bulge in which they reside. Giant spiral galaxies are typically 2–100 times the size of those spirals that exist in bulges. This structure often looks similar to a spiral galaxy, but is much smaller. Subsequent studies (using the Hubble Space Telescope) show that the bulges of many galaxies are not devoid of dust, but rather show a varied and complex structure. This contrasts greatly with elliptical galaxies. These bulges have stars that are not orbiting randomly, but rather orbit in an ordered fashion in the same plane as the stars in the outer disk. They are often referred to as pseudobulges or disky-bulges. Many bulges have properties more similar to those of the central regions of spiral galaxies than elliptical galaxies. Disk-like bulges Īstronomers refer to the distinctive spiral-like bulge of galaxies such as ESO 498-G5 as disc-type bulges, or pseudobulges. In contrast, about two thirds of galaxies in dense galaxy clusters (such as the Virgo Cluster) do possess a classical bulge, demonstrating the disruptive effect of their crowding. The bulgeless galaxy fraction of the Universe has remained roughly constant for at least the last 8 billion years. Indicating that they have never experienced a major merger. One study has suggested that about 80% of galaxies in the field lack a classical bulge, Following a major merger, gas clouds are more likely to convert into stars, due to shocks (see star formation). If either progenitor galaxy was gas-rich, the tidal forces can also cause inflows to the newly merged galaxy nucleus. Convulsing gravitational forces and torques disrupt the orbital paths of stars, resulting in the randomised bulge orbits. The distribution of light is described by a Sersic profile.Ĭlassical bulges are thought to be the result of collisions of smaller structures. Due to the lack of dust and gases, bulges tend to have almost no star formation. These stars are also in orbits that are essentially random compared to the plane of the galaxy, giving the bulge a distinct spherical form. These bulges are composed primarily of stars that are older, Population II stars, and hence have a reddish hue (see stellar evolution). The spiral structure ends at the onset of the bulge.īulges that have properties similar to those of elliptical galaxies are often called "classical bulges" due to their similarity to the historic view of bulges. ![]() An image of Messier 81, a galaxy with a classical bulge. ![]()
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