This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in the Southern Pinwheel Galaxy.īars are thought to be temporary phenomena in the lives of spiral galaxies the bar structures decay over time, transforming galaxies from barred spirals to more "regular" spiral patterns. The bar structure is believed to act as a type of stellar nursery, channeling gas inwards from the spiral arms through orbital resonance, fueling star birth in the vicinity of its center. This effect builds over time to stars orbiting farther out, which creates a self-perpetuating bar structure. The creation of the bar is generally thought to be the result of a density wave radiating from the center of the galaxy whose effects reshape the orbits of the inner stars. īarred galaxies are apparently predominant, with surveys showing that up to two-thirds of all spiral galaxies contain a bar. Among other types in Hubble's classifications for the galaxies are the spiral galaxy, elliptical galaxy and irregular galaxy.įurther information: Density wave theory § Galactic spiral arms Barred spiral galaxy IC 5201, located more than 40 million light-years from Earth. A new type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Clouds, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. SBb-type galaxies lie in between the two. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. Įdwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy. Bars are found in about two thirds of all spiral galaxies, and generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. Spiral galaxy with a central bar-shaped structure composed of stars NGC 1300, viewed nearly face-on Hubble Space Telescope imageĪ barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars.
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