Barred spiral galaxy

A barred spiral galaxy is a spiral galaxy with a band of bright stars emerging from the center and running across the middle of the galaxy. Spiral arms appear to emerge from the ends of the "bar" in these galaxies, whereas they appear to emerge directly from the core in ordinary spiral galaxies.

Related Topics:
Spiral galaxy - Star - Galaxy - Spiral arm

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Edwin Hubble classified these types of spiral galaxies as "SB" ("Spiral", "Barred"), and arranged them into three sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb type galaxies lie in between. A fourth type, SBm, was subsequently created to describe dwarf barred spirals, such as the Magellanic Cloud galaxies, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures.

Related Topics:
Edwin Hubble - Classified - Magellanic Cloud galaxies - Irregular galaxies

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Barred spiral galaxies are relatively common, with surveys showing that up to two-thirds of all spiral galaxies contain a bar. The current hypothesis is that the bar structure acts as a type of stellar nursery, fueling star birth at their centers. The bar is thought to act as a mechanism that channels gas inwards from the spiral arms through orbital resonance, in effect funneling the flow to create new stars. This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in Messier 83.

Related Topics:
Hypothesis - Stellar nursery - Star birth - Gas - Active galactic nuclei - Messier 83

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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. This effect builds over time to stars orbiting further out, which creates a self-perpetuating bar structure. Another possible culprit in bar creation are tidal disruptions between galaxies.

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Bars are thought to be a temporary phenomenon in the life of spiral galaxies, the bar structure decaying over time, transforming the galaxy from a barred spiral to a "regular" spiral pattern. Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Barred spiral galaxies with high mass accumulated in their center tend to have short, stubby barshttp://www.govertschilling.nl/artikelen/archief/2002/0204/020401_st.htm. Since so many spiral galaxies have a bar structure, it is likely that it is a reoccurring phenomenon in spiral galaxy development.

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In 2005, observations by the Spitzer Space Telescope backed up previously collected evidence that suggested the Milky Way is a barred spiral galaxy. Observations by radio telescopes had for years suggested our galaxy to be barred, but Spitzer's vision in the infrared region of the spectrum has provided a more definite calculation.

Related Topics:
2005 - Spitzer Space Telescope - Milky Way - Radio telescope - Year - Spitzer's vision - Infrared - Region of the spectrum - Calculation

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