Barred Spiral galaxy

A barred spiral galaxy , is a Spiral galaxy of which the arm emergent step of the center of the galaxy, but of a band of star S crossing this center.
The arms spirals seem to emerge from the ends of the bar of these galaxies, considering which they appear to emerge directly from the core of an ordinary spiral galaxy.

Edwin Hubble classified these types of spiral galaxies like SB (" Spirale" , " Barrée") in its Hubble sequence. It indexed them in three subcategories, themselves based on the form and the way in which the arms of the spiral are laid out. The SBa types present arms closely dependant between them. Contrary, the SBc types present very detached arms far from thus dependant. Lastly, the SBb types range between the two.
A fourth type, SBm, are then created to describe the irregular barred spirals, like those of the Nuages of Magellan, which were formerly classified like irregular galaxies.

In 2005, the observations of the Space telescope Spitzer support the evidence collected previously and which suggests that the Milky Way is a spiral galaxy barrée.
The observations made by the Radiotélescope S suggested during years that our galaxy was a barred spiral galaxy but the images of Spitzer in the areas Infrarouge S of the spectrum, provided more precise elements.

Bars

The barred spiral galaxies are comparatively numerous. Studies showed that two galaxies out of three contain a bar. Various assumptions exist concerning these bars.

The current assumption concerning these bars says that their structure acts like a kind of " pouponnière stellaire" , nourishing young stars. It is thought that the bar acts as a mechanism which feeds in Gaz the internal chains of the spiral through a orbital Résonance, by draining the Flux (of gas) to create new stars. This theory explains why many barred spiral galaxies have a active galactic Noyau, like that of the southern Galaxie " Pinwheel".

It is thought that the creation of the bar is the result of a " vagueness of densité" radiant of the center of the galaxy and of which the effects reform the Orbite S of internal stars. This effect implies that with time, of stars orbit outside, which increases the bar.

One also thinks that the bars are a temporary phenomenon in the life of the spiral galaxies, the structure of the bar declining with the wire of time, transforming the spiral galaxy barred into a spiral galaxy " régulière". Beyond of a certain size, the Masse accumulated in the bar compromises the stability of the structure of the bar. The spiral galaxies barred with a great quantity of energy accumulated in their center tend to have small and squat bars. As much of spiral galaxies have a structure of bar, that seems a recurring phenomenon in the development of the spiral galaxies.

Bulbs

By studying the core of the Milky Way, the scientists discovered that the bulb of the Milky Way had a form of Cacahuète. That leads to the conclusion that all the barred spiral galaxies have a core of this form.

Examples of barred spiral galaxies

Here a table gathering some barred spiral galaxies

See too

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