Barred spiral galaxy

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NGC 1300 seen almost from above. Image of the Hubble Space Telescope
NGC 253 , a bar-spiral galaxy with particularly active areas of star formation.

A bar spiral galaxy , or bar galaxy for short , is a spiral galaxy with a more or less straight band of bright stars . This “bar” extends from the center of the galaxy to various distances, in some cases almost to the edge. The spiral arms extend from the ends of the beam.

Edwin Hubble classified these types of spiral galaxies as "SB" (English "Spiral Barred") and divided them into three subcategories according to the shape of the bar and the spiral arms:

  • SBa galaxies have a large, bar-shaped core, the spiral arms are almost closed in a ring.
  • SBb galaxies have more pronounced arms and a weaker core.
  • SBc galaxies have S-shaped arms that are only slightly curved. Instead of a core, they only have a central thickening.

A fourth category was added later:

  • SBm galaxies are dwarf bar-spiral galaxies. According to recent findings, the Large Magellanic Cloud probably also belongs to this group.

Bar spiral galaxies are relatively common. Studies show that up to two-thirds of all spiral galaxies have a bar structure. The Milky Way is also a bar-spiral galaxy.

The area of ​​the bar represents an active star formation area . Gas , from which the stars form, flows from the spiral arms towards the center of the galaxy.

The bar structure is the result of a density wave that spreads radially from the center of the galaxy and affects the orbits of the inner stars.
The structure may also develop as a result of mutual gravitational perturbations of galaxies.

It is believed that bar spirals are only a temporary stage in the evolution of galaxies. The bar spirals develop into "regular" spiral galaxies over time.


Web links

Commons : Barred Spiral Galaxy  - Collection of images, videos and audio files
Wiktionary: bar spiral galaxy  - explanations of meanings, word origins, synonyms, translations