Barred spiral galaxy
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 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.
- How are bar galaxies formed? from the alpha-Centauri television series (approx. 14 minutes). First broadcast on Dec 7, 2005.