Warp (galaxy)

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Image of a spiral galaxy in edge position in visible light with an S-shaped bent disk
Infrared image of the spiral galaxy NGC 5907 with warp at the edges

A warp (English for deformation ) is an S-shaped deformation of spiral galaxies perpendicular to the disk plane. In most galaxies, this deformation begins predominantly at the outer edge of the star-rich visible part of the disk plane and extends into the star-poor, invisible outer areas of the disk, which are largely made up of neutral hydrogen . Warps can therefore mainly be observed with the help of radio astronomy in the 21 cm band . In some galaxies such as ESO 510-G13 the curvatures extend into the star-rich inner disk and can be observed with optical telescopes . The disk of the Milky Way system is also bent in its peripheral areas.

Warps were first recognized in 1976 by Renzo Sancisi in the outer areas of galaxies in edge position . However, its exact cause is not yet known. They may have been caused by the tidal action of passing galaxies, but warps can also be observed in isolated galaxies . A favored explanation is halos of dark matter around galaxies in the form of ellipsoids , which are inclined towards the plane of the respective galaxy. This dark matter is also held responsible for the otherwise inexplicably fast rotation of spiral galaxies.

Computer simulations of the evolution of the galaxies suggest that the cause of the different orientation of the galaxy disk and the halo lies in the merging with dwarf galaxies , which slightly tilt the disk of the larger galaxy during the merging via angular momentum transmission. During its rotation, the galaxy “ejaculates” after its halo for a long time until it gradually realigns itself to the halo of dark matter through internal friction in the galaxy's disk.

This model also fits observations that in some galaxies the warp flattens even further outside and merges into a new disk plane inclined towards the inner disk. A warp would thus only be the transition area from an inner disk dominated by the gravitational effects of the visible matter of the galaxy to an outer disk dominated by the halo of dark matter.

literature

  • Ulrich Klein, Gyula Józsa, Franz Kenn, Tom Oosterloo: Galaxies and dark matter: a new perspective . In: Stars and Space . No. 9 , September 2005, p. 28-36 .

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