Polar-ring galaxy

NGC 4650A, an example of a polar-ring galaxy.

A polar-ring galaxy is a type of galaxy in which an outer ring of gas and stars rotates over the poles of the galaxy. These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy. The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar ring structure.

The first four galaxies that were identified as polar-ring galaxies were NGC 2685, While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.

External links

• APOD: May 10, 1999 - Polar Ring Galaxy NGC 4650A
• Internet Voters Get Two Galaxies in One from Hubble
• X marks the spot in dark matter web - Polar ring galaxies offer first-hand evidence of the existence of the cosmic web, New Scientist, 29 February 2008