Disc galaxy

Disc galaxies are galaxies characterized by a disc, a flattened circular volume of stars. These galaxies may or may not include a central non-disc-like region (a galactic bulge).

Disc galaxy types include:

Galaxies that are not disc type are elliptical galaxies (type dE) and irregular galaxies (type dI).

Disc (galaxy)

A disc is a component of disc galaxies, such as spiral galaxies, or lenticular galaxies.

The galactic disc is the plane in which the spirals, bars and discs of disc galaxies exist. Galactic discs tend to have more gas and dust and younger stars than galactic bulges or galactic haloes.

The galactic disc is mainly composed of gas, dust and stars. The gas and dust component of the galactic disc is called the gaseous disc. The star component of the galactic disc is called the stellar disc.

Inconsistent orbital velocities of stars

It has been noted that the orbital velocity of stars in the disc of most disc galaxies is inconsistent with the amount of luminous matter calculated for the galaxy. A possible explanation for this problem is the non-luminous dark matter.

See also

Further reading