A disc galaxy (or disk galaxy) is a

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

characterized by a

galactic disc A galactic disc (or galactic disk) is a component of disc galaxies, such as spiral galaxies like the Milky Way and lenticular galaxies. Galactic discs consist of a stellar component (composed of most of the galaxy's stars) and a gaseous compone ...

. This is a flattened circular volume of

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s that are mainly orbiting the galactic core in the same plane. These galaxies may or may not include a central non-disc-like region (a

galactic bulge In astronomy, a galactic bulge (or simply bulge) is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the group of stars found near the center of most spiral galaxies (see ''galactic spheroid'' ...

). They will typically have an orbiting mass of gas and dust in the same plane as the stars. Interactions with other nearby galaxies can perturb and stretch the galactic disk. Disc galaxy types include: *

Spiral galaxies Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

: **

Unbarred spiral galaxies A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

: (types S, SA) **

Barred spiral galaxies A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

: (type SB) **

Intermediate spiral galaxies An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleu ...

: (type SAB) *

Lenticular galaxies A lenticular galaxy (denoted S0) is a Galaxy morphological classification, type of galaxy intermediate between an elliptical galaxy, elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-s ...

: (types E8, S0, SA0, SB0, SAB0) Galaxies that are not disc types include: *

Elliptical galaxies An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Re ...

: (type dE) *

Irregular galaxies An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance ...

: (type dI)

References

{{DEFAULTSORT:Disc Galaxy Galaxy morphological types

See also

References