The following outline is provided as an overview of and topical guide to galaxies:

Galaxies – gravitationally bound systems of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few billion (109) stars to giants with one hundred trillion (1014) stars, each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology as elliptical, spiral and irregular. Many galaxies are thought to have black holes at their active centers.

The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang. Previously, as of July 2015, EGSY8p7 was the most distant known galaxy, estimated to have a light travel distance of 13.2 billion light-years away.

Types of galaxies

By morphological classification

Galaxy morphological classification

By nucleus

Active galactic nucleus

By emissions

By interaction

By other aspect

Nature of galaxies

Galactic phenomena

Galaxy components

Galactic cartography

Larger constructs composed of galaxies

Intergalactic phenomena

Fields that study galaxies


Galaxy catalogs

Persons influential in the study of galaxies

See also

References

  1. ↑ Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa
  2. ↑ Galileo Galilei, Sidereus Nuncius (Venice, (Italy): Thomas Baglioni, 1610), pages 15 and 16. English translation: Galileo Galilei with Edward Stafford Carlos, trans., The Sidereal Messenger (London, England: Rivingtons, 1880), pages 42 and 43.
  3. ↑ O'Connor, J. J.; Robertson, E. F. (November 2002). "Galileo Galilei". University of St. Andrews. Retrieved January 8, 2007.
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