Outline of galaxies

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.

What type of thing are galaxies?

Galaxies can be described as all of the following:

Astronomical object

Types of galaxies

By interaction

By other aspect

Nature of galaxies

Galactic phenomena

Galactic year – duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy.^[1]
Galaxy formation and evolution
Galaxy merger
Hubble's Law

Galaxy components

Components of galaxies in general
Structure of specific galaxies
- Milky Way components
  - Galactic Center
  - Galactic quadrant
  - Spiral arms of the Milky Way
  - Galactic ridge

Galactic cartography

Larger constructs composed of galaxies

Galaxy groups and clusters (list)
- Local Group – galaxy group that includes the Milky Way
- Galaxy group
- Galaxy cluster
  - Supercluster (list)
- Brightest cluster galaxy
- Fossil galaxy group
Galaxy filament

Intergalactic phenomena

Galactic orientation
Galaxy merger
- Andromeda–Milky Way collision
Hypothetical intergalactic phenomena
- Intergalactic travel
Intergalactic dust
Intergalactic stars
Void (list)

Fields that study galaxies

Astronomy
- Galactic astronomy – studies the Milky Way galaxy.
- Extragalactic astronomy – studies everything outside the Milky Way galaxy, including other galaxies.
Astrophysics
Cosmology
- Physical cosmology

Galaxy-related publications

Galaxy catalogs

Persons influential in the study of galaxies

Galileo Galilei – discovered that the Milky Way is composed of a huge number of faint stars.^[2]^[3]
Edwin Hubble

References

^ Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa
^ 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.
^ O'Connor, J. J.; Robertson, E. F. (November 2002). "Galileo Galilei". University of St. Andrews. Retrieved January 8, 2007.

External links

[akb-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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