Galaxy

A galaxy is a gravitationally bound system of stars, interstellar gas, dust, and dark matter. The word is derived from the Greek 'galaxias' (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies range in size from dwarfs with just a few hundred million (108) 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, or irregular. Many are thought to have supermassive black holes at their 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 galaxy observed. It has a comoving distance of 32 billion light-years from Earth, and is seen as it existed just 400 million years after the Big Bang.
== See also ==
* Milky Way Galaxy
* Black hole
Category:Galaxies
Category:Astronomical Objects