page_title: Galaxy
section_title: Active galaxy
hierarchical_section_title: Galaxy / Other types of galaxies / Active galaxy
caption_attribution_description: English: The jet emerging from the galactic core of M87 (NGC 4486). The jet extends to about 20 arc seconds (absolute length ca. 5 kly). Composite image of Hubble Telescope observations. The galaxy is too distant for the Hubble Telescope to resolve individual stars; the bright dots in the image are star clusters, assumed to contain some hundreds of thousands of stars each. Original caption: "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87" The data used in this image was collected with Hubble's Wide Field Planetary Camera 2 in 1998 by J.A. Biretta, W.B. Sparks, F.D. Macchetto, and E.S. Perlman (STScI). This composite image was compiled by the Hubble Heritage team based on these exposures of ultraviolet, blue, green, and infrared light. Čeština: Výtrysk plazmatu z jádra galaxie M87, který vychází z okolí černé díry
context_page_description: A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias, literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million stars to giants with one hundred trillion stars, each orbiting its galaxy's center of mass.
  Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many galaxies 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 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.
  Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion to a suggested two trillion or more and, overall, as many as an estimated 1×10²⁴ stars.
context_section_description: A portion of the observable galaxies are classified as active galaxies if the galaxy contains an active galactic nucleus (AGN). A significant portion of the total energy output from the galaxy is emitted by the active galactic nucleus, instead of the stars, dust and interstellar medium of the galaxy.
  The standard model for an active galactic nucleus is based upon an accretion disc that forms around a supermassive black hole (SMBH) at the core region of the galaxy. The radiation from an active galactic nucleus results from the gravitational energy of matter as it falls toward the black hole from the disc. In about 10% of these galaxies, a diametrically opposed pair of energetic jets ejects particles from the galaxy core at velocities close to the speed of light. The mechanism for producing these jets is not well understood.
  Seyfert galaxies or quasars, are classified depending on the luminosity, are active galaxies that emit high-energy radiation in the form of x-rays.
caption: A jet of particles is being emitted from the core of the elliptical radio galaxy M87.
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