page_title: Galaxy
section_title: Spirals
hierarchical_section_title: Galaxy / Types and morphology / Spirals
caption_attribution_description: Česky: NGC 1300, spirální galaxie s příčkou vyfotografována z Hubbleova vesmírného dalekohledu. English: Barred spiral galaxy NGC 1300 photographed by Hubble telescope. In the core of the larger spiral structure of NGC 1300, the nucleus shows its own extraordinary and distinct "grand-design" spiral structure that is about 3,300 light-years (1 kiloparsec) long. Only galaxies with large-scale bars appear to have these grand-design inner disks — a spiral within a spiral. Models suggest that the gas in a bar can be funneled inwards, and then spiral into the center through the grand-design disk, where it can potentially fuel a central black hole. NGC 1300 is not known to have an active nucleus, however, indicating either that there is no black hole, or that it is not accreting matter. The image was constructed from exposures taken in September 2004 by the Advanced Camera for Surveys onboard Hubble in four filters. Starlight and dust are seen in blue, visible, and infrared light. Bright star clusters are highlighted in red by their associated emission from glowing hydrogen gas. Due to the galaxy's large size, two adjacent pointings of the telescope were necessary to cover the extent of the spiral arms. The galaxy lies roughly 69 million light-years away (21 megaparsecs) in the direction of the constellation Eridanus. Español: NGC 1300, una galaxia espiral barrada. Français&#160;: NGC 1300, une galaxie spirale barrée. Photo prise par le télescope spatial Hubble (HST). NGC 1300, située à 69 millions d'années lumière de nous dans la constellation d'Éridan, fait partie de ces galaxies possédans une grande barre centrale. Cette barre contient une spirale de 3 300 années lumières de diamètre. Les gaz de la galaxie sont attirés vers l'intérieur de la barre puis dans la spirale interne de laquelle ils nourissent un trou noir. Cependant, le centre de la galaxie n'est pas actif, ce qui laisse à penser que le trou noir central n'accrète pas de matière actuellement. La lumière des étoiles et de la poussière est visible en bleu. Celle des amas stellaires est soulignée par le rouge de l'hydrogène. Cette image est issue de l'assemblage de deux clichés pris par la caméra ACS. Nederlands: NGC 1300, voorbeeld van een balkspiraal. Português: NGC 1300, uma galáxia espiral barrada. Suomi: Sauvaspiraaligalaksi NGC 1300. ไทย: ดาราจักรรูปก้นหอยแบบมีแกน NGC 1300 Українська: Смугаста спіральна галактика NGC 1300, сфотографована космічним телескопом Хаббл.
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: Spiral galaxies resemble spiraling pinwheels. Though the stars and other visible material contained in such a galaxy lie mostly on a plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of dark matter which extends beyond the visible component, as demonstrated by the universal rotation curve concept.
  Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type S, followed by a letter (a, b, or c) which indicates the degree of tightness of the spiral arms and the size of the central bulge. An Sa galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an Sc galaxy has open, well-defined arms and a small core region. A galaxy with poorly defined arms is sometimes referred to as a flocculent spiral galaxy; in contrast to the grand design spiral galaxy that has prominent and well-defined spiral arms. The speed in which a galaxy rotates is thought to correlate with the flatness of the disc as some spiral galaxies have thick bulges, while others are thin and dense.
  In spiral galaxies, the spiral arms do have the shape of approximate logarithmic spirals, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant angular velocity. The spiral arms are thought to be areas of high-density matter, or "density waves". As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of the higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars.
caption: NGC 1300, an example of a barred spiral galaxy
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