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Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae [1] and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge.
A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spiral arms due to density wave theory .
Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms. [91] Our own galaxy, the Milky Way, is a large disk-shaped barred-spiral galaxy [92] about 30 kiloparsecs in diameter and a kiloparsec thick.
First spiral galaxy Whirlpool Galaxy: Canes Venatici: 1845 Lord William Parsons, Earl of Rosse discovered the first spiral nebula from observing M51 (recognition of the spiral shape without the recognition of the object as outside the Milky Way). [22] Notion of galaxy: Milky Way & Andromeda Galaxy: Sagittarius (centre) & Andromeda: 1923
In the majority of spiral galaxies, the average pitch angle lies within the range of 5° to 30°. [13] [23] Spiral arms with a small pitch angle are called tightly wound, while those with a larger pitch angle are called open. [24] The shape of spiral arms is often described in a simplified manner as a logarithmic spiral.
List of galaxies with richest globular cluster systems; List of nearest galaxies; List of galaxies named after people; List of spiral galaxies; List of polar-ring galaxies; List of ring galaxies; List of quasars; Satellite galaxies. List of satellite galaxies of the Milky Way; List of Andromeda's satellite galaxies; List of Triangulum's ...
Scientists spotted an oddly shaped visitor in our solar system in 2017. And it was accelerating in an unexplainable way. The icy object, called ‘Oumuamua, which roughly translates to "messenger ...
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.