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Galaxies are organized into groups and clusters, often within larger superclusters, that are strung along great filaments between nearly empty voids, forming a web that spans the observable universe. [3] Galaxies have a variety of morphologies, with irregular, elliptical and disk-like shapes, depending on their formation and evolutionary ...
Grand design spiral galaxy – Spiral galaxy with prominent and well-defined spiral arms; Intermediate spiral galaxy – Galaxy type intermediate between a spiral galaxy and barred spiral galaxy; Lenticular galaxy – Class of galaxy between an elliptical galaxy and a spiral galaxy; Ring galaxy – Galaxy with an annular appearance
The giant elliptical galaxy ESO 325-4. An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, [1] along with spiral and lenticular galaxies.
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. [84] 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 ...
Lenticular galaxies (designated S0) also consist of a bright central bulge surrounded by an extended, disk-like structure but, unlike spiral galaxies, the disks of lenticular galaxies have no visible spiral structure and are not actively forming stars in any significant quantity. [7] The Hubble sequence throughout the universe's history [8]
Astronomers refer to the distinctive spiral-like bulge of galaxies such as ESO 498-G5 as disc-type bulges, or pseudobulges. Many bulges have properties more similar to those of the central regions of spiral galaxies than elliptical galaxies. [6] [7] [8] They are often referred to as pseudobulges or disky-bulges.
Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large elliptical galaxies and clusters of galaxies. [5] Our own galaxy, the Milky Way, is contained in the Local Group of more than 54 galaxies. [6]
On the right of the Hubble sequence diagram are two parallel branches encompassing the spiral galaxies. A spiral galaxy consists of a flattened disk, with stars forming a (usually two-armed) spiral structure, and a central concentration of stars known as the bulge. Roughly half of all spirals are also observed to have a bar-like structure, with ...