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Elliptical galaxy
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<p>An elliptical galaxy is a type of <a href="/facts/Galaxy/zCyUvEf7">galaxy</a> with an approximately <a href="/facts/Ellipsoid/pe9vm0Sh">ellipsoidal</a> shape and a smooth, nearly featureless image. They are one of the three main <a href="/facts/Galaxy_morphological_classification/AGbMJ9Dp">classes of galaxy</a> described by <a href="/facts/Edwin_Hubble/fpX3JlbJ">Edwin Hubble</a> in his <a href="/facts/Hubble_sequence/LXD95esK">Hubble sequence</a> and 1936 work <i>The Realm of the Nebulae</i>, along with <a href="/facts/Spiral_galaxy/hRT2dtxJ">spiral</a> and <a href="/facts/Lenticular_galaxy/UuG7XJYf">lenticular</a> galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies with their intermediate scale disks, a subset of the "early-type" galaxy population. </p><p>Most elliptical galaxies are composed of older, <a href="/facts/Stellar_evolution/Qa4vAGmn">low-mass stars</a>, with a sparse <a href="/facts/Interstellar_medium/mokU0WEz">interstellar medium</a>, and they tend to be surrounded by large numbers of <a href="/facts/Globular_cluster/FL0EERJU">globular clusters</a>. <a href="/facts/Star_formation/SMyfVDY6">Star formation</a> activity in elliptical galaxies is typically minimal; they may, however, undergo brief periods of star formation when merging with other galaxies. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the <a href="/facts/Virgo_Supercluster/kUNskKbo">Virgo Supercluster</a>, and they are not the dominant type of galaxy in the universe overall. They are preferentially found close to the centers of <a href="/facts/Galaxy_cluster/BhIEgbx8">galaxy clusters</a>. </p><p>Elliptical galaxies range in size from dwarf ellipticals with tens of millions of stars, to <a href="/facts/Type-cD_galaxy/1n0mMurr">supergiants</a> of over one hundred trillion <a href="/facts/Star/PFbd6ICx">stars</a> that dominate their galaxy clusters. Originally, Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false, although the accretion of gas and smaller galaxies may build a disk around a pre-existing ellipsoidal structure. Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies. </p>