| early-type galaxy |
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Originally (1926), a term used by Edwin Hubble for tightly wound spiral galaxies (types Sa and SBa), which he considered to be the first stage in a progression through "intermediate" (Sb, SBb) to "late" (Sc, SBc). It is now thought very unlikely that spiral galaxies evolve in this manner and, in this sense, the nomenclature has generally fallen into disuse, though it is encountered occasionally. In modern astrophysics the term is increasingly applied indiscriminately to any type of galaxy that is relatively young as judged from its observed properties. Galaxies at very high redshifts, or galaxies containing large amounts of dust and exhibiting rapid star formation may be loosely described by the adjective "early", used essentially as a synonym for "young". See also: Hubble classification. |