Pleiades (star cluster)

The Pleiades (also known as M45 or the Seven Sisters) is an open cluster in the constellation of Taurus. It is among the nearest to earth of all open clusters, probably the best known and certainly the most striking to the naked eye.

Composition

The cluster is about 12 light years in diameter and contains approximately 500 stars in total. It is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions. The arrangement of the brightest stars is somewhat similar to Ursa Major and Ursa Minor (the Little Dipper). The total mass contained in the cluster is estimated to be about 800 solar masses {{ref|Adams}}.

Related Topics:
Light year - Star - Naked eye - Ursa Major - Ursa Minor - Solar mass

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The cluster contains many brown dwarfs - objects with less than about 8% of the Sun's mass which are not heavy enough to become proper stars. They may constitute up to 25% of the total population of the cluster, although they contribute less than 2% of the total mass {{ref|Moraux}}. Astronomers have made great efforts to find and analyse brown dwarfs in the Pleiades and other young clusters, because they remain relatively bright and observable, while brown dwarfs in older clusters have faded and are much more difficult to study.

Related Topics:
Brown dwarf - Sun

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Also present in the cluster are several white dwarfs. At the young age of the cluster, normal stars would not be expected to have had time to evolve into white dwarfs, a process which normally takes several billion years. It is believed that rather than being individual low- to intermediate-mass stars, the progenitors of the white dwarfs must have been high-mass stars in binary systems. Mass transfer from the high-mass star to its companion during its rapid evolution would result in a much quicker route to the formation of a white dwarf.

Related Topics:
White dwarf - Binary system

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