| 单词 | star cluster |
| 释义 | star cluster A group of stars that are sufficiently close to each other for them to be physically associated. Stars belonging to the cluster are formed together from the same cloud of interstellar gas and have approximately the same age and initial chemical composition. Because of this, and since the stars in a given cluster are at roughly the same distance from earth, observations of star clusters are of great importance in studies of stellar evolution. There are two types of star cluster. Open clusters (or galactic clusters ) are fairly loose systems of between a few hundred and a few thousand members. The stars in open clusters are quite young by astronomical standards (some as young as a few million years) and have relatively high abundances of heavy elements. Globular clusters are approximately spherical collections of between ten thousand and a million stars. These are very old (of order 1010 years) and have low heavy-element abundances |
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