Messier 67 (also known as M 67 or NGC 2682) is an open cluster, or galactic cluster, in the constellation Cancer. M67's Trumpler class is variously given as II 2 r, II 2 m, or II 3 r. It was discovered by Johann Gottfried Koehler in 1779. Its age is variously estimated at between 3.2 and 5 billion years. The most recently estimated age of four billion years appears to be the most reliable; thus the stars of M67 are most likely slightly younger than the Sun.
M67 is not the oldest known open cluster, but there are very few older ones in the galaxy. Most open clusters have ages less than one billion years, since open clusters are typically distrupted by loss of mass in their youth when hot young supergiants heat up gas which then escapes, by tidal forces, by field stars passing through the cluster, and by escape of stars whose orbits are changed by encounters by other cluster members. M67 is an important laboratory for studying stellar evolution, since all its stars are at the same distance, and also of the same age, except for approximately 30 anomalous blue stragglers, whose origin is not fully understood. |
