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Messier 67 in the Constellation Cancer

Description of object:

With an age of about 4 billion years, M 67 is one of the oldest open star cluster in the galaxy. Only a few star clusters are older, e.g. NGC 188. Due to its relatively short distance of only 2700 light years, M 67 is one of the standard objects for the study of stellar evolution and it is one of the most thoroughly studied star clusters in our Milky Way. However, estimates of its physical parameters such as age, mass and number of stars of a certain type vary considerably in many studies. Many scientific studies focus on the evolution of stars, since all members of M 67 were formed almost simultaneously and have an identical distance from the Solar System.

M 67 includes more than 100 sunlike stars, numerous red giants and about 150 white dwarfs. The cluster does not contain any main sequence stars that are bluer than spectral type F - with the exception of about 30 "Blue Stragglers", whose origin is still unknown. Blue Stragglers are stars that are bluer (hotter) and more luminous than stars of the same age. The total mass of the cluster is estimated at 1100 to 1400 solar masses. The initial mass should have been higher by a factor of 10.
A joint study by Barnes et al. from March 2016 examined the rotation periods of 20 Sun-like stars in M 67 on the basis of brightness variations caused by sunspots. The light curves of these 4 billion old stars show rotation periods of nearly 26 days which is very similar to the rotation of our Sun. The measurements were made with the Kepler Space Telescope. Investigations by ESO in Chile, also dating from 2016, unexpectedly led to the discovery of several 'hot Jupiter' type exoplanets of stars in M 67. The ESO press release can be found here.

With an apparent diameter of almost 30 arcminutes, the absolute diameter is 20 light years, over which some 500 stars are distributed. M67 was discovered in 1779 by the German astronomer Johann Gottfried Köhler.

« The annotated image shows the size comparison with the moon.

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