Messier 36

Lore & Background

Messier 36 was discovered by Giovanni Batista Hodierna before 1654, who described it as a nebulous patch. It was independently re-discovered by Guillaume Le Gentil in 1749, and then Charles Messier observed it in 1764 and added it to his catalogue. The cluster is about 1,330 pc (4,340 light years) away from Earth, though a 2020 study of variable stars estimated a new closer distance of 3,800 light years.

The cluster is very similar to the Pleiades cluster (M45), and if as far away it would be of similar apparent magnitude. It has an angular diameter of 10′ and a core radius of 3.2′. Its mass is roughly 746 M☉, and its linear tidal radius is 10.6 ± 1.6 parsecs (34.6 ± 5.2 ly). Based upon photometry, the age of the cluster has been estimated by Wu et al. (2009) as 25.1 Myr and 26.3+3.2−5.2 Myr by Bell et al. (2013). The luminosity of stars that have not yet depleted their lithium implies an age of 22±4 Myr, in good agreement with these older estimates.

M36 includes ten stars with a visual magnitude brighter than 10, and 178 down to magnitude 14. 38 members display an infrared excess, with one being particularly high. There is one candidate B-type variable star, of 9th magnitude. A young stellar object with an outflow, associated with the infrared source IRAS 05327+3404, was discovered in optical observations of M36. The object is nicknamed 'Holoea,' Hawaiian for 'flowing gas.' Despite appearing close to M36, it is probably not a part of M36, but instead may be a member of the more distant S235 region. The young star driving the outflow was classified as transitional between class I and class II and appears to be surrounded by large amounts of circumstellar material.

Reader's Guide

Messier 36's significance lies in its role as a well-studied open cluster that offers insights into stellar evolution and cluster dynamics. Its similarity to the Pleiades (M45) makes it a useful comparative object for understanding how distance affects apparent magnitude. The cluster's age estimates, ranging from about 22 to 26 million years, come from multiple photometric studies and lithium depletion analysis, showing consistency across methods. The presence of 38 members with infrared excess, including one particularly high, indicates ongoing or recent star formation activity. The discovery of the young stellar object 'Holoea' near M36, though likely not a member, highlights the cluster's location in a region of active star formation. The 2020 study suggesting a closer distance of 3,800 light years introduces uncertainty that may refine our understanding of the cluster's physical properties. M36's legacy is as a key object in Messier's catalogue, representing a northern open cluster that continues to yield data on stellar populations and interstellar phenomena.

Did You Know?

• The cluster is very similar to the Pleiades (M45) and would have a similar apparent magnitude if at the same distance.
• A young stellar object nicknamed 'Holoea' (Hawaiian for 'flowing gas') was discovered near M36 but is probably not a member.