Messier 10

M10, otherwise also known as GCI-49, is a rich, bright globular cluster located in the constellation Ophiuchus. The cluster lies at a distance of 14,300 light-years from Earth, at right ascension 16h 57m 8.92s, declination 04°05’58.07” and has an apparent magnitude of 6.4. Its designation in the New General Catalogue is NGC 6254. Messier 10 lies about 16,000 light-years, or 5,000 parsecs, from the galactic centre. It takes roughly 140 million years to complete an orbit around the Milky Way Galaxy. It crosses the plane of the Milky Way’s disk every 53 million years. M10 is moving away from the solar system at a velocity of 69 km/s. The cluster’s estimated mass is 200,000 solar masses.

The cluster was discovered by Charles Messier on May 29, 1764. Messier added it to his catalogue as object number 10, describing it as a “nebula, without stars, in the belt of Ophiuchus; near the 30th star of that constellation, of the sixth magnitude, according to Flamsteed. A decade later, German astronomer, Johann Elert Bode provided a similar description, calling M10 a “nebulous patch without stars; very pale.” It was not until German-born British astronomer William Herschel observed the cluster with a larger telescope that M10 was resolved into individual stars and recognised as a cluster. American astronomer Harlow Shapley was the first to estimate an approximate distance to M10, but his estimation of 33,000 light-years placed the cluster at twice the distance of the modern estimates.

Messier 10 has a spatial diameter of 83 light-years, with its bright central region, which spans roughly 35 light-years. Deep images reveal M10 to span some 20 arc minutes of apparent sky and resolve stars across the entire area of the cluster. The cluster is about two thirds the size of the full Moon, but its outer regions are very dim. In addition, it also appears in close proximity to another object in Ophiuchus, the globular cluster M12. Although they seem to be close together and close in size, the M10/M12 pair are actually separated by some 2,000 light-years. Messier 10 and Messier 12 can be found about half a fist-width west of the bright star Beta Ophiuchi, also known as Cebalrai, with Messier 10 lying a bit lower in the sky, to the south of M12. M10 lies along the line from Cebalrai to Zeta Ophiuchi, the third brightest star in Ophiuchus. It is only a degree away from 30 Ophiuchi, an orange giant star with an apparent magnitude of 4.83. The two clusters lie at an approximate distance of 2,000 light-years from each other and are separated by 3 degrees in the sky. M10 appears brighter because it is about 2,000 light-years closer to us than M12. The best time of year to observe the two clusters is in the months of May, June and July.

Messier 10 contains about 100,000 stars, with the core region consisting of 14 per cent binary stars. Because binary stars are, on average, more massive than normal stars, the binaries tend to migrate toward the centre of the cluster. Although the fraction of binary stars in the core region is about 14%, this proportion decreases with increasing radius to about 1.5% in the outlying regions of the cluster. Four variable stars have been discovered in this cluster. The cluster is classified as moderately metal-poor and there is evidence indicating that it is enriched by elements produced in Type II supernovae and the s-process (slow-neutron-capture process)  in massive stars. The stars in M10 have only 3.5 per cent of the heavy elements found in the Sun, pointing to an age of 11.4 billion years. This makes M10 one of the younger globular clusters known. The central region of M10 contains many blue stragglers, stars formed 2-5 billion years ago that look younger than they are because they are bluer and more luminous than their neighbours. The phenomenon is believed to be a result of interactions between two or more stars in the dense, compact central regions of globular clusters. Four variable stars have been discovered in M10. The cluster’s core will be the last part to survive and will likely be around for another 15 to 20 billion years. It will eventually be torn apart by gravitational forces of the Milky Way as it keeps passing through the galactic disk. Credits: Messier Objects, NASA, Universe Today, Wikipedia.