Credits: Keith Turnecliff, Long Itchington
M12 was discovered by Charles Messier in 1764. The globular cluster is located 23,000 light-years from Earth in the constellation Ophiuchus.
It has an apparent magnitude of 7.7 and can be observed with a pair of binoculars most easily in July.
Because globular clusters like M12 have such high concentrations of stars, they often contain binary star systems — systems of two stars that are locked in orbit around each other. As the stars interact, material from one star can be transferred to its companion, producing X-rays in the process. These X-rays serve as a signature of interacting binary systems and many have been detected in M12. This is unexpected because M12 is a relatively diffuse globular cluster, so stars should be less likely to interact than if they were in clusters with a higher concentration of stars.
M12 also has fewer low-mass stars than expected. Astronomers suspect that gravity has ripped many low-mass stars from M12 as the cluster passed through denser regions of the Milky Way during its orbit around the galaxy’s center. M12 is thought to have lost up to one million stars this way.
Facts about M12 by Keith Turnecliff
Messier 12 or M 12 (also designated NGC 6218) is a globular cluster in the constellation of Ophiuchus. It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a "nebula without stars". In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an aperture of 8 in (20 cm) or greater. In a 10 in (25 cm) scope, the granular core shows a diameter of 3′(arcminutes) surrounded by a 10′ halo of stars.