M75 is about 67,500[3]light years away fromEarth and is 14,700[6] light years away from, and on the opposite side of, theGalactic Center.[9] Its apparent size on the sky translates to a true radius of 67 light years.[5] M75 is classified as classI, meaning it is one of the more densely concentrated globular clusters known. It shows a slow rotation around an axis that is inclined along aposition angle of−15°±30°.[3] Theabsolute magnitude of M75 is about −8.5, equating to 180,000 times moreluminous than theSun (L☉).[8]
The cluster has a half-light radius of 9.1 ly (2.80 pc)[6] with a core radius of about 1.6 ly (0.5 pc) and appears not to have undergonecore collapse yet. The mass density at the core is7.9×104M☉·pc−3.[b][2] There are 38RR Lyrae variable stars and the cluster appears to beOosterhoff-intermediate in terms ofmetallicity.[9] 62 candidateblue stragglers have been identified in the cluster field, with 60% being in the core region.[2]
Messier 75 is part of theGaia Sausage, the hypothesized remains of adwarf galaxy that merged with theMilky Way.[10] It is a halo object with anorbital period of 0.4 billion years to travel around the galaxy on a very pronounced ellipse, specificallyeccentricity of 0.87. The apocenter (maximal distance from Earth) is about 57,000 ly (17,500 pc).[3]
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters",Harvard College Observatory Bulletin,849 (849):11–14,Bibcode:1927BHarO.849...11S.
^abFrommert, Hartmut; Kronberg, Christine (2 September 2007),"Messier 75",SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved5 December 2018.
^In a mildly south part of this zone of the sky, +90 declination would give a zenith above the north pole, whereas minus 22 degrees (rounded) precludes it from rising therefore (being above the horizon) at the68th parallel north and hampers visibility at lower latitudes nearby
