Messier 75 (NGC 6864)

From time to time I obtain data sets from remote observatories, and one of these providers is the Goldfield Astronomical Observatory in Australia, which offers high-quality data from its southern-hemisphere telescopes. Among the datasets I received was a deep image of the globular cluster Messier 75, located in the constellation Sagittarius.

M75 is one of the most compact and densely concentrated globular clusters in the entire Milky Way, classified as concentration class I, the highest on the Shapley–Sawyer scale. This extreme central density gives the cluster a brilliant, almost star-like core when observed at long focal lengths. M75 lies at a distance of roughly 67,000 light-years from Earth and about 14,000 light-years from the Galactic center, placing it far out in the Milky Way’s halo. Its stellar population is predominantly old—on the order of 12–13 billion years—making it an important fossil remnant of the Galaxy’s early formation epoch.

The cluster is also of particular interest because its chemical composition suggests it may have originated in a dwarf galaxy that was later accreted by the Milky Way, a scenario supported by its current orbital characteristics. High-quality remote data, such as this set from Goldfield Observatory, reveal not only the dense stellar core but also numerous faint background galaxies shining through the halo of this ancient cluster.

Data calibration and registration and the final processing was done with PixInsight. The result was as follows: