M54

Messier 54, abbreviated M54, is a globular cluster in the southern sky within the constellation Sagittarius. It is also known as NGC 6715. Discovered by Charles Messier in 1778, M54 is notable for its association with the Sagittarius Dwarf Spheroidal Galaxy, a satellite of the Milky Way currently undergoing tidal disruption.

Astrophysical estimates place M54 at about 87,000 light-years from the Sun, near the center of the Sagittarius Dwarf. This positions the cluster in the outer Galactic halo region and physically within an accreted system rather than in the main Milky Way disk.

M54 is ancient, with an age comparable to other globular clusters, around 12 to 13 billion years. It has low metallicity, typical of primordial stellar populations, with [Fe/H] values around −1.5. The cluster is relatively massive for a globular, containing hundreds of thousands of solar masses, and it is densely packed toward its core.

Because M54 lies in the core of the Sagittarius Dwarf, its study informs understanding of the Milky Way's assembly history and the processes by which dwarf galaxies contribute globular clusters to larger galaxies during mergers and accretion events.