Astronomical and Imaging Data

Useful Informations

NGC 6681, also known as Messier 70 (M70), is a compact globular cluster located in the constellation Sagittarius. It’s a scientifically significant object due to its high density and its position in the Milky Way’s galactic halo.

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Key Physical Properties

M70 is approximately 29,300 light-years from Earth and is situated in the inner region of the Milky Way’s halo, making it subject to strong gravitational forces from the galactic center.

• Structure: The cluster is highly concentrated toward its core, classified as a Shapley-Sawyer Concentration Class II. This indicates that the stars are extremely tightly packed in its central region, which has undergone gravitational collapse. This high density is a result of its long-term dynamical evolution.
• Age and Metallicity: The cluster is an ancient stellar system, with an estimated age of over 13 billion years. Its stars are moderately metal-poor ([Fe/H]≈−1.5 dex), consistent with their formation in the early, metal-deficient universe.
• Mass: M70 has a total mass of about 200,000 times that of the Sun.

Scientific Significance

M70’s properties make it a valuable target for research on stellar interactions and the dynamics of dense stellar systems.

• Tidal Stream: Recent observations have shown that M70 is part of the Sagittarius Stellar Stream, a long stream of stars that were tidally stripped from the Sagittarius Dwarf Spheroidal Galaxy as it was being accreted by the Milky Way. This connection suggests that M70, like Messier 54, may be an immigrant cluster rather than a native one.
• Stellar Populations: There are two distinct stellar populations in the cluster, with each displaying unique abundances. These likely represent different generations of stars.
• Variable Stars: Five known variable stars lie within M70 broadest radius, the tidal radius, all of which are RR Lyrae variables. The cluster may have two blue stragglers near the core.

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