Astronomical and Imaging Data

Useful Informations

NGC 6101 is a globular cluster located in the southern constellation Apus. It’s a scientifically interesting object due to its low stellar concentration and its unusual kinematic properties, which suggest a peculiar formation history.

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Physical Characteristics

• Distance: Approximately 47,600 light-years from Earth and 36,500 light-years from the Galactic Center.
• Mass and Age: It has an estimated mass of about 170,000 solar masses and is very old, with an age of around 12.5 billion years.
• Concentration: NGC 6101 is classified as a Shapley-Sawyer Concentration Class X, indicating a very low stellar concentration and a loosely packed core. Individual stars are easily resolved even with small amateur telescopes.

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Unique Properties

• Black Hole Population: Despite its low stellar density, NGC 6101 is thought to contain a significant population of stellar-mass black holes. While these objects are invisible, their gravitational influence explains why the cluster’s core appears “inflated” and less dense than expected for its age. This finding challenges the long-held belief that globular clusters lose all their black holes due to supernova kicks.
• Lack of Mass Segregation: The cluster shows no evidence of mass segregation, a process where heavier stars sink to the center of a cluster over time. This lack of segregation, combined with its high black hole retention, suggests that a population of black holes in the core has dynamically “stirred” the cluster, preventing the heavier normal stars from settling at the center.
• Kinematics: NGC 6101 is one of the few metal-poor globular clusters in the Milky Way with a retrograde orbit (orbiting the galaxy in the opposite direction of most stars). This, along with its age and metallicity, suggests that it was likely not formed in the Milky Way’s halo but was instead captured from a dwarf satellite galaxy, possibly the Canis Major Dwarf Galaxy.

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