They used the UV-Visual Echelle Spectrograph of the Very Large Telescope at Cerro Paranal to measure the beryllium content of two stars in the cluster.

In 2006, a study of NGC 6397 using the Hubble Space Telescope was published that showed a clear lower limit in the brightness of the cluster's population of faint stars.

[11] In February 2021, the core of NGC 6397 was reported to contain a relatively dense concentration of compact objects (white dwarfs, neutron stars and black holes), based on the movement of stars near the core derived from data gathered by the Hubble Space Telescope and the European Space Agency's Gaia spacecraft.

Indeed, another group of scientists shortly responded, claiming that because NGC 6397 has undergone core collapse, it should have started dense enough to speed its rates of dynamical interactions, and its original black hole population should be almost entirely gone.

[5] This new work showed that the fits of the central mass excess in NGC 6397 from observed data agreed remarkably well with numerical simulations accounting for a population of hundreds of massive white dwarfs, and essentially no black holes.