Галактикадағы NGC 6397 шарлы жұлдыздар шоғыры

Globular cluster of stars in the Milky Way
NGC 6397 is one of at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse,

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. The respective study argued that black holes could dominate the mass budget of this concentration, if the black holes were not ejected by means of dynamical interactions. 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. This group provided dynamical simulations that showed that a concentration of white dwarfs could explain the first measurement. Finally, in 2022, a work was published by the former scientists, along with one of the leaders of the latter group, and other experts of Hubble and Gaia data. 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.

Hubble pictures revealed many distant globular clusters in galaxies far behind NGC 6397.