ESA Hubble Science Release | 2021 Feb 11
Scientists were expecting to find an intermediate-mass black hole at the heart of the globular cluster NGC 6397, but instead they found evidence of a concentration of smaller black holes lurking there. New data from the NASA/ESA Hubble Space Telescope have led to the first measurement of the extent of a collection of black holes in a core-collapsed globular cluster.
Globular clusters are extremely dense stellar systems, in which stars are packed closely together. They are also typically very old — the globular cluster that is the focus of this study, NGC 6397, is almost as old as the Universe itself. It resides 7800 light-years away, making it one of the closest globular clusters to Earth. Because of its very dense nucleus, it is known as a core-collapsed cluster.
When Eduardo Vitral and Gary A. Mamon of the Institut d’Astrophysique de Paris (IAP) set out to study the core of NGC 6397, they expected to find evidence for an “intermediate-mass” black hole (IMBH). These are smaller than the supermassive black holes that lie at the cores of large galaxies, but larger than stellar-mass black holes formed by the collapse of massive stars. IMBH are the long-sought “missing link” in black hole evolution and their mere existence is hotly debated, although a few candidates have been found ...
Hubble Uncovers Concentration of Small Black Holes
NASA | GSFC | STScI | HubbleSite | 2021 Feb 11
Does NGC 6397 Contain an Intermediate-Mass Black Hole
or a More Diffuse Inner Subcluster? ~ Eduardo Vitral, Gary A. Mamon