Graveyard of stars black hole mystery.
At the core of the dense globular star cluster NGC 6397 lies an unexpected stellar graveyard.
Globular clusters are spherical groups of stars tightly bound by gravity.
For years, astronomers have debated whether mid-sized black holes might exist in globular clusters.
These “intermediate-mass” black holes are the long-sought missing link in black hole evolution.
They are smaller than the supermassive black holes that lie at the centers of large galaxies...
...but larger than stellar-mass black holes formed when massive stars collapse.
Scientists hoped to find an intermediate-mass black hole at the heart of this globular cluster...
...but instead, they found stellar-mass black holes lurking there, the remains of collapsed stars.
Astronomers found them using observations from the Hubble Space Telescope…
...combined with data from the Gaia space observatory.
Spanning several years, these observations measured tiny apparent motions of stars in the cluster.
From these motions, this research calculated how mass is distributed throughout the cluster.
The results suggested the stars were orbiting not one intermediate-mass black hole...
...but a tight concentration of stellar remnants with small black holes dominating its mass.
This is the first time a collection of stellar-mass black holes has been found in the core of such a dense globular cluster like NGC 6397.
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