Searching for hidden black holes in the hearts of densely-packed globular clusters

Globular clusters serve as natural laboratories for studies of star formation and evolution because they tend to form at the same time from similar initial materials. But NGC 6325, some 26,000 light years from Earth in the constellation Ophiuchus, is of interest for a different reason. Studies have suggested some tightly packed globular clusters may harbour intermediate-mass black holes that subtly affect the motions of surrounding stars. Astronomers are using the Hubble Space Telescope’s Wide Field Camera 3 to study a larger sample of these dense clusters, including NGC 6325, to look for more evidence of the unseen black holes that may be lurking at their cores.

Globular cluster NGC 6325. Click to zoom in. Image: ESA/Hubble & NASA, E. Noyola, R. Cohen