Densely clustered globular cluster NGC 6325 shines in this image from the NASA/ESA Hubble Space Telescope. This dense group of stars is located about 26,000 light-years from Earth in the constellation Ophiuchus.

Globular clusters like NGC 6325 are close-knit collections of stars with anywhere from tens of thousands to millions of members. They can be found in all types of galaxies and serve as natural laboratories for astronomers studying star formation. This is because stars forming globular clusters tend to form at roughly the same time and with a similar initial composition;

Astronomers studied this particular cluster not to understand star formation, but to look for a hidden monster. While it may seem peaceful, astronomers suspect that this cluster may contain a medium-mass black hole that subtly influences the motion of surrounding stars. Previous research has found that the distribution of stars in some very dense globular clusters, where stars are relatively tightly packed, is slightly different from what astronomers expected.

This inconsistency suggests that at least some of these densely packed globular clusters—perhaps including NGC 6325—may have a black hole lurking at the center. To further investigate this hypothesis, astronomers turned to Hubble's Wide Field Camera 3 to observe a larger sample of densely populated globular clusters, which includes this star-filled image of NGC 6325. Additional data from Hubble's Advanced Camera for Research is also included in this image.

 

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