A black cluster is a type of cluster that is created when numerous protostars collapsed in close proximity to one another. The result of this collective collapse is an area of space that absorbs energy and dangerously affects spacecraft systems. Prior to 2368, the Federation maintained reports from ships traveling through black clusters indicating sensor difficulties.
In 2368, the SS Vico was assigned to explore a black cluster, located in Sector 97. This particular cluster was formed about 9 billion years ago, from hundreds of collapsed protostars, and was seven times more massive than any black cluster that had been previously sighted. After Starbase 514 lost contact with the Vico the USS Enterprise-D was sent to investigate. Upon its arrival on the edge of this black cluster, the destroyed hulk of the Vico was immediately found. The Enterprise itself was almost destroyed while further investigating the Vico's disappearance. (TNG: "Hero Worship")