A black cluster was a type of cluster that was created when numerous protostars collapsed in close proximity to one another. The result of this collective collapse was an area of space that absorbed energy and dangerously affected spacecraft systems. Prior to 2368, the Federation maintained reports from starships 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 nine 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")