The Hanoli rift was a subspace rupture that destroyed the Hanoli system in the mid-23rd century. The initial cause of the rift was never determined, with dozens of theories – none of which were confirmed – proposed. What was known was that in the area of the rift there was no wormholes and minimal starship activity.
After spending twelve hours within range of the anomaly, a Vulcan science mission to the rift detonated a pulse wave torpedo at the coordinates of the tear. Five minutes later, the detonation had radically expanded the rift. Subsequently, the expansion destroyed the Vulcans and the star system. The rift imploded when the expansion reached a critical mass point and, soon afterwards, the rift disappeared from normal space. (DS9: "If Wishes Were Horses")