Lantaru sector

From Memory Alpha, the free Star Trek reference.

An area of Federation space which was the location of a classified research station studying the Omega molecule in the 23rd century. The project was overseen by Dr. Ketteract. After a single molecule was created, it exploded, destroying the station and causing ruptures in subspace extending several light-years, making warp travel impossible in the region first observed by rescue vessels attempting to reach the station. By the 24th century many people believed it was due to a natural phenomenon. (VOY: "The Omega Directive")

The non-canon game Star Trek: Legacy reveals that T'Uerell, having knowledge of this event, captured the research facilities in the Lantaru sector in order to utilize the Omega molecule. She used the molecule to power a Borg Sphere, which after being destroyed by a task force led by the USS Enterprise, caused the Omega explosion. Admiral Kirk recommended the official report be sealed and the Omega Directive be created following the incident.