The Beta Niobe Nebula was the nebula created from the supernova of Beta Niobe in 2269. It was located in the Alpha Quadrant.
In 2399, the location of the Beta Niobe Nebula was labeled in a star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. This nebula was located in neutral space. (PIC: "Maps and Legends")
This nebula was only mentioned in writing.