From Bravo Fleet Infobase
Grid B1, Delta Quadrant
Diameter: 3 warp-days (10 light-years)
Nebula in the Round Table noted for its extremely high ionic particle concentrations. First charted by the U.S.S. Excelsior in October 2384, it was originally believed to be largely unremarkable aside from its unusual composition. However, after a series of disturbing apparitions aboard the ship, Chief Science Officer Kestra J'naya discovered that the Nebula’s high silicon distribution causes it to function as a single enormous computer, controlled—very erratically—by unconscious thoughts. Effectively, the Excelsior’s entering the nebula turned the entire region into a vast holodeck controlled by the crew's own deepest fears and desires. This was not nearly as fun as it sounds.
The effect is now referred to as the “echo anomaly,” and the nebula was named in honor of the first human explorer to encounter advanced holographic technology. A warning buoy has been deployed at the heart of the nebula, advising passing starships to make a three-to-four day detour around the nebula rather than entering it.
There is no known life or intelligent force living within the bounds of the Nebula. The "echo effect" is purely an accident of chemistry.