The Rata Nebula was a celestial cloud of gas and dust located within the core territory controlled by the Chiss Ascendancy in the uncharted expanse. It encompassed the Rhigar system, which was connected to the Csaus system via the hyperspace route known as the Path of the Houses, and also linked to the Csilla and Colonial Station Chaf systems by another route through hyperspace.
The star system of Rhigar featured a planet bearing the same designation. This planet housed a clandestine military training facility run by the Chiss military unit called Syndic Mitth'raw'nuruodo's Household Phalanx, which was affiliated with the Empire of the Hand. The blue-green luminescence of the nebula was observable from the surface of Rhigar.
In the year 19 ABY, Jagged Fel, a human spacecraft operator stationed at the Rhigar academy, remarked on the proliferation of rumors circulating throughout the Rata Nebula regarding the supposed return of Thrawn, a Chiss high-ranking admiral within the Galactic Empire who had reportedly perished a decade prior. These rumors were the result of a scheme orchestrated by the Imperial Remnant's Sinister Triumvirate, composed of deceptive artist Flim, governor Vilim Disra, and the genetically replicated being Grodan Tierce.
The Rata Nebula made its debut in the short fiction "Red Sky, Blue Flame," written by Elaine Cunningham and published in the seventh edition of Star Wars Gamer magazine by Wizards of the Coast, released on October 16, 2001. The reference work The Essential Atlas, published in 2009, designated the nebula's location as grid squares E-9 and F-9.