The Z'Tarnis Nebula was a Mutara class nebula at the border of the Romulan Star Empire's Neutral Zone with the Federation. It was considered one of the youngest celestial bodies in the Milky Way Galaxy having expanded after the collapse of the Chodak Empire. In the year 2370 the Nebula was the hideout for the Chodak Unity Device, which was sent there through time from the distant past.
A Romulan fleet which entered the nebula in persuit of the device was destroyed. Later the USS Enterprise-D, the Garidian warbird Asiram and a Chodak cruiser also entered the Nebula seeking to find the ancient device. (TNG video game: A Final Unity)