Class J nebula
A class J nebula or dark nebula was a type of nebula.

The  entered a class-J nebula in 2376 to collect deuterium, where, according to Neelix, it inadvertently picked up an electromagnetic lifeform. It later returned the lifeform to a similar nebula. ()

Class J nebulae containing ionized gas could contain a warp core explosion. The  ejected its sabotaged warp core into such a nebula during the Antarian Trans-stellar Rally in 2377, to protect those attending the race. ()

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Celestial objects