In Star Trek, dark matter nebulae are accumulations of dark matter, that are difficult to detect on sensors unless illuminated by metreon particles. (ENT: "First Flight"). When he was a guest aboard the Vulcan starship Yarahla, Captain Jonathan Archer assisted on their study of a dark matter nebula. (ENT: "Breaking the Ice"). A second dark matter nebula was observed by Captain Archer and Subcommander T'Pol in March of 2153. It was named the Robinson Nebula in honor of the late A.G. Robinson. (ENT: "First Flight")

In 2367, the USS Enterprise-D explored the previously uncharted Mar Oscura Nebula. The nebula was littered with spatial deformations, making travel hazardous. (TNG: "In Theory")

In 2371, the USS Voyager encountered trianic energy beings known as the Komar in a dark matter nebula in the Delta Quadrant. (VOY: "Cathexis"). Neelix said that he once lost a warp nacelle on a ship he was piloting through a dark matter nebula. (VOY: "Threshold")

An uncharted dark matter nebula was located in Cardassian space, near a Dominion ketracel-white storage facility destroyed by Captain Benjamin Sisko and his crew in 2374. Sisko ordered his damaged ship into the nebula to escape several pursuing Jem'Hadar fighters, whereupon they crashed on an uncharted planet. (DS9: "Rocks and Shoals")

In astrophysics, some nebula may indeed contain concentrations of dark matter. The famous "Snake" or "S" dark nebula in Ophiuchus, for example, is a concentration of obscuring dust and dark matter in space that is opaque and doesn't let the stars behind show through it. Dark matter is hypothetical matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxies, dark matter and dark energy account for the vast majority of the mass in the observable universe. The observed phenomena which imply the presence of dark matter include the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter also plays a central role in structure formation and galaxy evolution.

All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation: the remainder is called the "dark matter component." The dark matter component has much more mass than the "visible" component of the universe. Only about 4% of the total energy density in the universe (as inferred from gravitational effects) can be seen directly. About 22% is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space. Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics.

The term 'dark matter nebula', however, should not be confused with the real astronomical term 'dark nebula'. This a type of interstellar cloud that is so dense that it obscures the light from the background emission or reflection nebula (e.g., the Horsehead Nebula) or that it blocks out background stars (e.g., the Coalsack Nebula). The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The largest dark nebulae are visible to the naked eye, appearing as dark patches against the brighter background of the Milky Way. In the inner regions of dark nebulae important events take place, such as the formation of stars and masers.