In Star Trek, a black cluster is a type of cluster that is created when numerous protostars collapsed in close proximity to one another. The result of this collective collapse was an area of space that absorbs energy and dangerously affects spacecraft systems. In 2368, the SS Vico was assigned to explore a black cluster, located in Sector 97. This particular cluster that was formed about 9 billion years ago, from hundreds of collapsed protostars, and was seven times more massive than any black cluster that had been previously sighted. After Starbase 514 lost contact with the Vico the USS Enterprise-D was sent to investigate. Upon its' arrival on the edge of this black cluster, the destroyed hulk of the Vico was immediately found. The Enterprise itself was almost destroyed while further investigating the Vico's disappearance. (TNG: "Hero Worship").

The Federation space station Deep Space 3 is located near a black cluster. (TNG: "Interface")

There are no 'black clusters' in real astronomy. When proto-stars collapse, they get hotter and may be formed into true stars. A proto-star is a star that has not yet initiated fusion. Stars begin their life as a cool cloud of gas. Under its own gravity, the cloud begins to collapse. As it collapses, it releases its gravitational energy as radiation. So a young star is cool but bright. We usually don't see these proto-stars, however, because they are generally shrouded in dust and only give off light in the far infrared part of the spectrum. The proto-star continues to collapse, and as it does, it gets hotter and hotter. "Stars" less than a percent of the Sun's mass eventually halt their collapse due to gas pressure. These stars are "brown dwarfs" or "giant planets," like Jupiter. They never ignite their hydrogen, and gradually dim away.

Stars larger than about 0.05 to 0.07 solar masses contract, getting hotter and hotter, until their cores are hot enough to begin burning hydrogen. When a star "turns on" its hydrogen-burning phase, we say that it has reached the main sequence, and is a true star, not a protostar, brown dwarf, or planet.

While there are no 'dark clusters', there are dark nebulae - 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.