Nebula

A nebula is an interstellar cloud of gas and dust. Stars and planets typically form from nebulae collapsing into denser forms due to gravity.

Nebulas in Science Fiction

Nebulas are fairly common in science fiction, especially in visual science fiction as a backdrop to the generally bland black of space.

Nebulae in Star Trek

In Star Trek, nebulae often have exotic properties that hinder the performance of starships trying to operate in or near them. Most nebulae interfere with sensor function to some degree, and some have corrosive effects on starship hulls. Others are inhabited by alien life forms. Sometimes they are referred to as spacial anomalies rather then nebulae.