Aliens from a different temporal continuum who incubate their young in natural black holes and mistakenly use the artificial singularity powering a Romulan warbird in Timescape.
The quantum singularity lifeforms appear in the Next Generation episode Timescape. They come from a separate time continuum and need the gravity well of a natural quantum singularity to nurture their young.
In 2369 they place their offspring in what they take to be such a singularity. It is in fact the artificial one that drives a Romulan warbird, and the engine fails. The Enterprise answers the distress call, and an attempted power transfer ends with both ships locked in a bubble of almost frozen time, the Enterprise an instant from a warp core breach.
Picard, Troi, Data and La Forge return by runabout and move through the stilled scene. They find two of the aliens disguised as Romulans, one trying to rescue the young and one trying to stop any interference. Data helps reverse events so that the disaster does not happen.