An astral eddy is an extremely powerful and potentially destructive phenomenon formed in an interfold layer at the confluence of space and subspace. A series of astral eddies were encountered by the USS Voyager in 2373 in the Delta Quadrant. These eddies exhibited a temperature gradient of nine million kelvin, massive discharges of plasmatic energy, powerful graviton waves, and a calm eye at the center of the phenomenon, wherein matter was exchanged between space and subspace. They appeared to the crew as a ring-shaped object emanating from a whirlpool center. When they grew sufficiently large, the eddies would periodically erupt from subspace into normal space, and then dissipate, after which a wake of plasma particles emanating from subspace was left behind.
The crew of Voyager first encountered this phenomenon while investigating the destruction of a Vostigye space station, which was destroyed by one of the eddies. Tracking the plasma wake, they encountered another one, which caused the ship's helm and navigational control to go offline. Captain Janeway ordered the ship's phasers utilized in an attempt to disperse the eddy, but before they had a chance to fire it collapsed into itself. The crew later encountered another eddy, which threw off powerful graviton waves causing some difficulty in keeping the ship steady. The crew launched a probe into this eddy, which was pulled into the interfold layer when the eddy collapsed. Later, Tom Paris piloted the Class 2 shuttle Cochrane in an attempt to collect the resultant plasma particles with the shuttle's Bussard collectors, although he required doses of hyronalin and lectrazine to protect him from radiation poisoning. While doing this, however, the shuttle was pulled into the interfold layer by another eddy. Paris was later able to escape by piloting the shuttle into an eddy just as it erupted into normal space. (VOY: "Real Life")