USS Voyager approaching an erupting astral eddy
An astral eddy is a subspace disruption anomaly. An erupting eddy is shaped like a ring emanating from a whirlpool center. Within the ring there are massive discharges of plasmatic energy. The center however is totally calm. Matter inside the anomaly is exchanged between space and subspace.
Astral eddies form inside interfold layers, between space and subspace. A sufficiently large eddy periodically erupts into normal space via a subspace rupture. The eddy forms, expands, moves, dissipates and collapses back into the interfold layer. Due to the fact that an eddy is highly charged with plasma, it leaves behind an unusual wake of plasma particles that emanate from subspace. This wake produces dangerous levels of radiation. A Human traveling in the wake on a class 2 shuttle can temporarily be protected from the effects with hyronalin and lectrazine.
Astral eddies disable starship propulsion and navigation. They cause turbulence in the levels that transporters cannot be used to beam anything to or from the anomaly. An erupting eddy also produces graviton waves that impact objects further away. Phasers may be able to disperse an eddy when it erupts into normal space.
The phenomenon was first encountered in 2373. A Vostigye science station, in the Delta Quadrant, was torn apart by an astral eddy with the temperature gradient of nine million kelvins. Eddies collapsing back to the interfold layer also trapped a probe and the shuttlecraft Cochrane, while it was gathering plasma particles with bussard collectors from the wake of an eddy. (VOY: "Real Life")