B-Gamma Maelstrom

The B-Gamma Maelstrom was a known navigational hazard, a spacial whirlpool encountered in the 23rd century.

The maelstrom was known as the “nightmare pool of space.” Its position was within a star system, in visual range of a ringed planet and a few other celestial objects, located between Starbase 6 and the Omega system, which was within the potential political reach of the Klingon Empire. It was also somewhat near Beta II. Its pull was described as almost supernatural. Once a starship was drawn into the hazard, currents jumbled instruments and made navigation nearly impossible. It was a single, continuous spacial phenomena, as opposed to cosmic storms or ion storms which appeared unexpectedly and lasted for short periods.

History
In the year 2266, Hikaru Sulu was ordered to change course and divert the USS Enterprise (NCC-1701) through the maelstrom. He observed that no ship had survived passage through that hazard. The Enterprise diverted briefly into it and was almost ensnared, but was able to thrust forward at warp 8 and escape. 

Later in 2266, while tracking a Klingon battlecruiser, a disturbance appeared and grew rapidly near the Enterprise, erupting into what was called a cosmic storm. Kirk encouraged the crew by saying that nobody before them had survived the B-Gamma Maelstrom, and that they would survive this as well. That storm dragged the ship into a pocket universe. 

Background

 * Given that the phenomena was near Starbase 6 rather than in the Gamma Quadrant, its name suggested that it was a spacial storm that emitted high levels of gamma radiation. Gamma rays were extremely high-energy photons, a form of electromagnetic radiation that ionized atoms and was harmful to life. Cosmic rays colliding with normal matter could generate them, as well as pulsars and quasars.
 * High levels of radiation, also seen in cosmic storms, were known to overwhelm starship shields and expose a crew to various types of radiation.
 * Since gamma-ray generating phenomena were ionizing, the maelstrom might have been considered to be a quasar-like phenomena of the type that the Enterprise was under orders to investigate whenever they were encountered.