Gamma Hydrae is a Class G8 third-magnitude star in the constellation Hydra. It is sometimes called Cauda Hydrae or Dhanab al Shuja, meaning "Hydra's Tail" or "the Snake's Tail". Gamma Hydrae is a yellow gas giant, located about 130 light-years from Earth.
In the episode "The Deadly Years" of the original series of Star Trek, crewmembers of the USS Enterprise, including Captain Kirk were afflicted by radiation on Gamma Hydra IV, causing them to age rapidly. Gamma Hydra IV was irradiated by a rogue comet, killing all six colonists there by an unknown radiation type which accelerated the aging of anyone on the surface. In the famous Kobayashi Maru test scenario at Starfleet Academy from Star Trek II: The Wrath of Khan, the Starship Enterprise is diverted away from a training mission to Gamma Hydrae.
Rather than being a classic helium fusing giant of the kind that fills the sky, Gamma only recently shut down its hydrogen fusion. Currently with a dead helium core, the star is in a state of transition in which it is about to make its run to growing to much larger proportions and greater luminosity as the helium core shrinks. By the time the helium core, mashed to vastly higher temperature (100 million Kelvin) and density, fires up to fuse to carbon and oxygen, Gamma will be six times brighter (mostly in the infrared part of the spectrum) and will be nearly five times bigger. It will thereafter shrink to more normal giant proportions rather like Pollux and Aldebaran.
Gamma Hydra IV, as depicted in Star Trek