The Galactic Barrier is an energy field of unknown composition and power that surrounds the entire Milky Way galaxy. Only visible to the naked eye and the visual recording equipment at short range, it shines with pink and purple glow, although the crew of the late 21st century explorer vessel S.S. Valiant referred to the phenomenon as ‘The Big Red’ which indicates that the barrier is capable of registering as different colours on the spectrum, although the method for this- like much of the barrier’s workings- are unknown to Federation science. There are also reports that space-time continuum ‘voids’ are present within the barrier, although the manner in which one accesses them is hereto unknown.
Stellar cartography scans carried out by interstellar deep space probes launched in the late 23rd and early 24th centuries show the barrier is not the same consistent size and thickness and may encompass the entire galactic plane- in essence, providing a protective ‘shell’ around the Milky Way. One of the barrier’s thinnest points is near Delta Vega I, in the region now known as the Sagittarius Reach. There is also strong evidence that points to some of the galaxy’s outermost stars being situated within this strange phenomenon.
First encountered by the crew of the Valiant after being swept out of the galaxy by a ‘magnetic space storm’ in 2065;then again by the USS Enterprise two centuries later, the barrier displays an unnerving ability to uplift certain groups of individuals that are ESP-sensitive into omnipotence. This effect seems to also instill those uplifted with megalomania. Extraordinary measures must be taken to stop them (Captain Carlos Tarasco of the Valiant was forced to destroy his own ship when the engineer’s mate threatened to enslave the entire human race and Captain Kirk was forced to bury Gary Mitchell alive under a rockfall when he threatened to do the same). Other individuals report extreme sensory distortions while travelling within the barrier and during the Enterprise’s first trip through nine crew members died of unclassifiable ‘brain damage’.
The effects of the barrier are not just limited to physiological damage. 23rd century shield technology was not able to block out all energy from the barrier and starship hulls could quickly heat up to 2000 degrees centigrade. Ship’s systems are widely affected by travel through it, especially warp drive and main power grids, often leaving vessels stranded for several days until repairs can be completed. Even the significantly more advanced Kelvan vessels of the era were severely damaged by transiting the barrier, although there were no reports of that species being elevated to omnipotence.
As a result of these effects- Starfleet Command took the unusual decision in 2269 to outlaw travel to and transit of the distant barrier. This was the second time that Command prohibited crews from visiting certain places (the first being Talos IV), underscoring the deadly nature of the barrier. In the late 24th century the Quadros XII probe detected decreased mass and energy readings from the barrier and analysts on the Federation Science Council now believe that it is safe to conduct studies on the barrier, albeit with caveats. All manned scans of the barrier must be conducted from 2 million kilometers (the furthest distance that the barrier appears on scanners) and any closer scans must be conducted by unmanned probes. Furthermore, travel into the barrier is strictly prohibited. Additionally, 24th century shielding is now believed to be able to withstand the dangerous effects of the barrier, although this hypothesis remains untested for fear of it being wrong.
As a result, the Federation Science Council in conjunction with Starfleet Command assigned the USS Columbia to the region now known as the Sagittarius Reach (which spans 1000 light years) on a long term exploratory voyage. Additionally, construction of a scientific institute on the planet Delta Vega I (the closest known planet to the barrier) began in January 2395 to compliment the Columbia’s efforts. This is known as Dehner Base (and named for one of the casualties of the Enterprise's first encounter with the barrier). While the Columbia is task with general exploratory duties, Dehner Base’s primary mission is to examine the effect of the barrier of the region’s native species.
The denizens of the Imperial Losarian Commonwealth are aware of the Barrier, referring to it as 'The Great Boundary'.