Luyten 726-8 is a binary system, home of two stars: BL Ceti and UV Ceti. Both are red dwarves or M-Type Stars. They are among the closest stars to the Solar System and hence they have been closely studied. Among them, UV Ceti is among the most extreme Flare Stars, very eruptive and it has been quoted in many sci-fi novels as home to pirates, outlaws, mafia and terrorist groups.
The two stars have similar masses (10% of Sol), similar radiuses (14% of Sol) and similar luminosities (0.005% of Sol). Their temperatures are also similar, 2600K. Still, BL Ceti is slightly bigger by a few percent.
Both stars orbit around a common barycentre. Their orbits show high eccentricity (0.62), which implies that the distance between them varies between 2 and 9 AU. As so, there are strong tidal forces between them. Stable orbits exist at maximum 0.3 AU around each star. In addition, there is a possibility that planets might orbit further away, at over 30 AU from both stars. A habitable zone must be around 5 million km (0.03 AU) away from any star.
We don't exactly know the age of the system. Because UV Ceti rotates fast, it appears that Luyten 726-8 is younger then the Solar System.
UV Ceti is the archetypal for flare stars. The image on top-right shows UV Ceti through telescope during a flare. The bright dot visible to right is BL Ceti without flares. There have been documented instances when, during a flare, UV Ceti increased its brightness by 100 times within seconds. Each flare is accompanied by massive emissions of UV and X rays, in doses that are lethal for life. Flares would sterilize life on a planet in the habitable zone. BL Ceti has less powerful flares, but still strong enough to endanger life on any habitable planet. In addition, flares would erode any atmospheres over short periods of time.
UV Ceti rotates very fast (around 0.2 days). It is this fast rotation that feeds a powerful magnetic field. As red dwarves have convection currents, which mix matter between the core and the outer layers, bubbles in the magnetic fields often occur, creating shortcuts within the magnetic lines and triggering massive flare events. From Earth, these things cannot be directly observed and flares appear rather randomly and without warnings. However, a civilization living in the system should be able to predict flare events and take cover before they occur.
The rotation period for BL Ceti is not known but is longer. This might explain why BL Ceti is less active.
Both stars create an unusual Stellar Wind. Without flares, both stars have stronger winds then the Sun above their surfaces, but far weaker then the Sun at the same distance. The heliosphere extends up to 10 or 20 AU. However, flares are massive corona ejections, able to push really far into the interstellar environment, up to 100 AU. When the flare of one star spreads towards the other one, a shock zone forms somewhere between the two. Based on all these facts, we know that the heliosphere around Luyten 726-8 has a complex and non-spherical shape, with expanding lobes corresponding to flares and large dips. Any outer planet is periodically exposed both to stellar wind and to interstellar environment.
There have been claims of wobbles in the orbits of both stars, especially BL Ceti, which made astronomers suggest that planets might exist. However, as for today (2022), there is no clear evidence that a planet actually exists in the system. On the other hand, scientists have not ruled out the possibilities of a planet orbiting any of the stars or both at high distance.
How would an Inner Planet look like? A planet orbiting UV Ceti would have no atmosphere, as flares would erode it within millennia. A planet orbiting BL Ceti would be able to hold an atmosphere for longer, but not more then a hundred thousand years. Experiencing strong tidal forces, such a planet will have a powerful volcanism. It would be a hellish landscape, with a barren surface, scourged by flares and dotted with volcanoes and rivers of lava. The red light coming from the two stars will certainly contribute to the hellish landscape. Experiencing high temperature fluctuations, rocks will gradually break apart into fragments and dust. Volcanic ash will add over the surface. As usually volcanic rock and ash is dark in colour, the planet will look dark red.
Experiencing strong tidal stresses, an inner planet might have an internal dynamo and a magnetic field. However, it is basically impossible that a planet could have a magnetic field strong enough to deflect the flares of UV Ceti. There would be spectacular auroras, largely visible from all over the planet.
How would an Outer Planet look line? A planet orbiting both stars at over 30 AU would be able to hold its atmosphere. Such a planet would experience temperatures below -230 C. It will be a place like Sedna close to its aphelion. Both stars would give a combined light comparable with the full Moon. Flares would be the only moments when one would be able to see properly without an additional source of light.
If planets do exist either around UV Ceti or BL Ceti, they cannot be terraformed. Both stars are eruptive and both emit almost all their light in infrared, with little in visible spectra. Given the devastating force of flares, plants need to grow in shelters, away from sunlight. Spaceships need to avoid flares at all costs. During a flare, everyone needs to hide underground.
Colonies on outer planets will be engulfed in darkness. Settlers will have enough light to see without artificial light sources only during flares. They will need to protect themselves from the extreme coldness of space.
Will people come to such an unfriendly world like UV Ceti? We can find an answer in the many books written about it. Two Soviet and two books from the West describe UV Ceti as a place with very unfriendly people.
The system Luyten 726-8 (and especially its star UV Ceti) appears in many sci-fi novels. However, in almost all cases, UV Ceti is depicted as a place for criminals, outlaws, fugitives, mafia quartels and pirates.
According to one Soviet sci-fi novel, Space Horde, UV Ceti was doomed from the beginning. When the Interstellar Space Authority built its Space Stations, it built one in UV Ceti too, but it was destroyed by a flare soon after. The corporation spent a lot of money on attempts to terraform planets around both stars (which actually was a huge money laundry). They knew that terraforming would be impossible. More then this, the corporation, in exchange of huge briberies, allowed criminals and drug lords to escape to UV Ceti. As time passed, strong mafia-style organizations developed in the system. Protected by darkness, by the extremely unfriendly environment surrounding UV Ceti, mafia-style groups colonized the entire Luyten 726-8 system, using former workers as slaves and becoming known as pirates. Their main activities are listed as robberies, assassinations, production and traffic with drugs, weapons and people. Their main source of revenue is slave trade. Slaves are grown in body farms and trained for the purpose they will be sold for. The author then puts an end to this extreme form of human exploitation when slaves rebel against their owners and build on their own a perfect socialist society.
A second Soviet sci-fi novel, Sword Between Fire And Ice, describes UV Ceti as home of a highly depraved society, where the rich enjoy to kill the weak for pleasure and enjoy gladiator fights, while the poor are flogged and tortured all the time.
Another novel, probably influenced by the first one, depicts UV Ceti as a paradise for pirates that earn most of their money producing and selling slaves. The novel describes scenes of extreme cruelty. It focuses on a captured slave, Angela Northern, that kills her owner and takes over his body farm, then starts a war against other pirates. Slowly, she unites all factions inside UV Ceti. After this, she starts a crusade against all other states, federations and empires in the galaxy. She conquers everything in her way, killing without mercy everything she encounters. After conquering the whole galaxy, she commits suicide, so that she will not get old and see her empire falling apart.
A fourth account comes from another novel, where, for the sins of people in UV Ceti, they are punished by their divinity to be eaten by a grey goo, which in the end devours all planets, the two stars and consumes everything until there is nothing left from the whole system but a black hole. Their sins consist of torture, rape (in fact Rape is the name of the king of planet II orbiting UV Ceti) and drug sell and production.
Having four accounts of Luyten 726-8 as a wicked, sullied world, with no account of it as a peaceful and friendly place, there is a significant chance that in the future UV Ceti will be a name associated with evil, terror and many similar negative connotations.