Each system on the map is defined by some sort of large mass. In the case of jump bridges, this is usually a rogue planet, brown dwarf or comet/asteroid field. But most star systems are primarily defined by the types of their actual stars, and by the worlds they contain.
Many stars (perhaps half) are part of systems with multiple stars. Usually there will be one largest star in the system, and smaller stars in orbit around it. Some systems have two stars of comparable mass, making them binaries in the truest sense. Most systems have planets, but in a binary or trinary system, the distance between the component stars can preclude planets. The stars have to be either far enough apart that local planetary orbits aren’t perturbed too much, or close enough that any planets are outside both stars, in circum-binary orbits.
Red dwarfs
The most common type of star is the red dwarf. These are low-mass stars, often very old, fusing hydrogen slower than larger stars. Many red dwarfs are part of binary or trinary systems, where another star is the primary. Red dwarfs, as their name suggests, have lower frequency light, visibly red, so it’s harder to harvest that energy through organic means, as in photosynthesis. Thus, life is often based on a chemical reaction, or on geothermal energy, or electromagnetism. Any photosynthesis is probably done by very dark color plants.
Lone red dwarfs usually have planets. Those in binary systems only have stable orbits for inner planets, as the larger star will perturb orbits farther out, except for circum-binary planets as noted above.
Any planet close enough to the star to have liquid water on the surface is also slowing in its spin due to tidal drag from the star, until it is locked, with the same face always towards the star. This process can be delayed, or even reversed, by a variety of natural and technological means. Many habitable worlds close to a dwarf are actually moons of larger planets orbiting the star. This gives them a day/night cycle from their orbit around the planet, when they would otherwise have been tidally locked to the star.
In lone dwarf systems, those planets that orbit far enough out are free to rotate for billions of years, but are well outside the habitable zone. These are usually either gas giants, frozen worlds, or asteroid belts. Still, moons of gas giants can have liquid water beneath the surface, heated by tidal stretching from the giant.
Suns
A sun in the Array is a medium-size main sequence star, usually yellow. What we would think of as Earth’s Sun is typical of a sun in the Array. A sun usually has a life span of about 10 billion years.
Though fewer in number than dwarfs, suns are the stars most likely to have planets hospitable to Outsider life. The habitable zone is farther from the star, and planets are more free to spin without tidal locking. A planet with a day/night cycle has a much more regulated temperature across the whole surface. Suns may have binary or trinary companions, but these are usually far enough out from the main star so that their gravity does not keep inner planets from having stable orbits.
Thus, most of the optimally habitable planets are to be found around suns. In some sun systems, there can even be more than one habitable world.
Red giants
All stars go through a giant phase late in their lives, where they have used up most of the hydrogen in their cores, and are now fusing helium and later even heavier elements. When this happens, the star begins to grow, becoming less dense and enveloping more of the system.
Yellow suns late in their stellar evolution only get large enough to become red giants towards the end, before finally losing their outer layers into space and then collapsing into white dwarfs. A red giant may have planets in outer orbits, but most of the inner planets are progressively swallowed during the star’s fullest extent.
White dwarfs
These are the embers of stars that have used up all their nuclear fuel, then swelled up to red giants stars, before casting off their outer shells in novae. Whatever is left after a nova (not a supernova) collapses down to a sphere of extremely dense degenerate matter, consisting mostly of carbon and oxygen.
A white dwarf glows brightly for billions of years after the death of the star, because though it no longer creates more heat through fusion, the residual heat of the core of the star continues to radiate.
Some white dwarfs actually have planets, and it’s possible for one to exist in the habitable zone of the dwarf, though it would have to orbit closely, and thus would quickly become tidally locked. Any closer in than the habitable zone and a planet-sized body will be ripped apart by the tidal forces and some of the remnants would likely become an asteroid field.
Blue giants
Much larger stars have more pressure at their cores as they go through their stellar evolution, and are able to fuse even heavier elements. During the late stages of their lives, they can swell to a billion km wide or more. They only burn for a hundred million years or so, and when they do run out of fuel the consequences are spectacularly disastrous.
The fuel being fused in a giant star’s core continues to produce energy, as elements are fused into heavier elements, which are then fused into even heavier elements, until the fusion produces iron, which does not produce net energy when it fuses. The pressure from the fusion is no longer able to sustain the size, and the giant star collapses so mightily that the rebounding shock wave creates one of the most energetic events in the universe: a supernova. Some of the exploding star is fused from the rebounding energy, and even heavier elements are formed. The remnant then collapses even further than a white dwarf.
Neutron stars
Most supernovae will result in a neutron star left behind, an object even more dense than a white dwarf. A neutron stars can have an intense magnetic field, and the gravity is so intense that anything close to the star will be torn apart and added to its mass. Many neutron stars have a magnetic wobble, causing their magnetic field to send out regular pulses, thus leading to the term ‘pulsar’.
A neutron star can have planets, but these will usually be in far orbits, as anything close would have been destroyed in the supernova. Because a neutron star isn’t fusing material, it isn’t producing heat, though like a white dwarf, it will continue to radiate the stored heat from the core for billions of years. Moons around planets in orbit around the star may still have heat from tidal flexing, and subterranean liquid water.
Black holes
Some stars are so massive that when they go supernova, the subsequent collapse compresses the stellar core beyond even the neutron pressure that holds up a neutron star. When that happens, it continues to collapse, until the escape velocity is greater than the speed of light. What happens after that is conjecture, because nothing from inside that distance ever gets back out to report. The current Array assumption is that the singularity is a particle at the center of the black hole that is equal in diameter to the Planck length of 1.616 × 10⁻³⁵ meters. Nothing can get smaller than that and remain in regular space.
Even a black hole can have surviving companion stars, or even planets in far orbits. Anything of even intermediate distance would be ripped apart by the tidal forces. A black hole can also have a companion main sequence star, and may even be feeding on matter from the companion.