[zopa]

Set it in Universe N+1 of a multiverse and mix in a tiny dusting of metals and such from Universe N.

Or maybe it’s a synthetic population III star, made for unknown purposes by a now-vanished civilization. You’re allowed to make up whatever you need to get the story going.

[xwdv]

Yea, but science fiction seems cooler when a story uses some plausible setting. In any case, another alternative is just to have a large planet with habitable moons in its orbit. Perhaps the planet itself is dead and too hostile for life, and the residents of the moons travel around it to get to civilizations on other moons.

[h2odragon]

interstellar travel is so pasky, irritating and slow. A civilized culture might well cultivate such systems so that they could have a huge number of worlds in easy range of each other.

Allow them those abilities and you might as well be importing already inhabited worlds from wherever you like, which saves time.