If it were immobile, you'd expect to find old examples spread throughout the galaxy, remnants of older spacefaring civs, on both planets and asteroids. Asteroidal examples would likely be associated with TN mineral deposits, although likely only small and/or low acc deposits, the last uneconomic remnants of a once better deposit, and on planets mostly associated with ruins, although you might also find mysterious UI sites with no apparent abovegound component too... The traces of a city so ancient that nothing remains, or evidence of a Great Scouring, with all visible signs of civilisation having been destroyed by spoilers? Woooooo, spoooooooooooooky, WOOOOOOOOOooooooooooOOOOOOO