This article might have further canon details available on PathfinderWiki.
The Starstone is a magical artifact dating back before the Gap that is now housed on Absalom Station. It acts as an incredibly powerful Drift beacon, attracting Drift engine-powered ships from across the galaxy. The Starstone was once located on Golarion, where it allowed mortals to ascend to godhood.
Besides acting as a powerful Drift beacon, the Starstone also powers Absalom Station, a phenomenon that even the priests of Triune can't explain.
The Strong Absalom movement believes that the Starstone is the sole property of Golarion's refugee races (humans, dwarves, etc.), and that all others should either be heavily taxed for using it as a Drift beacon, or else be completely forbidden from using it.