Mirkheim — Poul Anderson

A star explodes. And a billion years later, a galaxy explodes in war. When the heavy metal ruin of Mirkheim is discovered at the edge of Known Space, the gigantic planet becomes the center of a war that is fought in all the far reaches of Earth's dazzling and corrupt empire. This epic adventure of the end of a thousand-year civilization sweeps from hyperspace skirmishes in the radio glare of dark suns, to the bloody deals in the corridors of Earth itself, where the stars are traded like coins.