Hearthspace — Stephen Baxter

A thousand years has passed since a human expedition was launched to the system of the 'Hearth', a dark matter star. Humanity - its origins forgotten - has peacefully colonised many planets. But now an expansive slaving culture begins to cross Hearthspace . . .

Ulla Breen, young space-navy officer, must lead the fight against the slavers, and ultimately seek out the origin of humanity in the Hearthspace.