Convergence — Charles Sheffield

In the beginning, humans traveled to the stars at a slow sublight crawl. Then they found the Bose Network, which allowed ships to jump instantaneously from one node in the galactic arm to another. Once in the network, they found the Artifacts, enigmatic structures millions of years old left by a vanished race. Incomprehensible to both human and nonhuman minds, the Artifacts seemingly defy natural law. Now, after millions of years, a new Artifact has appeared--and the other Artifacts are showing strange behavioral changes. A motley crew of human and alien scientists and adventurers sets out to inspect. But they should have considered the fact that some changes are more dangerous than others.