Survival

Ben Bova continues his hard SF Star Quest series which began with Death Wave and Apes and Angels.
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In Surivival, a human team sent to scout a few hundred lightyears in front of the death wave encounters a civilization far in advance of our own, a civilization of machine intelligences.

These sentient, intelligent machines have existed for eons, and have survived earlier "death waves," gamma ray bursts from the core of the galaxy. They are totally self-sufficient, completely certain that the death wave cannot harm them, and utterly uninterested in helping to save other civilizations, organic or machine.

But now that the humans have discovered them, they refuse to allow them to leave their planet, reasoning that other humans will inevitably follow if they learn of their existence.
The Star Quest Trilogy

#1 Death Wave

#2 Apes and Angels

#3 Survival