Starborne — Robert Silverberg

Fifty men and women are chosen as the crew of the Wotan, in what is certain to be the greatest voyage of exploration in human history. Their mission is to travel to the  furthest reaches of the galaxy in search of inhabitable worlds. The crew is shut off from Earth except for a telepathic link between a crew member and his sister back home. But when that connection is broken, the Wotan is lost in space until it encounters a vast alien presence that forces the crew to question everything they know about life and death.