Star Quest novels (Ben Bova)

2.

"Humankind headed out to the stars not for conquest, nor exploration, nor even for curiosity. Humans went to the stars in a desperate crusade to save intelligent life wherever they found it. A wave of death is spreading through the Milky Way galaxy, an expanding sphere of lethal gamma radiation that erupted from the galaxy's core twenty-eight thousand years ago and now is approaching Earth's vicinity at the speed of light. Every world it touched was...