The Killing Star — George Zebrowski

The immeasurable universe has spawned competitive species...and now one has discovered man.

Only one observer saw the Apocalypse approaching -- but by then it was already too late. In a brief, incomprehensible instant, every inhabited planetary surface in the solar system is wiped clean by relativistic bombs launched by an unknown alien race. Life on Earth and elsewhere has ceased to exist.

All that is left of humanity is a handful of survivors hiding between the planets -- a small, terrified remnant of civilization temporarily overlooked by the intruders' doomsday technology. And now they must find some means of escape before they, too, are detected...and destroyed.