a hypernova, whose gamma rays can destroy most life on a planet at several thousand light-years, is only lethal if one of its beams make a direct hit, like those of a lighthouse.
This unleashing of stellar fury is apparently caused when two massive black holes collide. Each of its destructive beams contains as much energy as the Sun will release in its 10 billion-year lifetime. A planet struck by such a beam would be sterilized.
Happily these explosions — visible through powerful telescopes — took place in the early universe. The galaxy is ours for the taking, depending on the efficiency of future spaceships. A recent scientific paper predicted: “If faster than light travel becomes possible, humanity will explode into the galaxy like a tsunami.” And there are plenty of habitable worlds out there.