>What *would* do it is the relativistic particles that are expelled
>from the collision. These are thought to be the source of the gamma
>burst (by folks building models of bursters at cosmic distances.)
>These particles would carry much more energy than the gammas,
>and would arrive over a period of centuries (since the particles
>would not travel in straight lines, due to interstellar magnetic
>fields.) They would induce radioactivity in the atmosphere and
>produce secondary particles that would reach the ground.
OK, this makes sense.
Is a relatively (pardon the pun) nearby, but beyond the lethal radius (say
2000 light-years) neutron star binary collapse a plausible cause for mass
extinctions?
I would think that if such events are truly as common as this, the prognosis
for long-term space colonization is poor. It would be very hard for a
space-based civilization to sustain hundreds of years of hard radiation at
such intensity that an atmosphere is insufficient shield. Even planetary
based nanotech using civilizations would be very strained by such events.