One of the standard solutions to the Fermi Paradox is that are we are not overrun by visitors because technological societies are either short-lived or rarely form. The Gamma Ray burster is often proposed, particularly in science fiction, as a plausible transgalactic killer. A burster sterilizes quite a bit of the surrounding galaxy.
Wired News: Gamma-Ray Burst Mystery UnraveledOur galaxy is about 100,000 light years across, so a 3,500 light year kill zone is only a modest portion of the galaxy. Alas, PSR B1534+12 is not alone. As far as we can tell we live in a reasonably quiet galactic neighborhood; if we have a killer nearby they are likely fairly common elsewhere.
By Robert Zimmerman
02:00 AM Oct. 04, 2005 PT
Astronomers have long theorized that merging neutron stars produce massive explosions capable of wiping out nearby solar systems for thousands of light-years around....
Now a flurry of research is coming to a head that offers the first detailed view of the origin of so-called short gamma-ray bursts, revealing a picture that is consistent with the merging neutron star theory. That means the universe could be far more hazardous than previously thought, given the number of known and probable neutron star pairs in relative proximity to Earth.
... As astrophysicist Tsvi Piran stated at a Hubble Space Telescope symposium in 1999, "Every gamma-ray burst apparently signals the birth of a black hole."
Steve Thorsett of Princeton University has calculated the consequences if such a merger were to take place within 3,500 light-years of Earth, with its energy aimed at the solar system. The blast would bathe Earth in the equivalent of 300,000 megatons of TNT, 30 times the world's nuclear weaponry, with the gamma-ray and X-ray radiation stripping Earth of its ozone layer.
Three such binary systems have been discovered, and one, PSR B1534+12, presently sits about 3,500 light-years away and will coalesce in a billion years.
The earth is about 4.5 billion years old. We find evidence of life 3.5 billion years ago. If we have one billion years left to live  then our world of life is a senior citizen. Of course a billion years is a little while. Time enough, assuming no runaway nanotech, for quite a few life forms to develop technological civilizations on earth.
So perhaps there's a silver lining here. Maybe this research suggests that galaxies have a stable middle age of about 4-5 billion years before the gamma bursters go off across the disc, sterilizing the galaxy. In other words, gamma bursters may be concentrated in time, not evenly distributed across the galactic timeline. If my terribly amateur interpretation is not far off, conditions are not so terrible for the development of interstellar civilizations.
On the other hand, if that's true, where are they? Well, there are other explanations for the fermi paradox ...
 We used to have 3-5 billion until the sun fizzled, but that more remote problem is far more manageable than a gamma burst.
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