One of the explanations for the apparent rarity of life in the universe is the frightening gamma ray burst - perhaps life is astonishingly rare, and Earth has just been lucky to be in a narrow slice of space that for the last five billion years. But (almost?) everywhere else the planetary Petri dishes have undergone regular GRB autoclaving, or at least they got autoclaved before complex nervous systems develop. Putting numbers to this based on the observed distribution of GRBs, a recent paper modeled frequency and distribution of GRBs to estimate the chance over time of a GRB happening close enough to Earth to be life-damaging. Among their conclusions:
1) There's a 50% chance that a life-damaging GRB took place in the last 500 million years. Permian-Triassic extinction anyone?
2) The probability of a system being exposed to life-damaging GRBs goes up as you move toward the center of the galaxy. Many of our SETI efforts focused on our own galaxy have focused coreward, on the reasoning that there are more stars in that direction, therefore more chance of finding life. The reflex to this paper's model is to worry that we're looking in the wrong direction - but if you assume galaxy-colonizers, looking coreward may still be the best strategy - the GRB survivors on the galactic rim would be able to colonize inward.
Paper here.
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