Also, a quick note. Cell Bio Guy provided the estimate that supernovas are not a substantial part of the Filter, by noting that the the volume of the galactic disc (~2.6*10^13 cubic light years), a sterilization radius or around 10 light years (3 parsecs about) , and one every 50 years. This gives a sterilization of around 100 cubic light years per year and an odds of sterilization of a star system per year of one in three or four trillion.
To expand on their reasoning: One can argue that the supernova sterilization distance is too small, and if one increases that by a factor of 5 as an upper bound, that increases the amount of sterilized volume by a factor of about 1000, giving a sterilization event per a star system of about one in ten billion which is still very rare. One can also argue that it may be that much of the galactic center is too violent to have habitable life, which might cut down the total volume available by about 20%, and if one assumes (contrary to fact) that none of the supernovas are in that region, this still gives about one event every 6 billion years, so this seems to be strongly not the Filter.
There’s some reason to think that the core is unsuitable for other reasons. There are a few lines of evidence (see link below for one I could find fast) that the core of our galaxy undergoes periodic starbursts every few hundred megayears in which it has a brief episode of very concentrated rapid star formation, followed by a period of a few tens of megayears in which the supernova rate in the core temporarily exceeds the steady state galactic supernova rate by a factor of 50+. The high rate and small volume (less than 1⁄500 the galactic volume) would lead to quite the occasional local sterilization event if this does indeed happen on a regular basis.
Also, a quick note. Cell Bio Guy provided the estimate that supernovas are not a substantial part of the Filter, by noting that the the volume of the galactic disc (~2.6*10^13 cubic light years), a sterilization radius or around 10 light years (3 parsecs about) , and one every 50 years. This gives a sterilization of around 100 cubic light years per year and an odds of sterilization of a star system per year of one in three or four trillion.
To expand on their reasoning: One can argue that the supernova sterilization distance is too small, and if one increases that by a factor of 5 as an upper bound, that increases the amount of sterilized volume by a factor of about 1000, giving a sterilization event per a star system of about one in ten billion which is still very rare. One can also argue that it may be that much of the galactic center is too violent to have habitable life, which might cut down the total volume available by about 20%, and if one assumes (contrary to fact) that none of the supernovas are in that region, this still gives about one event every 6 billion years, so this seems to be strongly not the Filter.
There’s some reason to think that the core is unsuitable for other reasons. There are a few lines of evidence (see link below for one I could find fast) that the core of our galaxy undergoes periodic starbursts every few hundred megayears in which it has a brief episode of very concentrated rapid star formation, followed by a period of a few tens of megayears in which the supernova rate in the core temporarily exceeds the steady state galactic supernova rate by a factor of 50+. The high rate and small volume (less than 1⁄500 the galactic volume) would lead to quite the occasional local sterilization event if this does indeed happen on a regular basis.
http://www.nasa.gov/mission_pages/GLAST/news/new-structure.html