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Linking Mass Extinctions To the Sun's Journey In the Milky Way
schwit1 writes "In a paper published today on the Los Alamos astro-ph preprint service, astronomers propose that as many as eleven past extinction events can be linked to the Sun's passage through the spiral arms of the Milky Way. (You can download the paper here [pdf].) From the paper: 'A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy's various spiral arms.'"
http://news.nationalgeographic.com/news/2007/04/070420-extinctions.html Other researchers found that time periods Earth is exposed to large amounts of cosmic rays is correlated with mass extinction events. This is a possible explanation.
We are actually passing through a minor one right now, called the Orion Spur.
http://en.wikipedia.org/wiki/File:Artist's_impression_of_the_Milky_Way_(updated_-_annotated).jpg
No mention of Shock waves, or even a hint of what might cause such shock, or how such shock could be transmitted in the vacuum of space.
Via the interstellar medium, of course. It's pretty tenuous, but most certainly is capable of sustaining phenomena like shock waves. Which isn't to say that that's necessarily the particular process that is dominant in the galactic arms; it could also be something relating to magnetism, as the physics of a flowing magnetically-coupled medium is viciously difficult to work with (i.e., highly non-linear). And I've got no idea what happens at the phase change boundaries between the parts of the ISM which are plasmas and the parts which are conventional (tenuous) gasses; phase changes can do "interesting" things.
As for what's powering it all, you've got some exceptionally powerful energy sources out there. Black holes in particular can pump vast amounts of energy into the surrounding volume of space. The stellar wind from very high mass stars would be another interesting source.
"Little does he know, but there is no 'I' in 'Idiot'!"