by iamlucky13 » Wed Dec 06, 2006 1:27 am
I hope I'm understanding the question right. If not, I apologize.
The area behind the bow wave is actually relatively free of matter, due to the solar wind and radiation pressure pushing free gas and dust outward. At the edge of the heliopause, the outward pressure from the sun is approximately equal to the, shall we say, ambient pressure of the surrounding gas. Charged particles entering this region are slowed by encountering extrasolar particles. As they lose kinetic energy, the emit photons. So not only is there less matter to warm and emit or reflect radiation behind the bow shock, but the solar wind is just streaming through without emitting either, until it encounters the instellar gas. A little more info:
http://en.wikipedia.org/wiki/Solar_syst ... st_regions
As far as the extreme size of the bubble: Alpha Cam is a blue-white supergiant. One of the links from the APOD states that it has an intensity 530,000 times as great as our sun. For comparison, our sun's bow shock occurs about 230 AU's out, which is ~0.004 light years. The intensity of radiation drops off with the distance squared (an area relation). By my math, to achieve the equivalent pressure at 10 light years, our sun would have to be a frightening 7 million times brighter, assuming all other factors are equal.
This number sounds a little high to me (I'm fairly confident in my back of the napkin math), but it gets down to about a factor of 10, and I'm not sure I accounted right for the kinetic energy of stellar wind particles. It's also possible that the interstellar medium is more dense in our region than around Alpha Cam, and likely that Alpha Cam has a disproportionately intense stellar wind (note that it is 530,000 times more intense, but only 30 times more massive).
I admit I'm pushing some of my knowledge a little. I welcome any nitpicks others might have.
I hope I'm understanding the question right. If not, I apologize.
The area behind the bow wave is actually relatively free of matter, due to the solar wind and radiation pressure pushing free gas and dust outward. At the edge of the heliopause, the outward pressure from the sun is approximately equal to the, shall we say, ambient pressure of the surrounding gas. Charged particles entering this region are slowed by encountering extrasolar particles. As they lose kinetic energy, the emit photons. So not only is there less matter to warm and emit or reflect radiation behind the bow shock, but the solar wind is just streaming through without emitting either, until it encounters the instellar gas. A little more info:
http://en.wikipedia.org/wiki/Solar_system#Farthest_regions
As far as the extreme size of the bubble: Alpha Cam is a blue-white supergiant. One of the links from the APOD states that it has an intensity 530,000 times as great as our sun. For comparison, our sun's bow shock occurs about 230 AU's out, which is ~0.004 light years. The intensity of radiation drops off with the distance squared (an area relation). By my math, to achieve the equivalent pressure at 10 light years, our sun would have to be a frightening 7 million times brighter, assuming all other factors are equal.
This number sounds a little high to me (I'm fairly confident in my back of the napkin math), but it gets down to about a factor of 10, and I'm not sure I accounted right for the kinetic energy of stellar wind particles. It's also possible that the interstellar medium is more dense in our region than around Alpha Cam, and likely that Alpha Cam has a disproportionately intense stellar wind (note that it is 530,000 times more intense, but only 30 times more massive).
I admit I'm pushing some of my knowledge a little. I welcome any nitpicks others might have.