Rick's Cosmology Tutorial: Chapter 19 Abstract

In Chapter 18 a solar model was presented based on the polytropic-hydrostatic equation. This model did not constrain the rate of nuclear heat production to balance against the rate of heat transport. In this Chapter we derive the opacity required, as a function of radius, in order for this heat balance to hold. This is based on the assumption that the heat transport is by radiation. The resulting opacities are in reasonable, if crude, agreement with opacities obtained from the literature, at least within the region which is radiation dominated. At larger radii, where heat transport is probably by convection, the effective opacities from our model of Chapter 18 are, not surprisingly, too small. This merely compensates for the neglect of the convective mechanism. This result illustrates that a complete solar model would need a reasonably good convective model to produce reliable results.

The opacities within the central, radiation dominated, region are considerably greater than those due to hydrogen alone (as derived in Chapter 16). I have not established the reason for this. I assume it must be due to the 'metal' content of the sun (i.e. elements beyond helium). This Chapter is incomplete due to this issue being currently unresolved.

The Helix Nebula (NGC7293) in Aquarius. This is one of the largest planetary nebula and the closet to earth at an estimated distance of 450 ly. It is very large, its outer shell extends to nearly the diameter of the full moon.