Chapter 17, Problem 1QP

To determine

The reason why the interior of an evolved high-mass stars has layers like those of an onion.

Answer to Problem 1QP

Options (c).

Explanation of Solution

High-mass stars are stars with masses greater than about eight times mass of the Sun. As a high-mass star evolves, it builds up a layered structure like that of an onion, with progressively more advanced stages of nuclear fusion found deeper and deeper within the star.

As the high-mass star leaves the main sequence, the core will begin to collapse and the carbon fusion will occur. Carbon fusion will produce more massive elements including oxygen, sodium, neon and magnesium. The star then will have a carbon fusing core surrounded by a helium-fusing shell surrounded by a hydrogen-fusing shell, which moves outward as fusion products accumulate in the core. When carbon is exhausted as a nuclear fuel at the center of the star, neon breaks down to oxygen and helium or fuses to magnesium; and when neon is exhausted, oxygen begins to fuse. Thus, the residue of one reaction becomes the fuel for the next as the star evolves a layered structure like that of onion.

Conclusion:

Since a high-mass star develops a layered structure as a result of the heavier atoms fuse closer to the center because the high pressure and temperature available there, option (c) is correct.