The layers in a high-mass star occur roughly in order of a. atomic number. b. decay rate. c. atomic abundance. d. spin state.

Nuclear fusion is a process where two light atomic nuclei combine to form a heavier nucleus. This fusion process releases a tremendous amount of energy, which powers stars. In high-mass stars, nuclear fusion occurs in a sequence of layers.

In the core, extreme temperatures and pressures allow hydrogen to fuse into helium. As the star evolves, the helium burns into carbon and oxygen in a shell surrounding the core. This multi-layered fusion continues, forming heavier elements like neon, magnesium, and silicon in successive outer shells.

The energy generated from these fusion reactions counteracts gravity, maintaining the star's structure. Without nuclear fusion, stars would collapse under their gravity.

The atomic number of an element is the number of protons present in the nucleus of its atoms. This number uniquely identifies each element and determines its position in the periodic table.

In high-mass stars, the arrangement of layers based on elements directly ties to the atomic number. At the center are elements with higher atomic numbers, such as iron (atomic number 26), and towards the surface, we find elements with lower atomic numbers, like hydrogen (atomic number 1).

The star's core contains heavy elements due to the immense pressure and temperature required for fusion, whereas lighter elements are pushed outwards.

The stellar structure of a high-mass star is characterized by its layers, each responsible for fusing different elements. These layers result from the varying temperatures and pressures needed for different fusion reactions.

Starting from the core:

• The central core is where heavy elements like iron are found. Here, nuclear fusion has produced the highest atomic number elements.
• Surrounding the core, there are shells where fusion continues for elements with progressively lower atomic numbers as we move outward.
• Finally, the outermost layers consist mainly of lighter elements like hydrogen and helium.

This layered shell structure is vital in understanding the lifecycle and evolution model of high-mass stars. Each layer's fusion process releases energy needed to balance the gravitational forces trying to collapse the star.