Final answer:
After helium fusion ends in a low-mass star, it is unable to continue fusion into heavier elements. It will expand, shed its outer layers, and form a planetary nebula with a white dwarf as its remnant core.
Step-by-step explanation:
Once a low-mass star has completed the helium core and shell fusion stages, it undergoes a significant transformation. After depleting helium in the core, the star undergoes a contraction. This contraction heats up a shell of helium, which begins to fuse and forms a new energy source.
However, once this helium is exhausted, the star does not have enough mass to continue to higher stages of nuclear fusion, such as fusing carbon into heavier elements.
The subsequent layers above the core, including a shell where hydrogen has reached temperatures sufficient for helium fusion, contribute to multi-layered internal structure. The planetary nebula is formed when the star's outer layers are ejected, and the exposed hot inner layers are set aglow by the ultraviolet radiation from the dying star.
This glowing gas is what we see when we observe a planetary nebula. Eventually, the remnant core left behind will cool and shrink into a white dwarf, marking the final stage in the life cycle of a low-mass star.
Therefore, the correct answer to what happens to the surface of a low-mass star after the helium core and shell fusion stages are completed is: C) The star is propelled slowly away from the core to form a planetary nebula.