Which celestial structure is often seen as the dense center of an aged star?

The dense center of an aged star is best represented by a white dwarf. When a star like our sun exhausts its nuclear fuel, it undergoes a series of transformations leading to the shedding of its outer layers, resulting in the formation of a planetary nebula. What remains at the core is the white dwarf, which is composed primarily of carbon and oxygen.

A white dwarf is the remnant of a star that has completed its life cycle and no longer undergoes fusion reactions, leading to it being extremely dense. This density arises because it still contains a significant amount of mass, but all of that mass is compressed into a relatively small volume. As such, a white dwarf typically has a mass comparable to that of the sun, but it is only about the size of Earth.

The other options represent different stages or types of stars. A neutron star is a more extreme remnant of a massive star that has gone through a supernova explosion, while a red supergiant is an evolved star in a much later stage before it potentially explodes as a supernova. A planetary nebula refers to the shell of gas expelled by a star like the sun, which can be seen surrounding the white dwarf but is not the dense remnant itself. Thus