What is an essential characteristic of a neutron star?

A neutron star is formed from the remnants of a supernova, which occurs when a massive star exhausts its nuclear fuel and undergoes a catastrophic explosion, leaving behind a core that collapses under gravity. This core, if the remaining mass is sufficient, compresses to the point that protons and electrons combine to form neutrons, resulting in an incredibly dense object composed almost entirely of neutrons.

Additionally, neutron stars indeed possess a strong gravitational pull due to their compactness and the mass they contain. While their gravitational force is significant, it's important to note that the density and mass of neutron stars are responsible for their extreme properties, leading them to exert gravitational effects similar to black holes—albeit not to the extent of a black hole's event horizon.

In contrast, while some neutron stars may emit light, particularly if they are pulsars, this is not a defining characteristic of all neutron stars. Many may not emit significant light, especially if they aren't aligned in a way to be observed as pulsars. Thus, the essential characteristics of a neutron star focus on its formation from supernova remnants and its strong gravitational pull, making the collective choice that highlights both of these aspects correct.