Correct Response: C. Neutron stars are the remnant stars that remain following the collapse and supernova eruption of a massive star. The majority of known neutron stars are pulsars, emitting regular and rapid radio pulses as they spin at very high speeds. Neutron stars conserve the angular momentum of the original star they formed from and because they are so small and dense, their rotational speed is very great. An expanding planetary nebula (A) would not be a likely source of rapidly pulsing radio signals from a neutron star. Black holes do emit fluctuating radio signals as they consume mass (B), but not in the regular rapid way that pulsars do. An eclipsing binary star system (D) changes brightness as one star of the pair moves in front of the other, but the regular change in brightness would be much slower than the pulses emitted by a rapidly pulsating neutron star.
