Answer: Pulsars are collapsed stars that are rotating.
Explanation:
When a massive star collapses at the end of its journey, it either forms a neutron star or a black-hole. A pulsar is a rotating neutron star. It is highly magnetized. It emits electromagnetic radiation. It emits small bursts of radio waves periodically. These are detected by the radio telescopes from Earth.
Thus, the correct answer is: Pulsars are collapsed stars that are rotating.