Pulsars are highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation. As they spin, these beams sweep across space, and if aligned with Earth, they can be detected as regular pulses of radio waves. This regularity makes pulsars useful for various scientific applications, including testing theories of gravity. Discovered in 1967 by Jocelyn Bell Burnell and Antony Hewish, pulsars are remnants of massive stars that have undergone supernova explosions. Their rapid rotation and strong magnetic fields result from the collapse of the star's core, leading to incredibly dense objects, often just about 20 kilometers in diameter.