One day, an astronomer student found something strange in her radio astronomy data. A very weak blip coming from one part of the sky that repeated every 1.3 seconds with incredible precision. She and her supervisor immediately figured that it was impossible for a message from aliens, but how else to explain such an astoundingly regular signal from space.

Other two astronomers developed their experiments to catch up with the theorical explanation. By looking at the discovery of the sub-atomic particle called the neutron, they suggested that when an old large star runs out of nuclear fuel, it rapidly collapses under its own gravity. The star’s core suddenly transforms into a super dense ball of neutrons, and the outer layers of the star bounce off in a massive explosion of light and energy, a supernova. The dense core of neutrons that remains behind, forms a neutron star, would have the mass of two or three suns squeezed down into the size of a large city.

When a star suddenly collapses like this, two interesting things can happen. The star typically rotate like once every few days. The law of conservation of angular momentum suggests that when a star collapses the rotation speeds up. In case of neutron stars, it could spin at an incredible speed of ten or even hundreds of times a second. Like the Earth, a star has magnetic field and takes this incredibly intense field upon collapse. Charged particles in the super-hot plasma surrounding a neutron star would get funneled towards the stars magnetic poles and shot out into space as two intense beams like a lighthouse. Because the rotation axis is not aligned with the magnetic axis, what astronomers receive on Earth is the radio emission at a specific frequency.