November 28, 1967 - Mullard Radio Astronomy Observatory near Cambridge. Jocelyn Bell and her supervisor Antony Hewish identify signals, which they initially dismissed as radio interference, as a series of pulses, evenly spaced every 1.33 seconds.
Not long after the discovery, rumors started to bubble up. Was some form of extraterrestrial intelligence trying to reach us? Sending signals in hopes of a chance to communicate, not knowing that we don’t possess the technology to decode them?
On December 21, not even a month after the discovery of the first pulsar, Jocelyn Bell discovered another series of pulses, coming from another place in the galaxy, thus ruling out the possibility of signals from extraterrestrial intelligence.
Pulsars, which look a bit like stars that get turned on and off every second, used to be stars more massive than the sun before they turned into pulsars. When stars this massive burn out all their fuel, they collapse into so-called neutron stars. The death of stars often creates an explosion, called a supernova. The neutron star is the material that remains after an explosive death like this. Even though neutron stars are smaller than the stars they came from, they’re not small at all. The typical size of a neutron star can be anything from 20 to 24 kilometers and they can have up to twice the mass of the sun. That means that, according to NASA, a sugar-cube-sized bit of a neutron star would weigh about 1 billion tons, that’s around the weight of Mount Everest, for reference.
But why do they pulse?
Pulsars don’t actually pulse; the name is a bit misleading. What looks like pulsing is the beam of radiation created in the magnetic field of the neutron star. Neutron stars are smaller than they were before they collapsed, so the angular speed increases. The magnetic axis is not aligned with the axis of rotation so its periodic oscillation results in the emission of radiation. The rotation is why we can only see those beams of radiation when they sweep through Earth’s line of sight.
Similar to a lighthouse, they stay blinking in our universe. And while we can’t use them to navigate our way around the cosmos, they are still a big part of research in Astronomy and Astrophysics, helping us measure distances or functioning as the most accurate natural clocks in the universe.