Jocelyn Bell Burnell noticed a "bit of scruff" in data from a radio telescope, which turned out to be from PSR B1919+21, the first discovered pulsar.

Dame Susan Jocelyn Bell Burnell is a Northern Irish physicist who, while conducting research for her doctorate, discovered the first radio pulsars in 1967. This discovery later earned the Nobel Prize in Physics in 1974, but she was not among the awardees.

A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum, just as optical telescopes are used to make observations in the visible portion of the spectrum in traditional optical astronomy. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

PSR B1919+21 is a pulsar with a period of 1.3373 seconds and a pulse width of 0.04 seconds. Discovered by Jocelyn Bell Burnell on 28 November 1967, it is the first discovered radio pulsar. The power and regularity of the signals were briefly thought to resemble an extraterrestrial beacon, leading the source to be nicknamed LGM, later LGM-1.

A pulsar is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays.