Read an Academic Passage

In 1967, a graduate student named Jocelyn Bell Burnell was analyzing data from a radio telescope she had helped construct when she noticed an unusual, highly regular signal pulsing roughly once every 1.3 seconds. The signal was so precise and rhythmic that Bell Burnell and her supervisor, Antony Hewish, briefly and half-jokingly labeled it "LGM-1," short for "Little Green Men," wondering whether they had accidentally detected a transmission from an extraterrestrial civilization. Further investigation soon revealed additional signals of a similar nature coming from other locations in the sky, effectively ruling out the possibility that the original signal had been an artificial transmission aimed specifically at Earth.

The signals were eventually identified as coming from a previously unknown type of astronomical object, later named a pulsar. Pulsars are a specific type of rapidly rotating neutron star, the extraordinarily dense remnant left behind after a massive star collapses in a supernova explosion. A neutron star packs roughly the mass of the sun into a sphere often no larger than a mid-sized city, resulting in gravitational and magnetic forces of extraordinary intensity. As a pulsar rotates, it emits focused beams of radio waves from its magnetic poles, and if one of these beams happens to sweep across Earth during each rotation, astronomers detect it as a regular pulse, much like the periodic flash of a lighthouse beam sweeping across the ocean.

The discovery of pulsars proved valuable for reasons that extended well beyond confirming their existence as a new class of object. [A] Because pulsars rotate with extraordinary precision, some maintaining timing accuracy comparable to atomic clocks, astronomers realized they could serve as natural tools for testing fundamental physics. [B] Researchers have used the precise timing of pulsar signals to detect subtle distortions in spacetime predicted by Einstein's theory of general relativity. [C] Arrays of pulsars distributed across the galaxy are now being used in ongoing efforts to detect gravitational waves too large and slow to be captured by ground-based detectors. [D] Bell Burnell's initial discovery, once mistaken for an alien signal, ultimately opened an entirely new branch of observational astrophysics.