A surprising "pre-discovery" —

That time an Air Force sergeant spotted pulsars months before astronomers

Jocelyn Bell-Burnell: "He happened to be a very observant person."

Pulsars are spinning neutron stars, the relics of massive stars gone supernova.
Enlarge / Pulsars are spinning neutron stars, the relics of massive stars gone supernova.
NASA's Goddard Space Flight Center

Here's a bit of science history that genuinely surprised many of us here at Ars Technica. We all know the famous story of how Jocelyn Bell-Burnell discovered pulsars in 1967 as a graduate student at the University of Cambridge—and the longstanding debate about whether she should have shared the Nobel Prize awarded to her supervisor, Antony Hewish. But apparently, an Air Force staff sergeant manning an early warning radar station in Alaska arguably beat Bell-Burnell to the punch. He just couldn't come forward until 2007, after the instrument had been decommissioned. Nature reported the story at the time, but we most definitely missed it—and we probably weren't the only ones.

Pulsars are rapidly spinning neutron stars that create pulsed emissions as their magnetic fields sweep across the line of sight with Earth. As previously reported, whenever a massive star runs out of fuel, it explodes into a supernova. If it's above a certain threshold in mass, it becomes a black hole. Below that threshold, it becomes an ultra-dense neutron star. Pulsars are unusual in that they spin rapidly and have very powerful magnetic fields, so they emit very high-energy beams of light. The star's rotation makes it seem like those beams are flashing on and off like a cosmic lighthouse.

Bell-Burnell was monitoring the new radio telescope at the Mullard Radio Astronomy Observatory, sifting through reams and reams of paper records to hunt for any unusual anomalies in the peaks of data representing incoming galactic radio waves. Three weeks in, on August 6, she spotted a faint signal coming from a particular area of the sky that disappeared, then reappeared, in 1.34-second intervals. The team quickly ruled out any known natural sources or other kinds of interference. She and Hewish even joked that it might be a signal from an alien civilization, dubbing the object "LGM-1" for "Little Green Men."

Then, just before Christmas, Bell-Burnell spotted another signal coming from a different part of the sky, this time arriving every 1.25 seconds. She found two more signals right after the holiday, also from different parts of the sky. Clearly, this was a new type of star, not aliens. She and Hewish dubbed them "pulsars." Everyone recognized that this was a momentous discovery. By the end of 1968, astronomers had discovered dozens more pulsars, and the discovery gave them an invaluable new tool for exploring the universe—most recently detecting the "hum" of the universe's gravitational wave background. There are now more than 1,000 known pulsars.

The "bit of scruff" was actually a new kind of rotating neutron star.
Enlarge / The "bit of scruff" was actually a new kind of rotating neutron star.
National Radio Astronomy Observatory

Unbeknownst to astronomers, earlier that same year, an Air Force sergeant named Charles Schisler had noticed a faint signal on his radar scope at the Clear Air Force Station in Alaska. It kept reappearing, week after week, throughout the summer. One day, he noted that the blip appeared four minutes earlier than the day before. Schisler had been a B-47 navigator and correctly concluded that the blip must be some kind of star since he knew that stars rise four minutes earlier each night as the Earth orbits the Sun.

Schisler was able to calculate the approximate position of the signal's source in the sky—the Crab Nebula—and even shared his discovery with an astronomer at the University of Alaska at Fairbanks. Schisler went on to record about a dozen radio sources likely to be pulsars, although he admitted he had no idea what he'd observed until he heard the news about the official discovery. "He happened to be a very observant person," Bell-Burnell told Nature in 2007. Unfortunately, that information was classified, and Schisler wasn't able to reveal his work until the Clear station was decommissioned.

According to Bell-Burnell, there were others besides Schisler who spotted evidence of pulsars without realizing that they might be significant—including a woman visiting the University of Chicago's observatory in the 1950s, who mentioned a pulsing signal of light emanating from the Crab Nebula. Astronomers dismissed the woman's story. None of this changes the significance of Bell-Burnell and Hewitt's accomplishment since they were the first to conclude that they were observing coherent pulses—the telltale signature of a radio pulsar. But it would still have been useful observational data for astronomers. "I wish we had had a way to communicate with the scientific community," Schisler told Nature.

Channel Ars Technica