“Here I trying to get a Ph.D. out of a new technique, and some silly lot of little green men had to choose my aerial and my frequency to communicate with us.”
Jocelyn Bell Burnell said that years later about the strangest few weeks of her graduate research, and it captures the mood exactly. She wasn’t hoping to discover anything cosmic. She was a doctoral student at Cambridge, and for nearly two years before the discovery she had helped physically build the instrument that would make it, an array designed by her supervisor, Antony Hewish, covering roughly four acres of Cambridgeshire farmland with more than 4,000 dipole antennas strung between wooden posts, built to catch distant quasars by the way their signal flickers as it passes through the solar wind.
By 1967 her job had shifted to running a hundred feet of chart paper through her hands every few days, looking for anything unusual in the noise. What she found instead was a signal too perfectly regular to be a natural object, at least by everything astronomers thought they knew at the time.
A signal ticking too perfectly to be a star
The signal showed up as what Bell Burnell called a bit of “scruff” on the chart, a faint, repeating mark she noticed only because she had spent months learning what the ordinary noise looked like. Once she pointed the telescope back at that same patch of sky, the source ticked out pulses one and a third seconds apart, over and over, with a regularity nothing in the sky was supposed to have.
Stars flicker. Galaxies vary slowly. Nothing natural known in 1967 kept a beat that clean. She and her supervisor, Antony Hewish, only half-joking, labeled the source LGM-1, for little green men, on the chart itself, because writing out its actual coordinates every time felt absurd. “It was easier than saying ‘you know that funny pulsing source at right ascension 1919, declination plus 20’. So, it became LGM,” she said of the shorthand.
We put together an entire video about a much stranger version of the same basic question, whether an unexplained signal from deep space means something is out there or nothing at all. It follows a completely different discovery, decades later and involving a completely different kind of instrument, but it opens on the exact same kind of static nobody could explain at first.
How the little green men hypothesis died
The joke lasted only until Bell Burnell found a second, completely different ticking signal elsewhere in the sky, on an unrelated patch of chart paper from a different part of her survey. “It finally scotched the little green men hypothesis,” she explained decades later, “because it’s highly unlikely there’s two lots of little green men, on opposite sides of the universe, both deciding to signal to a rather inconspicuous planet, Earth, at the same time, using a daft technique and a rather commonplace frequency.”
What she and Hewish had actually found was a pulsar, the compressed core left behind after a massive star collapses in a supernova, spinning many times a second and sweeping a beam of radio waves past Earth once every rotation, the way a lighthouse sweeps its beam across a coastline.
Hewish shared the 1974 Nobel Prize in Physics for the discovery with fellow astronomer Martin Ryle. Bell Burnell, the student who actually spotted the scruff and ran down what it was, was left off the prize, a decision that stayed controversial in astronomy for decades. She has said the omission bothered her contemporaries more than it bothered her.
A ticking star and a silent gas, sharing only the doubt that came first
It matters to be honest about how different these two discoveries actually are underneath the surface similarity. A pulsar is a specific, physical object, a city-sized ball of neutron-degenerate matter with a magnetic field strong enough to fire a genuine, directional beam of radio waves at precise mechanical intervals.
The tone in the video above has no object behind it at all, no beam, no rotation, no source anyone can point a telescope at. It comes from warm, ordinary interstellar gas oscillating in place, broadband and continuous rather than a sharp, ticking pulse. One is arguably one of the most extreme physical objects in the universe. The other is closer to the universe’s version of background room tone.
What actually connects the two stories is the process, not the physics: the same discipline of ruling out the exciting explanation before accepting the boring one, and the same discomfort of not knowing, for a while, whether a signal means something is broadcasting or whether something ordinary just happens to hum.
Bell Burnell had to rule out an alien civilization before she was allowed to believe in a dead star. Decades later, the scientists reading Voyager’s plasma data had to rule out something out there generating the tone before they could accept that nothing was, that warmth alone was enough.
Both answers turned out to be less dramatic than the first guess and somehow more remarkable for it. A dead star spinning fast enough to sweep a lighthouse beam across an entire galaxy’s width of space, and a thin gas simply humming at its own natural temperature, sit at opposite ends of what deep space can produce, one an object so extreme it briefly seemed to need an intelligence behind it, the other so ordinary it took decades before anyone thought to check if it was there at all.
Between those two ends is most of what makes listening to space worth doing in the first place, the plain fact that you cannot know in advance which kind of silence you have found until you have ruled out every other kind.
