Jocelyn Bell Burnell arrived at the University of Cambridge in themid-nineteen-sixties, just as construction was beginning on a new kindof radio telescope. For two years, as she worked on her doctorate inastronomy, she helped string wires between wooden poles, until four and a half acres of field were woven in copper filament andcable. “I came of a family that did a lot of sailing, so it wasn’ttotally alien,” Bell Burnell told me recently. “I was used to posts andmasts and pulleys.”
By July, 1967, the telescope was ready. It resembled a giant metal net.Within a few weeks, its antennae had caught something unusual. BellBurnell—who analyzed the roughly seven hundred feet of paper generatedeach week as galactic radio waves were recorded in inked peaks—noticed afaint signal arriving from one slice of sky. Then it disappeared. InNovember, she saw it again. By adjusting the speed of the recordingdevice, she determined that the signal came in every 1.34 seconds, aregular beat against the background static of the cosmos. Bell Burnellpuzzled with her adviser, Antony Hewish, about whether it was of thisworld—an Earthly radio station, perhaps—or of another. They gave it thefanciful nickname of L.G.M.-1, for “little green men.”
Just before Christmas, on a morning so cold that Bell Burnell had tobreathe on the recording equipment to warm it to working temperature,she found a second signal in another part of the sky. This one arrivedevery 1.25 seconds. Soon after the holidays, she spotted two more. Eachof the four rhythmic waves originated in a different sector of theuniverse, effectively ruling out actual L.G.M. as the source. The firstsignal became, instead, CP 1919—“CP” for “Cambridge pulsar,” and “1919”for the star’s celestial location in hours and minutes. A new era ofcosmology opened.
Pulsars are closely related to black holes. Both are born when a massivestar runs out of fuel: its outer layers explode in a supernova, and itscore collapses. The star’s original mass determines what happens next.If the core was more massive than about three of Earth’s suns, it turnsinto a black hole; if not, the pressure and density of the collapse,which fuse electrons and protons into neutrons, produce a neutron star.Pulsars, a subset of these dead stars, spin at immense speeds and havepowerful magnetic fields that accelerate nearby electrons, lashing theminto beams of electromagnetic radiation. Because the stars rotate, thosebeams—which can be radio waves, gamma- or X rays, or visiblelight—appear, to a distant observer, to flash on and off. Pulsars areoften called cosmic lighthouses.
The existence of both neutron stars and black holes was predicted in thenineteen-thirties, and the discovery of pulsars—identified as a type ofneutron star soon after CP 1919 was reported—suggested that black holesmust be out there, too. The first confirmed black hole was reported afew years later. Pulsars “meant that a lot of this kind of crazy theorythat had been kicking around since Einstein dropped the general theoryof relativity on us, that maybe it was real,” Stephen Eikenberry, aprofessor of astronomy at the University of Florida, told me. “Think ofit this way: people were asking us to believe in fairies and elves. Butthen, when you meet an elf, fairies seem like not such a crazy idea.”
Because of their enormous density and precise, clock-like rotation,pulsars provided a new way to probe space and theory. “These fifty yearshave been amazingly exciting, with a lot of totally unexpected newdiscoveries in connection with pulsars rolling in,” Bell Burnell,currently a visiting professor in physics at the University of Oxford,said. Even the first pulsar’s disappearance, between August andNovember, 1967, supplied useful information. Interference frominterstellar material, it turned out, made the radio waves seem totwinkle on and off. “At the time this was happening, we didn’t know thatthere was stuff between the stars, let alone that it was turbulent,”Bell Burnell said. “That is one of the things that has come out of thediscovery of pulsars—more knowledge about the space between the stars.”Close observation of a pulsar and the space around it led to the firstconfirmedexoplanets—planetsorbiting other suns, of interest in the search for extraterrestriallife. Pulsars also helped catalyze the hunt for gravitationalwaves,wrinkles in the substance of space-time. The most recent detection, thisfall, recorded the disruption caused by merging neutron stars.
Observations under way around the world promise more insights courtesyof pulsars. “They turned out to be much more extreme objects than we hadimagined could exist,” Bell Burnell said. “Because they are extreme,they tell us a lot about the extremes of physics, the extremes ofnature.” Their extreme mass, for instance, offers scientists a way tobetter understand Einstein’s general theory ofrelativity.The stronger the gravitational force, the more clear the effects ofrelativity, Eikenberry said. He is one of many astronomers who hope forthe discovery of a pulsar orbiting a black hole, since the tick of thepulsar’s clock could perhaps be seen slowing in thrall of a black hole’smass. Pulsars could also reveal information about the feasibility of aninterstellar navigation system; their regular signals could serve aslandmarks by which to triangulate a spacecraft’s position. Yet, for allthey illuminate, pulsars themselves remain shadowy. The detailed physicsof their emissions is still not well understood. “We are using thoseflashes of light to tell us all kinds of very cool things,” Eikenberrysaid. “But we don’t know how those flashes of light actually happen, howpulsars shine.”
Bell Burnell did not study pulsars after her doctoral work. Sheperformed other astrophysical research, advocated for women in science,and led institutions including, recently, the Royal Society ofEdinburgh. Marriage and motherhood led to a peripatetic, part-timeacademic life and, consequently, an eclectic curriculum vitae, she said.In 1974, Hewish, Bell Burnell’s former adviser, was awarded the NobelPrize in Physics for a discovery that the committee described as “ofparamount importance to physics and astrophysics.” Hewish had aco-recipient, but it wasn’t BellBurnell—afact that many observers have attributed to her gender. Bell Burnell hasrepeatedly noted that Nobels do not generally go to graduate students,and that the committee did not know that she was a woman. But manyfamiliar with the story, and with pulsars’ far-ranging legacy, seeinjustice. “It is just such a clear example of the difference for womenand anyone who is not on the top,” Matthew Stanley, a historian ofscience at New York University, said. “The whole subaltern communitysuffers in not getting credit for the work that they have done.”
Bell Burnell’s observations during those chilly winter days and nights,signals captured by wires looped across hoary fields, eventually foundtheir way back to the universe that had sent them. In the seventies, NASA launched four space probes to explore the outer solar system. Eachwas outfitted with a map, which used fourteen pulsars to identify oursun’s relative position in the galaxy—the hope being that an alienmight one day encounter the probes and find its way to Earth. “It was the first time we were actuallythinking that something that could be made by humans could leave thesolar system,” Keith Gendreau, of NASA’s Neutron Star InteriorComposition Explorer mission, said. “This kind of crystallized theexcitement of the time, of real exploration, of going out there.” Of thepossibility of L.G.M. Though neutron stars rotate more slowly as theysenesce, the maps ought to be decipherable to intelligent life well intothe future. “It would be a little bit of a math problem, but totallysolvable,” Gendreau said.
The steady beats of the first four pulsars have become part of a vastpercussive array. More than two thousand others—superfast “millisecond”pulsars, slow pulsars, solitary pulsars, pulsars living in pairs—havenow been found. As Bell Burnell wrote just a few years after herdiscovery, “these incredible stars continue to puzzle, and occasionallyto surprise.”
