Fifty-two years ago today, Cambridge graduate student Jocelyn Bell was examining paper strip charts of cosmic radio emissions when she noticed a peculiarity. A source in the constellation of Vulpecula, the Fox (roughly midway between the three brightest stars currently high in the western sky around 7 p.m.) was pulsating regularly, unlike any known radio source. Bell’s “bit of scruff” was the emission of the first known neutron star, a bizarrely compact stellar corpse. Its discovery garnered Bell’s thesis adviser the 1974 Nobel Prize in physics.
Sun-like stars resist gravity with gas pressure (the repulsion between particles of like electrical charge). When stars run out of nuclear fuel, gravity collapses their cores until maximum gas pressure is exceeded. Their skyrocketing density is eventually stabilized by the Pauli Exclusion Principle, a property of the quantum realm that prevents identical particles (electrons, in this case) from occupying the same space.
More massive stars’ gravity can overwhelm the Exclusion Principle, fusing electrons and protons into neutrons (the reverse of a type of nuclear decay). Further collapse is halted when the Exclusion Principle prevents the neutrons from occupying the same space, producing a neutron star: roughly two solar masses crammed into a few-miles-wide sphere with a density of billions of tons per teaspoon.
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Such extreme collapse results in terrific rotation, like a star-sized ice skater pulling herself into a city-sized ball, until she’s spinning hundreds of times per second. If its rotating emission region sweeps our way, we see a “pulsar” (a regularly pulsing radio source). Bell’s pulsar is relatively old, having slowed to a leisurely one spin per 1.3 seconds.
Since 1967, more than 2,000 pulsars have been found. Last year, Bell was honored with a $3 million prize, which she donated to assist women, minority, and refugee physics students.
Next column: Planetary photobombs.