means A rapidly rotating neutron star that emits regular beams of radiation, detected on Earth as precise, repeating pulses.

from A 1960s blend of 'pulse' and the '-ar' ending borrowed from 'quasar.' When the first one was found in 1967, its signal was so metronomically regular that astronomers half-jokingly tagged it LGM-1 — 'Little Green Men' — wondering if it was a beacon. It wasn't aliens, just a spinning stellar corpse, but the name 'pulsating star,' clipped to 'pulsar,' stuck. 'Pulse' itself traces back through Latin 'pulsus,' from 'pellere,' to beat or drive — the same root that gives us 'pulse' in your wrist.