Neutron stars are the collapsed cores left behind when a star more massive than about 8 Suns ends its life in a core-collapse supernova. Gravity crushes roughly 1.4 solar masses into a sphere only about 10-12 km in radius, producing densities near 4x10^17 kg/m^3 -- a single sugar-cube's worth of that material would weigh around a billion tons on Earth. Because angular momentum is conserved as the core shrinks, the star spins up dramatically, and its magnetic field is compressed to enormous strength. A pulsar is a neutron star whose magnetic poles (often misaligned with its spin axis) emit beams of radiation that sweep across space like a lighthouse as the star rotates, producing regular pulses when a beam crosses Earth's line of sight. When a pulsar has a companion star, it can pull gas from it into a swirling, superheated accretion disk that spirals inward before falling onto or launching off the star.

• Typical neutron star mass: ~1.4 solar masses packed into a ~10-12 km radius
• Density: roughly 4x10^17 kg/m^3, comparable to an atomic nucleus
• Spin periods range from milliseconds to several seconds; fastest known is PSR J1748-2446ad at ~716 Hz (716 rotations per second)
• Surface magnetic fields: ~10^8-10^15 Gauss, with magnetars at the extreme high end
• First pulsar discovered in 1967 by Jocelyn Bell Burnell, initially nicknamed "LGM-1" (Little Green Men)
• Radiation beams emerge along the magnetic axis, which can be tilted relative to the rotation axis
• Accretion disks form when a pulsar's gravity strips gas from a nearby companion star
• Formed from core-collapse supernovae of progenitor stars exceeding ~8 solar masses