Pulsars are rapidly rotating neutron stars that emit electromagnetic radiation and jets of particles. They are formed when a star 4-8 times the mass of the sun explodes in a supernova. Pulsars emit from two points due to their magnetic poles and are observed as light sources that turn on and off at a regular frequency. Pulsars produce magnetic fields a trillion times stronger than Earth’s and rotate between 10 and 1000 times per second, making them the most accurate clocks in the universe.
A pulsar is a rapidly rotating neutron star that emits large amounts of electromagnetic radiation (light, X-rays, radio waves, etc.) and jets of particles. A neutron star is what’s left when a star 4-8 times the mass of our sun burns off most of its fuel and explodes in a supernova. The outer layers of the star rapidly project outward as the stellar core collapses into a sphere about 20 km in diameter. Some neutron stars don’t rotate very quickly, but those that do are known as pulsars.
Suns more massive than 8 times the mass of our sun collapse to form black holes, which emit very little radiation because their gravity well is so deep that nothing can escape them. Suns less than 4 times the mass of our sun transform into red giants and then brown dwarfs, without collapsing into a neutron star. But those suns that collapse into neutron stars release enormous amounts of energy in the process, due to the sheer energy of the collapsing matter. Sometimes a small initial spin in the stellar core will greatly amplify as collapse ensues, as an ice skater tends to spin more rapidly and bring their arms closer together.
Jets of particles and electromagnetic radiation emanate from two points of the spinning neutron star: the north and south magnetic poles. Because the neutron star’s gravity is so massive (thousands of times that of the sun), very little matter or light escapes anywhere else in the pulsar. Since the magnetic poles are slightly misaligned with the axis of rotation, just like on Earth, we observe pulsars as light sources that turn on and off at a regular frequency as the magnetic poles are rotated by the rotation of the star. This phenomenon was first observed by graduate student Jocelyn Bell Burnell in late 1967.
Pulsars produce magnetic fields about a trillion times stronger than Earth’s. Pulsars in binary configurations with normal stars are the most easily observed, as all neutron stars tend to siphon matter from companion stars, resulting in a bright accretion disk. Pulsars that accumulate matter from a companion star tend to rotate even more rapidly as they gain mass. Pulsars rotate between 10 and 1000 times per second, with some variants rotating even faster. The rotational speeds of some pulsars are so regular that they are known as the most accurate clocks in the universe. Among the more exotic cosmological objects, pulsars offer us a window into a bizarre world in which high-intensity gravitational and electromagnetic fields are exposed to relativistic speeds, thus testing the very limits of our understanding of physics.
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