A cosmic beacon whose radiation cone rotates with unprecedented precision.
Pulsars are fast spinning neutron stars which are the extremely compact stellar remnants of stars with 8-18 solar masses. Neutron stars weigh 1-2 solar masses but are only 10 km in diameter because the neutrons are packed at maximum nuclear density. Due to their small size and lack of an energy source, Pulsars are difficult to directly observe. However, when they spin fast, Pulsars emit radiation along their poles, and that radiation hits the Earth just like the beam of a lighthouse. These pulsar beams have an extremely precise frequency and are detectable with radio telescopes. When orbiting a neutron star, general relativity predicts the two objects getting closer with time, which has been observationally confirmed.
Most known neutron stars are observed as pulsars, emitting narrow, sweeping beams of radiation. Much remains to be learned about the composition and the inner, exotic states of neutron star matter. The Neutron star Interior Composition Explorer (NICER) telescope onboard the International Space Station (ISS) measures X-ray emissions across the surfaces of neutron stars as they spin, ultimately confronting the predictions of nuclear physics theory.
Credit: NASA’s Goddard Space Flight Center.
A spinning neutron star has a powerful magnetic field whose axis intersects the north and south magnetic poles. The rotating fields generate strong electric currents and accelerate electrons, which emit an intense, narrow beam of radio radiation from each magnetic polar region. Since the magnetic field axis can be inclined to the neutron star’s rotation axis, these beams can wheel around the sky as the neutron star rotates. If one of the beams sweeps across the Earth, a bright pulse of radio emission, called a pulsar, is observed once per rotation of the neutron star.
Credit: Professor Kenneth R. Lang, 2010, Tufts University