Time That Star!

Pulsars and Neutron Stars

Some stars emit X-rays in a very rapid regular, periodic pattern. These objects are called X-ray pulsars. Pulsars are spinning neutron stars, and a neutron star is the superdense remains of an exploded star that gravitationally collapsed back in on itself to form a small, compressed core of neutrons. When a neutron star is in a binary system with a sun-like star, matter can be gravitationally pulled off the stellar companion, and in the process, X-rays are emitted.

More specifically, pulsars have jets of particles moving at the speed of light streaming out of their two magnetic poles. These jets produce very powerful beams of light. We know that on Earth, the spin axis (true north) is not the same as the magnetic axis. This is also seen in X-ray pulsars. Because of this, the beam of light from the jet sweeps around as the pulsar rotates, like the spotlight in a lighthouse does. As a ship in the ocean that sees only regular flashes of light from a lighthouse, we on Earth see pulsars turn on and off as the beam sweeps over the Earth.

How much mass the star had when it died determines what it becomes. Stars about the same size as the Sun become white dwarfs, which glow from leftover heat. Stars that have about 8-20 times that of our Sun collapse into neutron stars. And a star with mass more than about 20 times the Sun's gets crushed into a single point, which we call a black hole.

Watch the video below for further explanation and visualizations of how a pulsar works.