Pulsar, << PUHL sahr, >> is an object in space from which regular bursts of electromagnetic radiation are received on Earth. Most of this radiation takes the form of radio waves. Pulsars received their name from these highly regular pulses.
Scientists believe pulsars are rapidly spinning neutron stars. Neutron stars are dense stars composed primarily of tightly packed neutrons, or perhaps of elementary particles called quarks. An extremely powerful magnetic field surrounds the neutron star and rotates with it. This rapidly rotating magnetic field produces a strong electric field. The electric field rips electrons and protons from the star’s surface. As these particles flow from the star, they emit (give off) energy in the form of a narrow beam of radio waves. The beam rotates as the star spins. Using a radio telescope, an astronomer can detect a pulse of radio waves each time the pulsar rotates so that the beam sweeps past Earth.
On the average, radio pulsars spin at the rate of two rotations per second. All radio pulsars eventually lose energy and slow down. They do so in such a predictable manner that their pulses can be used to measure time.
The strong gravity of a pulsar can capture gases from a nearby companion star. These gases crash into the pulsar, creating hot spots that send out beams of X rays. Some pulsars gain momentum and rotate faster as they capture gases from companion stars. These pulsars, called millisecond pulsars, rotate hundreds of times per second. Scientists believe many millisecond pulsars occur in high concentrations of stars known as globular clusters (see Star cluster).
Astronomers study pulsars to learn about globular clusters. They also learn about the matter between stars by studying how this matter affects the radiation coming from pulsars. Other studies search for changes in the timing of certain pulsar’s bursts. These changes may be evidence of gravitational waves produced in the early universe (see Gravitational wave). Scientists also study how pulsars convert rotational energy into radio beams.
Radio pulsars were discovered in 1967 by the British astronomers Jocelyn Bell (later Bell Burnell) and Antony Hewish. In 1992, the Polish astronomer Alexander Wolszczan announced evidence that three planets are orbiting a pulsar called PSR B1257 + 12. These planets were the first to be discovered outside the solar system. See Exoplanet.
In 1979, astronomers observed high-energy bursts from a new type of pulsar. These pulsars, now called magnetars, can have magnetic fields more than 1,000 times stronger than those of typical pulsars. Magnetars emit pulses of X rays and gamma rays as they rotate. In magnetars, it is the strength of the magnetic field, and not its rotation, that powers the beams of energy. The strong magnetic fields may also cause magnetars occasionally to emit second-long bursts of energy that can be greater than the total energy that the sun gives off over several hundred thousand years.
In 2013, scientists announced the discovery of a pulsar that alternated between X-ray and radio wave emissions. The changes in emission are from 30 minutes to 6 hours apart.
In 2014, scientists studying X-ray sources discovered a pulsar emitting light 100 times more energetic than possible under the current understanding of pulsars. The pulsar, designated M82 X-2, has a rotational period of 1.37 seconds and gives off a pulse with as much energy as 10 million suns.
