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In 1960s Jocelyn Bell, Anthony Hewish and other researchers at Cambridge University (UK) discovered a series of periodical pulses with duration of 0.3 seconds at frequency of 81.5 MHz. The discovery was made accidentally, during observations that employed radio telescope intended for the studies of space radio sources. Pulses repeated at a surprisingly precise periodic intervals equal to 1.3373011 seconds. These pulses were profoundly different from the standard chaotic picture of irregular radio frequency signals coming from space. There was even a hypothesis that an extraterrestrial civilization sends these signals to the Earth. More of the similar pulsating radio sources were discovered approximately 6 months later. Eventually, it became obvious that the sources of these signals are naturally occurring terrestrial bodies. These bodies were named pulsars.

Pulsars are presently considered to be neutron stars that were formed after outbreaks of supernovas. Pulsation constancy is a direct result of rotational stability of neutron stars. More than 1,300 pulsars in the radio region have already been discovered. An overwhelming majority of them (up to 90%) has periods with limits from 0.1 up to 1s.

If we take the period of Crab nebula pulsar as T = 0,033 c, then appropriate rotation frequency ω = 2ρ/T will be approximately equal to 200 rad/s. It follows from the second Newton's law that the average thickness of stars ρ > ω2/G. Lower limit of pulsar density equals to ρ > 6∙1014 kg/m3, which is close to substance density within atomic nuclei. Only neutron stars may be so compact and compressed to such degree, since their density is very close to the nuclear one.

The model's left-side window displays a neutron star rotating around its NS axis. Similarly to the Earth, the magnetic axis of a neutron star (designated by a green line concealed within the "tail") is inclined to its rotation axis. The system of force lines of its magnetic field rotates at a high angular velocity.

Neutrons may disintegrate into protons and electrons on the neutron star's surface. A strong magnetic field accelerates charged particles to near-sonic velocities. Particles of high energies, separated from the surface of a neutron star and accelerated by a strong electric field generate a flow passing from the neutron star and resembling solar or stellar winds. A strong magnetic field assures the flow's rotation alongside the neutron star. Moving electrons generate electromagnetic waves that are outlined in blue in the diagram. These waves are quickly rotating, which explains why the radiation of quickly rotating neutron star seems to be pulsating. In reality, the radiation is continuous, but it is neither uniform in all directions, nor isotropic. Bundles of X-rays rotate in space around the rotation axis of a neutron star, and they pass the Earth once per every period.

The observer watches pulsar flash at the moment when star radiation falls on the Earth. The section of the starry sky where a pulsar is located is in the model's lower right-hand corner. Observe the diagram of time dependence of pulsar radiation intensity in respect to the Earth.

The pulsar is depicted so close to the Earth in order to simplify the model, so that the time that it takes for the light to reach the observer would be insignificantly small. Star rotation frequency may be adjusted with the aid of a special input window.

Pulsar radiation has a non-thermal nature. It is not related to the neutron star's temperature, the amount of heat it emits, or the thermal processes on its surface.

© OpenTeach Software, 2007