Pulsar - the neutrone star.
Pulsars (short from Pulsating Sources of Radioemission) are the space sources of radioemission and of electromagnetic radiation, discovered in 1967 by E. Hewish group (Great Britain).
After loosing its energy sources the star begins to freeze and compress. Its physical properties are greatly changed. So its pressure is increasing. If the star mass is small the gravitation forces are weak and the star compression (the gravitational collapse) is stopped. In other case it is continued. At the high density the electrons, connecting with protons, form the neutral particles - neutrons. Soon nearly all the star consists of neutrons so compressed that the great star mass sphere with some kilometers radius and the compression stopped.
The density of this sphere - the neutron star - is fantastically great even comparing the so-called white dwarfs, it is above 10 mln t/sm^3.
The existence of the neutron stars was predicted by the soviet physician Lev Davidovich Landaw. And in 1934 Walter Baad and Fritz Twikky worked in the USA supported that these stars are the fragments of supernew stars. Naturally after the discovery of pulsar connection with the remains of the supernew star outbursts it was supposed that the pulsars and the neutron stars are the same objects.
How do the pulsars emit the electromagnet waves? At the star compression not only its density increases.
According to the low of conservation of momentum during the star radius decreasing the velocity of rotation increases. While the collapse of the great massive star to the size of some tens kilometers the period of rotation decreases to hundred and even thousand parts of a second, i.e. to the proper periods of the star also becomes more dense.
In the external layer of a neutron star, where the substance dense is not so great to break the cores; they may from the hard chip structure, which at the pulsar rotation decreasing is broken the starquake.
The discovery of pulsar was very important not only for astronomy but for physics too. The emitting of pulsar help to investigate the properties of the powerful gravitational and magnetic fields, that is impossible in the terrestrial conditions. Changing while passing through the interstar gas, the pulsar emitting carries the important tack information about the composition and physical properties of the interstar medium.