Pulsar

A pulsar, which originally standed for pulsating radiosource, is a rapidly rotating neutron star, whose electromagnetic radiation is observed in regularly spaced interval, or pulses.

History

Pulsars where discovered by [Jocelyn Bell]? and [Antony Hewish]? on 1967. They were using a radio array to study the scintillation of quasars. They found a very regular signal, consisting of pulses of radiation of a few seconds. Terrestial origin of the signal was ruled out by the time it took the object to reappear, a [sidereal day]? instead of a [solar day]?. The original name for the object was "LGM", Little Green Men, thinking of it as a beacon made by some extraterrestial intelligence. After more speculation, an agreement was reached that the only natural object that could be responsible was a neutron star, a kind of object up to then only hypotesized.

In the 80's a new discovering was made, of millisecond pulsars, that, as their name indicates, instead of having periods of a few seconds, ahve periods of a few milliseconds.

Also important was the discovery of a pulsar in a binary system. The high precision of the measurements allowed astronomers to calculate the loss of orbital energy of the system, that is thought to be emitted as [gravitational wave]?s.

Theory

There is general agreement that what we observe as a pulse is what happens when a beam of radiation points in our direction, once every rotation of the neutron star. The origin of the beam is related to the misalignment of the rotation axis and the axis of the magnetic field of the star. The source of energy of the beam is the rotational energy of the neutron star, that slows down.

Of interest to the study of the state of the matter in a neutron stars are the glitches observed in the rotation velocity of the neutron star. This velocity is slowing down steadily, except by sudden by sudden variations