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Composite Optical/X-ray image of the Crab Nebula pulsar, showing surrounding nebular gases stirred by the pulsar's magnetic field and radiation.
A pulsar, which originally stood for pulsating radio source, is a rapidly rotating neutron star, whose electromagnetic radiation is observed in regularly spaced intervals, or pulses. Pulsars are closely related to magnetars, the main difference being the strength of the object's magnetic field.
Pulsars were discovered by Jocelyn Bell and Antony Hewish in 1967 while they were using a radio array to study the scintillation of quasars. They found a very regular signal, consisting of pulses of radiation at a rate of one in every few seconds. Terrestrial origin of the signal was ruled out because the time it took the object to reappear was 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 extraterrestrial intelligence.
Thomas Gold analyzed the results of these observations, determining that the only natural object that could be responsible was a neutron star, a type of stellar object up to then only hypothesized.In the 1980s a new discovery was made, the millisecond pulsars, that, as their name indicates, instead of having periods of a few seconds, have 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 orbitFor other meanings of the term "orbit", see orbit (disambiguation In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. History Orbits were first analyseal energy of the system, which is thought to be emitted as gravitational waves.
There is general agreement that what we observe as a pulse is what happens when a beam of radiation points in our direction, once for 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 fieldIn physics, a magnetic field is an entity produced by moving electric charges ( electric currents) that exerts a force on other moving charges. The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a of the star. The beam is emitted from the poles of the neutron star's magnetic field, which may be offset from the rotational poles by a wide angle. The source of energy of the beam is the rotational energy of the neutron star, which slows down over time as the energy is emitted.
Millisecond pulsars are thought to have been spun up to high rotational speed by infalling matter pulled off of a companion star.
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 decreasing slowly but steadily, except by sudden variations. These were for a time believed to be "starquakes" due to the adjustment of the crust of the neutron star. Models where the glitch is due to a decoupling of the possibly superconductingSuperconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. In conventional superconductors, supe interior of the star have also been advanced.
In 20032003 is a common year starting on Wednesday (link will take you to calendar), and also: The International Year of Freshwater The European Disability Year Summary Perhaps the defining global event of the year 2003 was the Invasion of Iraq launched by the U observations of the Crab nebula pulsar's signal revealed "sub-pulses" within the main signal with durations of only nanoseconds. It is thought that these nanosecond pulses are emitted by regions on the pulsar's surface 60cm in diameter or smaller, making them the smallest structures outside the solar system to be measured.
As mentioned above, the discovery of pulsars allowed astronomers to study an object never observed before, the neutron star. This kind of object is the only place where the behaviour of matter at nuclearThe nucleus atomic nucleus is the center of an atom. It is composed of one or more protons and usually some neutrons as well. The number of protons in an atom's nucleus is called the atomic number, and determines which element the atom is (for example hyd density can be observed (though not directly). Also, millisecond pulsars have allowed one test of general relativityGeneral relativity (GR or general relativity theory (GRT is the theory of gravitation published by Albert Einstein in 1915. The conceptual core of general relativity, from which its other consequences largely follow, is the Principle of Equivalence which in conditions of an intense gravitational field.
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