Pulsar

General information

The magnetic axis of a neutron star, following the example Ground, in general not being aligned perfectly with its Axis of rotation, the area of emission corresponds to a Instant given to a beam, which sweeps during time a cone because of rotation of the star. A pulsar is announced for a distant observer in the shape of a periodic signal, the period corresponding to the Period of rotation of the star. This signal is extremely stable, because the rotation of the star is also, but slows down very slightly during time.

The pulsars result from the explosion of a massive star at the end of the lifetime, phenomenon called Supernova. All the supernovas do not give rise to pulsars, some leaving behind them a Black hole, others not leaving any compact residue behind them (supernovas of the Ia type, or thermonuclear). If a neutron star has one virtually infinite lifespan, the phenomenon of emission characteristic of a pulsar occurs in general only during a few million years, after which it becomes too weak to be detectable with current technologies.

The pulsars were discovered in 1967 in a somewhat fortuitous way by Antony Hewish and its coed Jocelyn Bell (now Beautiful-Burnell Jocelyn) which studied phenomena of refractive Scintillation in the field radio and had of this fact need for an instrument measuring of the variations of a signal radio over short durations (a fraction of a second). The instrument of this fact made it possible to detect the periodic variation of objects which proved to be pulsars, the first of them bearing the name of PSR B1919+21 (or CP 1919 at the time). This discovery was rewarded by the Nobel Prize for physics, allotted in 1974 to Hewish like his/her collaborator Martin Ryle, which had built the instrument having allowed the discovery, but not to Jocelyn Bell, thing which seems today being an injustice.

The pulsars have since license the significant development of very many disciplines of the Astrophysique, energy of tests of the General relativity and the Physique of the condensed matter, until the study of the structure of the Milky Way and of course of the Supernova E. The study of a binary Pulsar, PSR B1913+16, for the first time made it possible to highlight the reality of the gravitational Rayonnement predicts by general relativity, and was also rewarded for the Nobel Prize of physics (Russell Alan Hulse and Joseph Hooton Taylor, in 1993).

Because of emission of a pulsar confined with a cone, a great number of pulsars are inobservable since the Earth, because this one is not in the cone swept by the beam of many pulsars. Nevertheless, more than 2000 pulsars are known at present (2007), it quasi totality of them being located in the Milky Way or some of its globular Amas S, the others, far from many, being located in both Nuages of Magellan. There exists a large variety of the types of pulsars (pulsars radio operator, pulsars X, abnormal pulsars X, magnétars, pulsars millisecond), whose properties depend primarily on their age and their environment.

History

The pulsars were discovered in 1967 by Jocelyn Bell and Antony Hewish with Cambridge whereas they used a Radiotélescope to study the Scintillation Quasar S. They found a signal very regular, consisted of short impulses of radiation being repeated after some second S. The terrestrial origin of the signal was excluded because time that it took to reappear was a sidereal Jour and not a solar day. This anomaly was finally identified with the signal emitted by a neutron star in fast rotation. The impulses (and are always) were emitted all the 1,3373 second S and this regularity excluded any other object.

This new object was baptized CP 19191 for Cambridge Pulsar near 19:19 m and is named today PSR 1919+21 for Pulsar with 19:19 m in Right ascension and +21° of variation . The original name for the object was “LGM”, for Little Green Men (the small green men), because the signal made think of that coming from a beacon which would have been manufactured by a extraterrestrial Intelligence. After many speculations, it was allowed that the only natural object which could be responsible for this signal was a neutron star; an object whose existence was still hypothetical.

In the Years 1980, one discovered the pulsars millisecond , which, as their name indicates it, have periods of a few milliseconds. Moreover, an important discovery was that of a pulsar in a binary system. The high precision of measurements made it possible to the astronomers to calculate the loss of orbital energy of the system, which one allots to the emission gravitational waves.

Since 1982, the B1937+21 pulsar had the highest rotational frequency and had been detected within the globular cluster Terzan 5. Its rotational frequency amounted to 642 Hz.

During the month of January 2006, a publication gave a report on the detection of a pulsar baptized Ter5ad always within the same globular cluster and whose rotational frequency amounts to 716 Hz.

Theory

It is largely allowed that the impulses which we observe are produced when a beam of radiation is directed in our direction with each rotation of neutron star. The origin of the beam is related to the non-alignment of the axis of the magnetic field of star with its axis of rotation. The beam is emitted starting from the poles of the magnetic field which can strongly deviate from the poles of rotation of star. The source of energy of the magnetic field is the energy of rotation of the star, rotation which slows down as energy is emitted.

It is thought that the high speed of rotation of the pulsars millisecond is caused by the fall of Matière torn off with a star partner.

An interesting point in the study of pulsars is the observation small irregularities number of revolutions of the neutron star. Normally, this speed decreases very slowly and very regularly, but sudden variations are observed. During a certain time, one thought that these variations were tremors of stars caused by a readjustment of the crust of star. Models where the problem is due to a decoupling of the probably superconductive interior of star were also advanced. Currently, one gives the preference to a model where these variations come from a decoupling of the superconductive heart of star.

In 2003, observations of pulsar of the Nébuleuse of the Crab revealed the existence of under-impulses one duration of a few nanoseconds superimposing itself on the principal signal. It is thought that these impulses are emitted by areas of the surface of not making pulsar more than 60 cm in diameter, which make they more the small structures outside the Solar system with being able to be measured.

Importance

As mentioned above, the discovery of pulsars made it possible to the astronomers studied an object ever observed before: the neutron star. This kind of object is the only place where one can observe, indirectly, the behavior of the matter to a Densité similar to that existing in a Atomic nucleus. Moreover, the pulsars millisecond made it possible to test the General relativity under conditions of intense Gravité.

See too

Neutron star
binary Magnétar
Pulsar
List of notable pulsars

External bonds

Astrofiles: the pulsars
to listen to the pulsars
Site of the Einstein@home project. Project of Calculation distributed using BOINC in order to detect the gravitational Radiation asymmetrical pulsar using detectors of gravitational waves

Simple: Pulsar

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