What is a pulsar in astronomy


A pulsar is a rotating neutron star, its axis of rotationNot coincides with the magnetic field axis, so that a double cone (Biconus) emitted radiation rotates with the rotation period of the star like a lighthouse. In special cases this radiation can hit the earth, which gives the observer the impression of pulsed radiation. In the illustration above, the pulsar's axis of rotation is black, while the axis of the magnetic field is shown in red. The red lines illustrate that Pulsar magnetosphere in the form of isocontour lines of the magnetic field: One recognizes a dominant toroidal (tube-like) magnetic field structure, which results from the high rotation and the gravitomagnetic forces (gravitomagnetic dynamo). The green structures illustrate the radiation lobes that repeatedly hit a suitably oriented observer as a result of the rotation.

Origin of pulsar light

The radiation is synchrotron radiation, which is produced by relativistically fast elementary particles (electrons and positrons, also protons and ions) in the high magnetic fields of the pulsed magnetosphere.

fast rotation ...

Since the angular momentum is almost retained even in gravitational collapse, the neutron star takes over the angular momentum of the precursor star. progenitor). It must be taken into account that the star core typically rotates decoupled from outer star shells and 'rotates away from under the star's surface'. According to this, only the angular momentum of the star nucleus is transferred to the emerging neutron star. The neutron star as a representative of the class compact objects however, it is much more compact, so that the rotation speed is many times higher than that of the forerunner star ('pirouette effect'). The fastest pulsars therefore rotate around themselves in the order of milliseconds (ms)! your name is Millisecond pulsars.

... is braked

However, the rotational energy of the rapidly rotating pulsar is reduced over time. It feeds the magnetic fields and electromagnetic radiation that the pulsar emits. The magnetic fields are strengthened by the gravitomagnetic dynamo, which is at the expense of the rotation. For this reason, the measured rotation period or the deceleration rate of the pulsar provides information about the strength of the magnetic field and the pulsar age. Millisecond pulsars are therefore young pulsars.

Discovery, frequency, magnetic field

The first pulsar was discovered in 1967 and was a radio pulsar. Astronomers currently know more than 1700 pulsars. Of these, about 170 are millisecond pulsars, about 130 are in binary star systems. Does the pulsar have a particularly high magnetic field from around 1014 Gauss, that's what they call him Magnetar.

Crab - an optical pulsar

The Crab pulsar is located in the Crab Nebula in the constellation bull (see observation photo above; large version; Credit: NASA / ESA / HST, Hester & Loll 2005). It is a Supernova remnant (Supernovaremnant, SNR) at a distance of approx. 6500 light years. The picture shows a unique wealth of structures in the explosion area. In the center, the relativistic electrons that were accelerated in the Crab Nebula glow blue and diffuse. The supernova (Type II) that led to this neutron star was observed by Chinese astronomers in 1054. Back then, the supernova's light curve was visible to the naked eye for several weeks or even months! The nebula was formed by ejected gas carried out by the supernova explosion. Today astronomers still observe gas expansion at a speed of about 1000 km / s. In the center of the Crab Nebula was a optical millisecond pulsar discovered! The rotation time is only 33 ms, which is why the associated neutron star with the designation NP 0532 is one of the fastest pulsars that have been discovered.