Black Widow Pulsar
A Black Widow, Eng. Black Widow Pulsar, describes in astronomy a millisecond pulsar with a low-mass companion in a close orbit. The electromagnetic and particle radiation of the pulsar heat the surface of his companion and lead within a few million years to complete evaporation of the companion star. Through the circumstellar matter around the companion star, the pulses of the neutron star for up to 40 % of the web orbital period are attenuated. Due to this change, the light cover black widow spiders are also called Eclipsing Binary Millisecond Pulsars (English for eclipsing Millisekundenpulsare in binary systems ).
Properties
The Black Widows are Millisekundenpulsare with the shortest known pulse periods with values of less than five milliseconds. Since the pulsars gain the energy to the electromagnetic radiation from its rotation speed, the Black Widows are likely to be very young Millisekundenpulsare. The web orbital period of the binary system is of the order of one day. Among the pulsars, the magnetic flux density of the black widows of 108 Gauss is very low. The proper motion of this Millisekundenpulsare is high with values of a few 100 km / s and they therefore belong to the high-speed engines. The high escape velocity is likely to be a consequence of the formation of the pulsar in a supernova. Because of the rapid proper motion they are often in high galactic latitudes.
The companion is brighter on its side facing the pulsar due to the heating by the incident on its surface radiation. For PSR B1957 20, the surface temperature of the companion is on the night side at 2900 K, while the sunlit dayside from the pulsar reaches a temperature of 8300 K. In H -alpha is indicative of a shock front due to the pulsar show. In the field of X-ray radiation is reflected not only a point source, a mist along the moving direction of the black widow. The fog is made of material that has been removed from the companion star remains.
Of several black widows pulsed gamma rays have been observed so far. Since the gamma rays can be detected throughout all phases of railway circulation, they can not arise through an interaction with circumstellar matter around the companion. Rather, they should be in the magnetic field of the neutron star that emits directly by the Pulsarmechanismus, the acceleration of charged particles. It is therefore possible that there is a significantly larger number of binary systems of a millisecond pulsar and a faint degenerate companion are as yet unknown, since the radio emission is absorbed by the circumstellar matter or pulsars are generally radio quiet.
The mass of the neutron star in the black widows is two to three solar masses. These values are direct measurements using the Shapiro delay and derived from the path dynamics of the binary system. Probably the neutron stars are born with a mass of 1.4 solar mass and accrete the rest of their companions over a period of three billion years ago.
Development
Black Widow arise, for example in low-mass X-ray binaries. The neutron stars are after her birth in a supernova a normal pulsar and consume their rotational energy through the emission of electromagnetic radiation, until they reach a rotation period of a few seconds. The companion star expands in the course of its development, because the hydrogen supply is exhausted in its core or the web running time is reduced due to a torque loss by a stellar wind along the magnetic field lines. Thus, the companion exceeds the Roche limit volume and matter transfer from the companion star to the neutron star begins. With the power and torque over a matter accretion disk is transferred to the neutron star, which is much faster and showing its rotation period decreases again. In the phase of mass accretion, the binary system is observed as a Röntgenpulsar. The matter falls along the magnetic field lines onto the magnetic poles of the neutron star and sets braking energy in the form of intense X-ray radiation. Due to the rotation of the neutron star, the magnetic poles are periodically visible and there is a pulsed X-ray radiation in the direction of the earth. The accreting millisecond pulsar SWIFT J1749.4 -2807 is observed in the present phase. If the rotational energy is sufficient again to turn on the Pulsar, the radiation is incident from the pulsar the companion star and the binary star system shows all the signs of a black widow.
Redbacks
If the companion red dwarfs, so one speaks also of Redback (English for Rotrücken, named after spiders). An example of such a constellation is PSR J1023 0038. Redbacks be interpreted as an intermediate stage shortly after the reactivation of the pulsar. In the final stage, a large proportion of the companion has already been removed, while the red dwarfs in the Redbacks still have a hydrogen-rich atmosphere. In the year 2001 showed optical spectra of PSR J1023 0038 nor emission lines from the accretion disk around the neutron star, which can not be detected since 2004. It is not clear whether evolve Redbacks in Black Widow or already represent the final stage of development of these close binary systems.
Examples
- PSR B1957 20
- PSR B1744 -24A