Black widow (astronomy)
A black widow , Eng. Black Widow Pulsar , describes in astronomy a millisecond pulsar with a low-mass companion in a narrow orbit. The electromagnetic and particle radiation of the pulsar heat the surface of its companion and lead to the complete evaporation of the companion star within a few million years. Due to the circumstellar matter around the companion star, the pulses of the neutron star are attenuated for up to 40% of the orbital period. Because of this eclipsing change the black widow spiders are also called Eclipsing Binary Millisecond pulsars (Engl. For eclipsing millisecond pulsars in binary systems ), respectively.
properties
The black widows are millisecond pulsars with the shortest known pulse periods with values of less than five milliseconds . Since the pulsars obtain the energy for the electromagnetic radiation from their speed of rotation, the black widows are likely to be very young millisecond pulsars. The orbit duration of the double system is in the order of one day. Among the pulsars, the magnetic flux density of the black widows of 10 kT (10 8 Gauss ) is comparatively very low. The intrinsic movement of these millisecond pulsars is high with values of a few 100 km / s and thus they belong to the fast runners . The high escape speed is likely a consequence of the formation of the pulsar in a supernova . Because of their fast proper motion, they are often in high galactic latitudes.
The companion is brighter on the side facing the pulsar due to the heating from the radiation hitting its surface. At PSR B1957 + 20 in the constellation Arrow, the surface temperature of the companion, a brown dwarf, on the night side is 2900 K. The day side illuminated by the pulsar is heated to 8300 K. The H-alpha shows signs of a shock front due to the pulsar radiation. In the X-ray range , next to a point source, there is a plasma nebula along the movement direction of the black widow made of material from the companion star.
The pulsar's radio light penetrates this mist of electrically conductive gas. Instead of weakening this radiation, the nebula amplifies pulsar pulses at some frequencies up to 80 times in millionths of a second just before and after the pulsar is covered by the densest part of the nebula. The differences in density in the fog act on radio waves like glass lenses on light: if the radio waves, which are directed in different ways, overlap, the radio pulse has 80 times more energy. Due to time and frequency-dependent fluctuations in the radiation, its origin was determined to an accuracy of around 10,000 meters in the magnetosphere surrounding the pulsar. Over 6,500 light years away, that's the thickness of a hair on Mars from Earth.
This resolution, previously thought to be unimaginable, represents a record in radio astronomy.
Pulsed gamma rays have been observed by several black widows . Since this radiation can be detected over all phases of the orbit, it cannot arise through interactions with circumstellar matter around the companion. It should be emitted directly by the pulsar mechanism, through the acceleration of charged particles in the magnetic field of the neutron star. Possibly there are considerably more binary star systems consisting of a millisecond pulsar and a faint degenerate companion than previously known, because the radio radiation is absorbed by the surrounding matter or the pulsars are radio-calm.
The mass of the neutron stars in black widows is two to three solar masses. These values are direct measurements with the help of the Shapiro delay and derived from the orbital dynamics of the binary star system. The neutron stars probably form with a mass of 1.4 solar mass and suck in the rest of the companion for up to three billion years.
development
Black widows, for example, arise in low-mass X - ray binary stars . After their birth in a supernova, neutron stars are normal pulsars and use up their rotational energy by emitting electromagnetic radiation until they rotate for a few seconds. The companion star expands in the course of its development because the hydrogen supply in its core has been used up or the travel time is reduced due to a loss of torque caused by a stellar wind along its magnetic field lines. As a result, the companion exceeds the Roche limit volume and a transfer of matter from the companion star to the neutron star begins. With the flow of matter, torque is also transmitted via an accretion disk to the neutron star, which is accelerated and its period of rotation decreases again. In the phase of mass accretion , the binary star system is observed as an X-ray pulsar. The matter falls along the magnetic field lines onto the magnetic poles of the neutron star and releases braking energy in the form of intense X-rays. Due to the rotation of the neutron star, the magnetic poles become periodically visible and a pulsed X-ray radiation is generated in the direction of the earth. The accreting millisecond pulsar SWIFT J1749.4–2807 is being observed in this phase. When the rotational energy is again sufficient to turn the pulsar on, the radiation from the pulsar hits the companion star and the binary star system shows all signs of a black widow.
Redbacks
If the companion red dwarfs , so we also speak of Redback (Engl. For Rotrücken , named after spinning ). An example of such a constellation is PSR J1023 + 0038 . Redbacks are interpreted as an intermediate stage shortly after the reactivation of the pulsar radiation. 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 2001, optical spectra from PSR J1023 + 0038 still showed emission lines from the accretion disk around the neutron star, which have not been detectable since 2004. It is not clear whether redbacks will evolve into black widows or whether they are already the final stages of the evolution of these close binary star systems.
Examples
- PSR B1957 + 20
- PSR B1744−24A
Web links
Individual evidence
- ↑ RHH Huang, AKH Kong, J. Takata, CY Hui, LCC Lin, KS Cheng: X-ray studies of the Black Widow Pulsar PSR B1957 + 20 . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1209.5871 .
- ↑ W. Bednarek and J. Sitarek: High energy emission from the nebula around the Black Widow binary system Containing millisecond pulsar B1957 + 20 . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1212.6394 .
- ^ Mallory SE Roberts: New Black Widows and Redbacks in the Galactic Field . In: Astrophysics. Solar and Stellar Astrophysics . 2011.
- ↑ FAZ.net Jan Hattenbach: Deadly Dance of the Black Widow June 1, 2018
- ^ HJ Pletsch: Binary Millisecond Pulsar Discovery via Gamma-Ray Pulsations . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1211.1385 .
- ^ JE Horvath, OG Benvenuto: Is There a Crisis in Neutron Star Physics? In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1307.1832v1 .
- ↑ D. Altamirano et al .: Discovery of an accreting millisecond pulsar in the eclipsing binary system Swift J1749.4-2807 . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1005.3527 .
- ↑ Mallory SE Roberts: Surrounded by spiders! New black widows and redbacks in the Galactic field . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1210.6903 .
- ↑ PR Breton et al .: DISCOVERY OF THE OPTICAL COUNTERPARTS TO FOUR ENERGETIC FERMI MILLISECOND PULSARS . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1302.1790v1 .