Astrophysical jet

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An astrophysical jet (hereafter 'jet') is a phenomenon often seen in astronomy, where streams of matter are emitted along the axis of rotation of a compact object. While it is still the subject of ongoing research to understand how jets are formed and powered, the two most often proposed origins are dynamic interactions within the accretion disk, or a process associated with the compact central object (such as a black hole or neutron star). When matter is emitted at speeds approaching the speed of light, these jets are called relativistic jets, because the effects of special relativity become important. The largest jets are those from black holes in active galaxies such as quasars and radio galaxies. Other systems which often contain jets include cataclysmic variable stars, X-ray binaries and T Tauri stars. Herbig–Haro objects are caused by the interaction of jets with the interstellar medium. Bipolar outflows or jets may also be associated with protostars (young, forming stars),[1] or with evolved post-AGB stars (often in the form of bipolar nebulae).

Question dropshade.png Unsolved problem in physics:
Why do the disks surrounding certain objects, such as the centers of active galaxies, emit jets along their polar axes?
(more unsolved problems in physics)

Accretion disks around many stellar objects are able to produce jets, although those from super massive black holes are generally the fastest and most active. It has been theorized the speed of a jet is about the same as the escape velocity of the central object. While it is not known exactly how accretion disks would accelerate jets or produce positron-electron plasma, they are generally thought to generate tangled magnetic fields that cause the jets to accelerate and collimate. The hydrodynamics of a de Laval nozzle may also give a hint to the mechanisms involved.

Occurrence of jets[edit]

Jets, or more generally bipolar outflows, are also surprisingly common. They have been studied in association with active galactic nuclei (AGN), binary X-ray sources, young stellar objects, novae and so on. Jet speeds are typically a few times the escape velocity from the central object; in the case of black holes, bulk Lorentz factors of γ ∼ 10 are inferred. (Gamma ray bursts may also produce jets with Lorentz factors γ ∼ 300.) Jets are so common that it has been speculated that they may be an essential concomitant of accretion flow – the channels through which the liberated angular momentum and perhaps also much of the energy leave the system. The challenge to the astrophysicist is to explain how jets are powered and collimated. However, even after decades of work, major theoretical and observational questions about their origin and collimation still remain.[2]

Relativistic jets[edit]

Relativistic jet. The environment around the AGN where the relativistic plasma is collimated into jets which escape along the pole of the supermassive black hole.

Relativistic jets are very powerful jets[3] of plasma, with speeds close to the speed of light, that are emitted near the central black holes of some active galaxies (notably radio galaxies and quasars), stellar black holes, and neutron stars. Their lengths can reach several thousand[4] or even hundreds of thousands of light years.[5] If the jet speed is close to the speed of light, the effects of the Special Theory of Relativity are significant; for example, relativistic beaming will change the apparent beam brightness (see the 'one-sided' jets below). The mechanics behind both the creation of the jets[6][7] and the composition of the jets[8] are still a matter of much debate in the scientific community. Jet composition might vary; some studies favour a model in which the jets are composed of an electrically neutral mixture of nuclei, electrons, and positrons, while others are consistent with a jet primarily of positron-electron plasma.[9][10]

Elliptical galaxy M87 emitting a relativistic jet, as seen by the Hubble Space Telescope.

Massive galactic central black holes have the most powerful jets. Similar jets on a much smaller scale develop from neutron stars and stellar black holes. These systems are often called microquasars. An example is SS433, whose well-observed jet has a velocity of 0.23c, although other microquasars appear to have much higher (but less well measured) jet velocities. Even weaker and less relativistic jets may be associated with many binary systems; the acceleration mechanism for these jets may be similar to the magnetic reconnection processes observed in the Earth's magnetosphere and the solar wind.

The general hypothesis among astrophysicists is that the formation of relativistic jets is the key to explaining the production of gamma-ray bursts. These jets have Lorentz factors of ~100 or greater (that is, speeds over roughly 0.99995c), making them some of the swiftest celestial objects currently known.

Jet composition[edit]

One of the best observational approaches to investigate the mechanisms which produce jets is to determine the jet composition at radii where they can be observed directly. In the case of black-hole jets, the plasma is likely to be electron-ion if the jet originates from a disk, or positron-electron if it derives from the black hole.[11] Multiple recent measurements indicate initial relativistic jet composition is primarily positron-electron plasma.[12][13]

Trace nuclei swept up in a relativistic positron-electron jet would have extremely high energy, as these heavier nuclei would have a velocity equal the relativistic positron and electron velocity.

Lab production of 5MeV positron-electron beams allows study of characteristics such as the shock effect of GRBs and how different particles interact with and within relativistic positron-electron beams (for example how beam positrons and electrons combine).[14]

Rotating black hole as possible energy source[edit]

Because of the enormous amount of energy needed to launch a relativistic jet, some jets are thought to be powered by spinning black holes. There are two well known theories for how energy is transferred from a black hole to a jet.

  • Blandford–Znajek process.[15] This is the most popular theory for the extraction of energy from a central black hole. The magnetic fields around an accretion disk are dragged by the spin of the black hole. The relativistic material is possibly launched by the tightening of the field lines.
  • Penrose mechanism.[16] This extracts energy from a rotating black hole by frame dragging. This theory was later proven to be able to extract relativistic particle energy and momentum,[17] and subsequently shown to be a possible mechanism for the formation of jets.[18]

Jets from neutron stars[edit]

The pulsar IGR J11014-6103 with supernova remnant origin, nebula and jet.

Jets may also be observed from neutron stars, an example being the pulsar IGR J11014-6103, which produces the largest jet observed in the Milky Way Galaxy. This jet is observed in x-rays and has no detected radio signature.[19] As neutron stars do not have an event horizon, they (like protostellar jets) cannot be powered by processes like those discussed in the previous section.[20] Some theories suggest the neutron star magnetic field powers the jets and the rotation of this intense magnetic field generates intense electric fields that literally tear electrons from the star surface to form the jets.[21]

IGR J11014-6103 has an estimated jet velocity of 0.8c. It is not listed in the latest revision of Accreting Millisecond X-Ray Pulsars (AMXPs)[22] and no accretion material has been detected.[23][24][25][26] This star was presumed to be rapidly spinning but later measurements indicate the spin rate is only 15.9 Hz.[27][28] This rather slow spin rate and lack of accretion material suggest this 0.8c positron-electron jet is neither rotation nor accretion powered. In the image the JET, aligned with the pulsar rotation axis, is perpendicular to the pulsar's trajectory and extends out over 37 light years (about 10 times the distance from our sun to the nearest visible star). This distance is quite impressive considering the estimated star's mass/radius is about 2M/12-km, an illustration of the power of relativistic jets. Interestingly, large clouds of positron-electron plasma are sometimes observed near ordinary (non-runaway) neutron stars that have no jets.[29]

Other images[edit]

See also[edit]

References[edit]

  1. ^ "Star sheds via reverse whirlpool". Astronomy.com. 27 December 2007. Retrieved 26 May 2015. 
  2. ^ https://arxiv.org/pdf/astro-ph/0107228v1.pdf Blandford Roger,Compact Objects and Accretion Disks
  3. ^ Wehrle, A.E.; Zacharias, N.; Johnston, K.; et al. (11 Feb 2009). "What is the structure of Relativistic Jets in AGN on Scales of Light Days?" (PDF). Astro2010: the Astronomy and Astrophysics Decadal Survey. 2010: 310. Bibcode:2009astro2010S.310W. 
  4. ^ Biretta, J. (6 Jan 1999). "Hubble Detects Faster-Than-Light Motion in Galaxy M87". 
  5. ^ "Evidence for Ultra-Energetic Particles in Jet from Black Hole". Yale University – Office of Public Affairs. 20 June 2006. Archived from the original on 2008. 
  6. ^ Meier, David L (2003). "The theory and simulation of relativistic jet formation: Towards a unified model for micro- and macroquasars". New Astronomy Reviews. 47 (6–7): 667. arXiv:astro-ph/0312048free to read. Bibcode:2003NewAR..47..667M. doi:10.1016/S1387-6473(03)00120-9. 
  7. ^ Semenov, V.; Dyadechkin, Sergey; Punsly, Brian (2004). "Simulations of Jets Driven by Black Hole Rotation". Science. 305 (5686): 978–980. arXiv:astro-ph/0408371free to read. Bibcode:2004Sci...305..978S. doi:10.1126/science.1100638. PMID 15310894. 
  8. ^ Georganopoulos, Markos; Kazanas, Demosthenes; Perlman, Eric; Stecker, Floyd W. (2005). "Bulk Comptonization of the Cosmic Microwave Background by Extragalactic Jets as a Probe of Their Matter Content". The Astrophysical Journal. 625 (2): 656. arXiv:astro-ph/0502201free to read. Bibcode:2005ApJ...625..656G. doi:10.1086/429558. 
  9. ^ Wardle, J.F.C (1998). "Electron–positron jets associated with the quasar 3C279". Nature. 395 (1 October 1998): 457–461. Bibcode:1998Natur.395..457W. doi:10.1038/26675. 
  10. ^ "NASA – Vast Cloud of Antimatter Traced to Binary Stars". 
  11. ^ https://arxiv.org/pdf/astro-ph/0107228v1.pdf Blandford Roger,Compact Objects and Accretion Disks
  12. ^ Electron-positron Jets Associated with Quasar 3C 279
  13. ^ https://www.youtube.com/watch?v=Sw-og52UUVg Science With Integral, Sep 2008 (start four minutes into video, note Sagittarius produces 15 billion tons/sec of positron-electron matter)
  14. ^ Lab production of 5MeV positron-electron beams
  15. ^ Blandford, R. D.; Znajek, R. L. (1977). "Electromagnetic extraction of energy from Kerr black holes". Monthly Notices of the Royal Astronomical Society. 179 (3): 433. Bibcode:1977MNRAS.179..433B. doi:10.1093/mnras/179.3.433. 
  16. ^ Penrose, Roger (1969). "Gravitational Collapse: The Role of General Relativity". Rivista del Nuovo Cimento. 1: 252–276. Bibcode:1969NCimR...1..252P.  Reprinted in: Penrose, R. (2002), ""Golden Oldie": Gravitational Collapse: The Role of General Relativity", General Relativity and Gravitation, 34 (7): 1141, Bibcode:2002GReGr..34.1141P, doi:10.1023/A:1016578408204 
  17. ^ R.K. Williams (1995). "Extracting x rays, Ύ rays, and relativistic ee+ pairs from supermassive Kerr black holes using the Penrose mechanism". Physical Review. 51 (10): 5387–5427. Bibcode:1995PhRvD..51.5387W. doi:10.1103/PhysRevD.51.5387. PMID 10018300. 
  18. ^ Williams, Reva Kay (2004). "Collimated Escaping Vortical Polar e−e+Jets Intrinsically Produced by Rotating Black Holes and Penrose Processes". The Astrophysical Journal. 611 (2): 952. arXiv:astro-ph/0404135free to read. Bibcode:2004ApJ...611..952W. doi:10.1086/422304. 
  19. ^ "Runaway pulsar has astronomers scratching their heads". 
  20. ^ "Neutron Star Fires Powerful Jets". 
  21. ^ "Crab Nebula's Neutron Star Pulsed Most Powerful Beam Ever Detected --". The Daily Galaxy --Great Discoveries Channel: Sci, Space, Tech. 
  22. ^ Patruno, A.; Watts, A. L. (2012). "Accreting Millisecond X-Ray Pulsars". arXiv:1206.2727free to read [astro-ph.HE]. 
  23. ^ "Fastest Pulsar Moving With Tremendous Speed Of 6 Million Miles Per Hour – Found – MessageToEagle.com". 
  24. ^ "Chandra :: Photo Album :: IGR J11014-6103  :: June 28, 2012". 
  25. ^ Pavan, L.; Pühlhofer, G.; Bordas, P.; Audard, M.; Balbo, M.; Bozzo, E.; Eckert, D.; Ferrigno, C.; Filipović, M. D.; Verdugo, M.; Walter, R. (2015). "A closer view of the IGR J11014-6103 outflows". arXiv:1511.01944free to read [astro-ph.HE]. 
  26. ^ "Neutron star jet: An exploded star creates a truly bizarre scene.". Slate Magazine. 
  27. ^ Pavan, L.; Bordas, P.; Pühlhofer, G.; Filipović, M. D.; De Horta, A.; o' Brien, A.; Balbo, M.; Walter, R.; Bozzo, E.; Ferrigno, C.; Crawford, E.; Stella, L. (2014). "The long helical jet of the Lighthouse nebula, IGR J11014-6103" (PDF). Astronomy & Astrophysics. 562: A122. arXiv:1309.6792free to read. Bibcode:2014A&A...562A.122P. doi:10.1051/0004-6361/201322588.  Long helical jet of Lighthouse nebula page 7
  28. ^ Halpern, J. P.; Tomsick, J. A.; Gotthelf, E. V.; Camilo, F.; Ng, C. -Y.; Bodaghee, A.; Rodriguez, J.; Chaty, S.; Rahoui, F. (2014). "Discovery of X-ray Pulsations from the INTEGRAL Source IGR J11014-6103". The Astrophysical Journal. 795 (2): L27. arXiv:1410.2332free to read. Bibcode:2014ApJ...795L..27H. doi:10.1088/2041-8205/795/2/L27. 
  29. ^ https://www.youtube.com/watch?v=Sw-og52UUVg Science With Integral, Sep 2008 (start four minutes into video, note Sagittarius produces 15 billion tons/sec of positron-electron matter)
  30. ^ "Hubble Video Shows Shock Collision Inside Black Hole Jet". 27 May 2015. 

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