Relativistic jet
- The lower-energy non-relativistic version of this phenomenon is described at polar jet.
Relativistic jets are extremely powerful jets[1] of plasma which emerge from presumed massive objects at the centers of some active galaxies, notably radio galaxies and quasars. Their lengths can reach several thousand[2] or even hundreds of thousands of light years.[3] The hypothesis is that the twisting of magnetic fields in the accretion disk collimates the outflow along the rotation axis of the central object, so that when conditions are suitable, a jet will emerge from each face of the accretion disk. If the jet is oriented along the line of sight to Earth, relativistic beaming will change its apparent brightness. The mechanics behind both the creation of the jets[4][5] and the composition of the jets[6] are still a matter of much debate in the scientific community; it is hypothesized that the jets are composed of an electrically neutral mixture of electrons, positrons, and protons in some proportion.
Similar jets, though on a much smaller scale, can develop around the accretion disks of neutron stars and stellar black holes. These systems are often called microquasars. A famous 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 (that is, speeds of roughly 0.99995c), making them one of the swiftest celestial objects currently known.
Rotating black hole as energy source
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 competing theories for how the energy is transferred from the black hole to the jet.
- Blandford-Znajek process.[7] This is the most popular theory for the extraction of energy from the central black hole. The magnetic fields around the 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.[8] 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,[9] and subsequently shown to be a possible mechanism for the formation of jets.[10]
Other images
See also
Further reading
References
- ^ 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?. http://www.nrao.edu/A2010/whitepapers/rac/Wehrle_AGN_jets_GCT.pdf.
- ^ Biretta, J. (1999, January 6). Hubble Detects Faster-Than-Light Motion in Galaxy M87 (http://www.stsci.edu/ftp/science/m87/m87.html)
- ^ Yale University - Office of Public Affairs (2006, June 20). Evidence for Ultra-Energetic Particles in Jet from Black Hole (http://web.archive.org/web/20080513034113/http://www.yale.edu/opa/newsr/06-06-20-01.all.html)
- ^ Meier, L. M. (2003). The Theory and Simulation of Relativistic Jet Formation: Towards a Unified Model For Micro- and Macroquasars, 2003, New Astron. Rev. , 47, 667. (http://arxiv.org/abs/astro-ph/0312048)
- ^ Semenov, V.S., Dyadechkin, S.A. and Punsly (2004, August 13). Simulations of Jets Driven by Black Hole Rotation. Science, 305, 978-980. (http://www.sciencemag.org/cgi/content/abstract/sci;305/5686/978?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=relativistic+jet&searchid=1&FIRSTINDEX=10&resourcetype=HWCIT)
- ^ Georganopoulos, M.; Kazanas, D.; Perlman, E.; Stecker, F. (2005) Bulk Comptonization of the Cosmic Microwave Background by Extragalactic Jets as a Probe of their Matter Content, The Astrophysical Journal , 625, 656. (http://arxiv.org/abs/astro-ph/0502201)
- ^ Blandford, R. D., Znajek, R. L. (1977), Monthly Notices of the Royal Astronomical Society, 179, 433
- ^ Penrose, R. (1969). Gravitational collapse: The role of general relativity. Nuovo Cimento Rivista, Numero Speciale 1, 252-276.
- ^ R.K. Williams (1995). "Extracting x rays, Ύ rays, and relativistic e−e+ pairs from supermassive Kerr black holes using the Penrose mechanism". Physical Review 51 (10): 5387–5427. doi:10.1103/PhysRevD.51.5387.
- ^ Williams, R. K. (2004, August 20). Collimated escaping vortical polar e-e+ jets intrinsically produced by rotating black holes and Penrose processes. The Astrophysical Journal, 611, 952-963. (http://arxiv.org/abs/astro-ph/0404135)