Astrophysical jet

emitting a relativistic jet, as seen by the Hubble Space Telescope Relativistic jets are beams of ionised matter accelerated close to the speed of light. Most have been observationally associated with central black holes of some active galaxies, radio galaxies or quasars, and also by galactic stellar black holes, neutron stars or pulsars. Beam lengths may extend between several thousand, hundreds of thousands or millions of parsecs. Massive central black holes in galaxies have the most powerful jets, but their structure and behaviours are similar to those of smaller galactic neutron stars and black holes. These systems are often called microquasars and show a large range of velocities. SS 433 jet, for example, has a mean velocity of 0.26c. Relativistic jet formation may also explain observed gamma-ray bursts, which have the most relativistic jets known, being ultrarelativistic. Mechanisms behind the composition of jets remain uncertain, though some studies favour models where jets are composed of an electrically neutral mixture of nuclei, electrons, and positrons, while others are consistent with jets composed of positron–electron plasma. Trace nuclei swept up in a relativistic positron–electron jet would be expected to have extremely high energy, as these heavier nuclei should attain velocity equal to the positron and electron velocity. ==Rotation as possible energy source==

Because of the enormous amount of energy needed to launch a relativistic jet, some jets are possibly powered by spinning black holes. However, the frequency of high-energy astrophysical sources with jets suggests combinations of different mechanisms indirectly identified with the energy within the associated accretion disk and X-ray emissions from the generating source. Two early theories have been used to explain how energy can be transferred from a black hole into an astrophysical jet: • Blandford–Znajek process. This theory explains the extraction of energy from magnetic fields around an accretion disk, which are dragged and twisted by the spin of the black hole. Relativistic material is then feasibly launched by the tightening of the field lines. • Penrose mechanism. Here energy is extracted from a rotating black hole by frame dragging, which was later theoretically proven by Reva Kay Williams to be able to extract relativistic particle energy and momentum, and subsequently shown to be a possible mechanism for jet formation. This effect includes using general relativistic gravitomagnetism. ==Relativistic jets from neutron stars==

Jets may also be observed from spinning neutron stars. An example is pulsar IGR J11014-6103, which has the largest jet so far observed in the Milky Way, and whose velocity is estimated at 80% the speed of light (0.8c). X-ray observations have been obtained, but there is no detected radio signature or accretion disk. Initially, this pulsar was presumed to be rapidly spinning, but later measurements indicate the spin rate is only 15.9 Hz. Such a slow spin rate and lack of accretion material suggest the jet is neither rotation nor accretion powered, though it appears aligned with the pulsar rotation axis and perpendicular to the pulsar's true motion. ==Other images==

File:Opo0113i.jpg|Illustration of the dynamics of a proplyd, including a jet File:NGC 5128.jpg|Centaurus A in x-rays showing the relativistic jet File:Onde-radioM87.jpg|The M87 jet seen by the Very Large Array in radio frequency (the viewing field is larger and rotated with respect to the above image.) File:HST-3C66B-jet-O5BQ06010.gif|Hubble Legacy Archive Near-UV image of the relativistic jet in 3C 66B File:hs-2015-19-a-small web.jpg|Galaxy NGC 3862, an extragalactic jet of material moving at nearly the speed of light can be seen at the three o'clock position. File:Hubble Sees the Force Awakening in a Newborn Star (23807356641).jpg|Some of the jets in HH 24-26, which contains the highest concentration of jets known anywhere in the sky ==See also==