[[File:ESO Centaurus A LABOCA.jpg|thumb|The [[starburst galaxy]] [[Centaurus A]], with its plasma jets extending over a million [[Light-year|light years]], is considered as the closest [[Active galactic nucleus|active]] [[radio galaxy]] to [[Earth]]. The 870-micron [[Submillimetre astronomy|submillimetre]] data, from [[Atacama Pathfinder Experiment|LABOCA]] on APEX, are shown in orange. [[X-ray]] data from the [[Chandra X-ray Observatory]] are shown in [[blue]]. [[Light|Visible light]] data from the [[MPG/ESO telescope|Wide Field Imager]] (WFI) on the MPG/ESO 2.2 m telescope located at [[La Silla Observatory|La Silla, Chile]], show the background [[star]]s and the galaxy's characteristic [[dust lane]] in close to "true colour".]]
[[File:ESO Centaurus A LABOCA.jpg|thumb|The [[starburst galaxy]] [[Centaurus A]], with its plasma jets extending over a million [[Light-year|light years]], is considered as the closest [[Active galactic nucleus|active]] [[radio galaxy]] to [[Earth]]. The 870-micron [[Submillimetre astronomy|submillimetre]] data, from [[Atacama Pathfinder Experiment|LABOCA]] on APEX, are shown in orange. [[X-ray]] data from the [[Chandra X-ray Observatory]] are shown in [[blue]]. [[Light|Visible light]] data from the [[MPG/ESO telescope|Wide Field Imager]] (WFI) on the MPG/ESO 2.2 m telescope located at [[La Silla Observatory|La Silla, Chile]], show the background [[star]]s and the galaxy's characteristic [[dust lane]] in close to "true colour".]]
An '''astrophysical jet''' is an [[astronomy|astronomical]] phenomenon where [[Ionization|ionised]] matter is expelled at high velocity from an astronomical object, in a pair of narrow streams aligned with the object's [[rotation|axis of rotation]].<ref>
}}</ref> When the matter in the beam approaches the [[speed of light]], astrophysical jets become '''relativistic jets''' as they show effects from [[special relativity]].
Astrophysical jets are associated with many types of [[High-energy astronomy|high-energy astronomical sources]], such as [[black hole]]s, [[neutron star]]s and [[pulsar]]s. Their causes are not yet fully understood, but they are believed to arise from dynamic interactions within [[accretion disk]]s. One explanation is that as an accretion disk spins, it generates a rotating, tangled [[magnetic field]] which concentrates material from the disk into the jets and then drives it away from the central object.<ref name="Kundt">{{cite journal
|last=Kundt |first=W.
|year=2014
|title=A Uniform Description of All the Astrophysical Jets
}}</ref> Jets may also be influenced by a [[general relativity]] effect known as [[frame-dragging]].<ref>{{Cite journal|last=Miller-Jones|first=James|date=April 2019|title=A rapidly changing jet orientation in the stellar-mass black-hole system V404 Cygni|journal=Nature|volume=569|issue=7756|pages=374–377|doi=10.1038/s41586-019-1152-0|pmid=31036949|arxiv=1906.05400|bibcode=2019Natur.569..374M|s2cid=139106116|url=https://eprints.soton.ac.uk/431852/1/A_rapidly_changing_jet_orientation_in_the_stellar_mass_black_hole_system_V404_Cygni.pdf}}</ref>
Most of the largest and most active jets are created by [[supermassive black hole]]s (SMBH) in the centre of [[Active galactic nucleus|active galaxies]] such as [[quasar]]s and radio galaxies or within galaxy clusters.<ref>{{cite journal|year=2014|title=A review of Astrophysical Jets|journal=Acta Polytechnica CTU Proceedings|volume=1|issue=1|pages=259–264|bibcode=2014mbhe.conf..259B|doi=10.14311/APP.2014.01.0259|last1=Beall|first1=J. H|doi-access=free}}</ref> Such jets can exceed millions of [[parsec]]s in length.<ref name="Kundt" /> Other astronomical objects that produce, or are caused by, jets include [[cataclysmic variable star]]s, [[X-ray binary|X-ray binaries]] and [[gamma-ray burst]]s (GRB). Jets on a much smaller scale (~parsecs) may be found in star forming regions, including [[T Tauri star]]s and [[Herbig–Haro object]]s; these objects are partially formed by the interaction of jets with the [[interstellar medium]]. [[Bipolar outflow]]s may also be associated with [[protostar]]s,<ref>{{cite web
}}</ref> or with evolved [[post-AGB]] stars, [[planetary nebula]]e and [[bipolar nebula]]e.
==Relativistic jets==
==Relativistic jets==
{{anchor|Relativistic jet}}
[[File:M87 jet.jpg|thumb|left|[[Elliptical galaxy M87]] emitting a relativistic jet, as seen by the [[Hubble Space Telescope]]]]
[[File:M87 jet.jpg|thumb|left|[[Elliptical galaxy M87]] 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 galactic nucleus|active galaxies]], [[radio galaxy|radio galaxies]] or [[quasar]]s, and also by galactic [[stellar black hole]]s, [[neutron star]]s or [[pulsar]]s. Beam lengths may extend between several thousand,<ref>
{{Cite web
|last=Biretta |first=J.
|date=6 Jan 1999
|title=Hubble Detects Faster-Than-Light Motion in Galaxy M87
}}</ref> or millions of parsecs.<ref name="Kundt" /> Jet velocities when approaching the speed of light show significant effects of the [[Special relativity|special theory of relativity]]; for example, [[relativistic beaming]] that changes the apparent beam brightness.<ref>
{{cite journal
|last1=Semenov |first1=V.
|last2=Dyadechkin |first2=S.
|last3=Punsly |first3=B.
|year=2004
|title=Simulations of Jets Driven by Black Hole Rotation
|journal=[[Science (journal)|Science]]
|volume=305 |issue=5686 |pages=978–980
|arxiv=astro-ph/0408371
|bibcode=2004Sci...305..978S
|doi=10.1126/science.1100638
|pmid=15310894
|s2cid=1590734
|url=https://cds.cern.ch/record/789685
}}</ref>
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 SMBH systems are often called [[microquasar]]s and show a large range of velocities. [[SS 433]] jet, for example, has a mean velocity of 0.26[[Speed of light|c]].<ref>{{cite journal |last1=Blundell |first1=Katherine |title=Jet Velocity in SS 433: Its Anticorrelation with Precession-Cone Angle and Dependence on Orbital Phase |journal=The Astrophysical Journal |date=December 2008 |volume=622 |issue=2 |page=129 |doi=10.1086/429663 |arxiv=astro-ph/0410457 |url=https://www.researchgate.net/publication/230936232 |access-date=15 January 2021|doi-access=free }}</ref> Relativistic jet formation may also explain observed gamma-ray bursts, which have the most relativistic jets known, being [[Ultrarelativistic limit|ultrarelativistic]].<ref>{{Cite journal |last1=Dereli-Bégué |first1=Hüsne |last2=Pe’er |first2=Asaf |last3=Ryde |first3=Felix |last4=Oates |first4=Samantha R. |last5=Zhang |first5=Bing |last6=Dainotti |first6=Maria G. |date=2022-09-24 |title=A wind environment and Lorentz factors of tens explain gamma-ray bursts X-ray plateau |journal=Nature Communications |language=en |volume=13 |issue=1 |pages=5611 |doi=10.1038/s41467-022-32881-1 |pmid=36153328 |pmc=9509382 |arxiv=2207.11066 |bibcode=2022NatCo..13.5611D |issn=2041-1723}}</ref>
Mechanisms behind the composition of jets remain uncertain,<ref>
{{Cite journal
|last1=Georganopoulos |first1=M.
|last2=Kazanas |first2=D.
|last3=Perlman |first3=E.
|last4=Stecker |first4=F. W.
|year=2005
|title=Bulk Comptonization of the Cosmic Microwave Background by Extragalactic Jets as a Probe of Their Matter Content
|journal=[[The Astrophysical Journal]]
|volume=625 |issue=2 |pages=656–666
|arxiv=astro-ph/0502201
|bibcode=2005ApJ...625..656G
|doi=10.1086/429558
|s2cid=39743397
}}</ref> though some studies favour models where jets are composed of an electrically neutral mixture of [[Atomic nucleus|nuclei]], [[electron]]s, and [[positron]]s, while others are consistent with jets composed of positron–electron plasma.<ref>
{{cite journal
|last1=Hirotani |first1=K.
|last2=Iguchi |first2=S.
|last3=Kimura |first3=M.
|last4=Wajima |first4=K.
|year=2000
|title=Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C 345
|journal=[[The Astrophysical Journal]]
|volume=545 |issue=1 |pages=100–106
|bibcode=2000ApJ...545..100H
|doi=10.1086/317769
|arxiv = astro-ph/0005394 |s2cid=17274015
}}</ref><ref name="brandeis.edu">[http://pc.astro.brandeis.edu/pdfs/elec-pos.pdf Electron–positron Jets Associated with Quasar 3C 279]</ref><ref name="auto">{{cite web
|last1=Naeye |first1=R.
|last2=Gutro |first2=R.
|date=2008-01-09
|title=Vast Cloud of Antimatter Traced to Binary Stars
}}</ref> 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 hole]]s. 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]].<ref>
{{Cite journal
|last1=Blandford |first1=R. D.
|last2=Znajek |first2=R. L.
|year=1977
|title=Electromagnetic extraction of energy from Kerr black holes
|journal=[[Monthly Notices of the Royal Astronomical Society]]
|volume=179 |issue=3 |pages=433
|bibcode=1977MNRAS.179..433B
|doi=10.1093/mnras/179.3.433
|doi-access=free
|arxiv=astro-ph/0506302}}</ref> 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 process|Penrose mechanism]].<ref>
{{cite journal
|last1=Penrose |first1=R.
|year=1969
|title=Gravitational Collapse: The Role of General Relativity
|journal=[[Rivista del Nuovo Cimento]]
|volume=1 |pages=252–276
|bibcode=1969NCimR...1..252P
}} Reprinted in: {{cite journal
|last1=Penrose |first1=R.
|year=2002
|title="Golden Oldie": Gravitational Collapse: The Role of General Relativity
|journal=[[General Relativity and Gravitation]]
|volume=34 |issue=7 |pages=1141–1165
|bibcode=2002GReGr..34.1141P
|doi=10.1023/A:1016578408204
|s2cid=117459073
}}</ref> 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,<ref>
{{Cite journal
|last=Williams |first=R. K.|author-link=Reva Williams
|year=1995
|title=Extracting X-rays, Ύ-rays, and relativistic e<sup>−</sup>e<sup>+</sup> pairs from supermassive Kerr black holes using the Penrose mechanism
|journal=[[Physical Review]]
|volume=51 |issue=10 |pages=5387–5427
|bibcode=1995PhRvD..51.5387W
|doi=10.1103/PhysRevD.51.5387
|pmid=10018300
}}</ref> and subsequently shown to be a possible mechanism for jet formation.<ref>
{{Cite journal
|last1=Williams |first1=R. K.
|year=2004
|title=Collimated Escaping Vortical Polar e−e+Jets Intrinsically Produced by Rotating Black Holes and Penrose Processes
|journal=[[The Astrophysical Journal]]
|volume=611 |issue=2 |pages=952–963
|arxiv=astro-ph/0404135
|bibcode=2004ApJ...611..952W
|doi=10.1086/422304
|s2cid=1350543
}}</ref> This effect includes using general relativistic [[gravitomagnetism]].
==Relativistic jets from neutron stars==
==Relativistic jets from neutron stars==
[[File:Lighthouse nebula.jpg|thumb|The pulsar IGR J11014-6103 with supernova remnant origin, nebula and jet]]
[[File:Lighthouse nebula.jpg|thumb|The pulsar IGR J11014-6103 with supernova remnant origin, nebula and jet]]
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 (0.8''c''). X-ray observations have been obtained, but there is no detected radio signature nor accretion disk.<ref>
}} Long helical jet of Lighthouse nebula page 7</ref><ref>
{{Cite journal
|last1=Halpern |first1=J. P.
|display-authors=etal
|year=2014
|title=Discovery of X-ray Pulsations from the INTEGRAL Source IGR J11014-6103
|journal=[[The Astrophysical Journal]]
|volume=795 |issue=2 |pages=L27
|arxiv=1410.2332
|bibcode=2014ApJ...795L..27H
|doi=10.1088/2041-8205/795/2/L27
|s2cid=118637856
}}</ref> 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.
{{clear}}
==Other images==
==Other images==
{{clear}}
{{clear}}
Zeile 282:
Zeile 84:
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
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
</gallery>
</gallery>
*
==See also==
*
* [[Disk wind]] slower wide-angle outflow, often occurring together with a jet
* [[Accretion disk]]
* [[Bipolar outflow]]
* [[Blandford–Znajek process]]
* [[Herbig–Haro object]]
* [[Penrose process]]
* [[CGCG 049-033]], elliptical galaxy located 600 million light-years from Earth, known for having the longest galactic jet discovered
* [[Gamma-ray burst]]
* [[Solar jet]]
==References==
{{reflist}}
==External links==
* [http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/990923a.html NASA – Ask an Astrophysicist: Black Hole Bipolar Jets]
* [http://www.space.com/scienceastronomy/blackhole_jets_040817.html SPACE.com – Twisted Physics: How Black Holes Spout Off]
Jets entstehen, wenn ein ObjektGas aus einer rotierenden Scheibe ansammelt (akkretiert). Nur ein Teil des Scheibengases erreicht das Objekt, der andere Teil strömt senkrecht zur Rotationsebene vom Objekt weg. Man spricht von bipolaren Jets, wenn sie zu beiden Seiten der Akkretionsscheibe austreten. Die Kollimation kommt entweder durch den Innenrand der Akkretionsscheibe geometrisch zustande oder durch magnetische Felder.[1]
Für die Entstehung von Jets sind magnetohydrodynamische Prozesse bedeutend, wobei die Details noch nicht vollständig verstanden sind. Jets werden immer im Zusammenhang mit Akkretion beobachtet, dem Einfall von Materie aus der zirkumstellaren Umgebung oder von einem Begleitstern auf einen kompakten Stern. Dabei wird der Drehimpuls aus einer Akkretionsscheibe mit einem hochkollimierten magnetischen Ausfluss effektiv abgeführt. Nach heutiger Vorstellung wird die Energie und der Drehimpuls aus der Scheibe durch ein magnetisches Drehmoment extrahiert, welches durch ein aufgewickeltes magnetisches Feld in der Akkretionsscheibe entsteht. Wenn der Inklinationswinkel klein genug ist, können magnetische Kräfte die Materie entlang der Feldlinien beschleunigen. Jenseits des Alfvénpunktes wird die Materie auch durch die Lorentzkraft beschleunigt. Die Kollimation des Jets wird durch magnetische Kräfte aufgrund der toroidalen Struktur des Magnetfelds bzw. durch einen höheren Gasdruck in der Korona der Akkretionsscheibe erreicht.[2][3]
2024 wurde das bisher längste Jetpaar Porphyrion entdeckt, das von einem supermassereichen Schwarzen Loch in der Radiogalaxie J152932.16+601534.4 ausstrahlt. Die Radiostrahlung des 24 Mio. Lichtjahre langen Jetpaares zielt auf die nahegelegene Galaxie ab.[4]
Bei Jets, die sich dem Beobachter direkt oder schräg nähern, kann es scheinbar zu Überlichtgeschwindigkeit kommen. Wenn der Jet in einem Winkel von 45° zum Beobachter ausgestoßen wird, tritt dies bereits ab einer Jetgeschwindigkeit von (71 % der Lichtgeschwindigkeit) auf. Dies ist so zu erklären, dass das Licht des sich nähernden Jets eine immer kürzere Zeit benötigt, um zum Beobachter zu gelangen. Dadurch sieht es für den Beobachter so aus, als bewege sich der Jet in transversaler Richtung in kürzerer Zeit als in Wirklichkeit. (siehe: Überlichtgeschwindigkeit → Kosmische Jets)
Jets, die sich vom Beobachter entfernen, erscheinen entsprechend langsamer, da das Licht in diesem Fall einen immer längeren statt kürzeren Weg zurücklegen muss. Im Grenzfall rein transversaler Richtung kann ihre reale Geschwindigkeit beobachtet werden.[7]
Strahlung
Im Falle aktiver Galaxien sind die Wolken vor allem im Radiobereich gut messbar. Zehn aktive Galaxienkerne (hauptsächlich Blazare) wurden von den Teleskopen EGRET und COMPTEL des Compton Gamma Ray Observatory im hochenergetischen MeV- bis GeV-Bereich gemessen. Als Erklärung der Quelle dieser außergewöhnlich energiereichen Strahlung werden verschiedene Modelle diskutiert, u. a. die „niederenergetische“ Synchrotronstrahlung des Jets selbst, die durch den inversen Compton-Effekt durch Stoßprozesse mit hochenergetischen Jetelektronen in dieses Energieregime gestreut wird, oder aber Photonen, die von den Wolken in den Jet gestreut werden und dort ebenfalls eine Invers-Compton-Streuung zu höheren Energien erleiden.
Jets sind Quellen einer nicht isotropen Energieabstrahlung, da auf relativistische Geschwindigkeit beschleunigte Jets die meiste Energie in ihre Ausbreitungsrichtung abstrahlen. Nach aktuellen Hypothesen sind sowohl die langen Gamma Ray Bursts[8] als auch die Ultraleuchtkräftigen Röntgenquellen[9] keine isotropen Strahler mit Energien von bis 1052erg (1045J), sondern emittieren ihre nachgewiesene elektromagnetische Strahlung entlang einer Jetachse mit einer Ausdehnung von nur wenigen Grad.
Weblinks
Russell Blake: Jet. In: spektrum.de. Abgerufen am 24. April 2022.
Jets in Galaxien. In: mpifr-bonn.mpg.de. Abgerufen am 24. April 2022.
↑A. Unsöld, B. Baschek: Der neue Kosmos. Springer Verlag, Berlin 2006, ISBN 978-3-540-42177-1.
↑Somayeh Sheikhnezami et al.: Bipolar jets launched from magnetically diffusive accretion disks. I. Ejection efficiency vs field strength and diffusivity. In: Astrophysics. Solar and Stellar Astrophysics. 2012, arxiv:1207.6086v1.
↑Christian Fendt, Somayeh Sheikhnezami: Bipolar jets launched from accretion disks. II. Formation of symmetric and asymmetric jets and counter jets. In: Astrophysics. Solar and Stellar Astrophysics. 2013, arxiv:1305.1263v1.
↑L. Hartmann: Accretion Processes in Star Formation (Cambridge Astrophysics). Cambridge University Press, Cambridge 2008, ISBN 978-0-521-53199-3.
↑S. N. Shore, M. Livio, E. P. J. van den Heuvel, Astrid Orr, H. Nussbaumer: Interacting Binaries: Saas-Fee Advanced Course 22. Lecture Notes 1992. Swiss Society for Astrophysics and Astronomy (Saas-Fee Advanced Courses). Springer Verlag, Berlin 1993, ISBN 978-3-540-57014-1.
↑P. Schneider: Einführung in die Extragalaktische Astronomie und Kosmologie. Springer Verlag, Berlin 2007, ISBN 978-3-540-25832-2.
↑Jens Hjorth: The supernova/gamma-ray burst/jet connection. In: Astrophysics. Solar and Stellar Astrophysics. 2013, arxiv:1304.7736v1.
↑P. Esposito, S. E. Motta, F. Pintore, L. Zampieri and L. Tomasella: Swift observations of the ultraluminous X-ray source XMMUJ004243.6+412519 in M31. In: Astrophysics. Solar and Stellar Astrophysics. 2012, arxiv:1210.5099.
Supernova remnant Cassiopeia A
Illustration of the dynamics of a proplyd, including a jet
Centaurus A in x-rays showing the relativistic jet
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.)
Galaxy NGC 3862, an extragalactic jet of material moving at nearly the speed of light can be seen at the three o'clock position.
Some of the jets in HH 24-26, which contains the highest concentration of jets known anywhere in the sky
.jpg)