An astrophysical jet is an astronomical phenomenon where outflows of

ionised Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

matter are emitted as an extended beam along the

axis of rotation Rotation around a fixed axis is a special case of rotational motion. The fixed- axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's r ...

. When this greatly accelerated matter in the beam approaches the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...

, astrophysical jets become relativistic jets as they show effects from

special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The law ...

. The formation and powering of astrophysical jets are highly complex phenomena that are associated with many types of high-energy astronomical sources. They likely arise from dynamic interactions within

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other ...

s, whose active processes are commonly connected with compact central objects such as

black hole A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can def ...

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

s or

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

s. One explanation is that tangled

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

s are organised to aim two diametrically opposing beams away from the central source by angles only several degrees wide Jets may also be influenced by a

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

effect known as frame-dragging. Most of the largest and most active jets are created by supermassive black holes (SMBH) in the centre of

active galaxies An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pro ...

such as quasars and radio galaxies or within galaxy clusters. Such jets can exceed millions of parsecs in length. Other astronomical objects that contain jets include

cataclysmic variable star In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since ones with an outburst brightness visible to ...

X-ray binaries X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal star), to the other component, called the ''accretor'', which ...

and gamma-ray bursts (GRB). Jets on a much smaller scale (~parsecs) may be found in star forming regions including T Tauri stars and Herbig–Haro objects; these objects are partially formed by the interaction of jets with the

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

. Bipolar outflows may also be associated with protostars, or with evolved

post-AGB The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) late ...

stars, planetary nebulae and bipolar nebulae.

Relativistic jets

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

, radio galaxies or quasars, and also by galactic

stellar black hole A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a ...

s or

s. Beam lengths may extend between several thousand, hundreds of thousands or millions of parsecs. Jet velocities when approaching the speed of light show significant effects of the

special theory of relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The law ...

; for example,

relativistic beaming Relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of ligh ...

that changes the apparent beam brightness. M87 jet

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

s. These SMBH systems are often called microquasars and show a large range of velocities.

SS 433 SS 433 is one of the most exotic star systems observed. It is located in the Milky Way galaxy, and is an eclipsing X-ray binary system, with the primary being a stellar-mass black hole. The spectrum of the secondary companion star sugg ...

jet, for example, has a mean velocity of 0.26 c. Relativistic jet formation may also explain observed gamma-ray bursts. Mechanisms behind the composition of jets remain uncertain, though some studies favour models where jets are composed of an electrically neutral mixture of nuclei,

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

s, and

positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collide ...

s, while others are consistent with jets composed of positron–electron plasma.Electron–positron Jets Associated with Quasar 3C 279
/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

s. However, the frequency of high-energy astrophysical sources with jets suggest 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 Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy. A stationary field is one that is in a steady state, but the masses cau ...

, which was later theoretically proven 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 Gravitoelectromagnetism, abbreviated GEM, refers to a set of formal analogies between the equations for electromagnetism and relativistic gravitation; specifically: between Maxwell's field equations and an approximation, valid under certain ...

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 The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

, 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. 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 The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~ west of Socorro. The VLA comprises twent ...

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the up ...

(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 3C 66B is an elliptical Fanaroff and Riley class 1 radio galaxy located in the constellation Andromeda. With an estimated redshift of 0.021258, the galaxy is about 300 million light-years away. The orbital motion of 3C 66B showed supposed ...

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

References

External links