Beam of ionized matter flowing along the axis of a rotating astronomical object
An astrophysical jet is an
astronomical phenomenon where outflows of
ionised matter are emitted as extended beams along the
axis of rotation.[1] When this greatly accelerated matter in the beam approaches the
speed of light, astrophysical jets become relativistic jets as they show effects from
special relativity.
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 disks, whose active processes are commonly connected with compact central objects such as
black holes,
neutron stars or
pulsars. One explanation is that tangled
magnetic fields are organised to aim two diametrically opposing beams away from the central source by angles only several degrees wide (c. > 1%).[2] Jets may also be influenced by a
general relativity effect known as
frame-dragging.[3]
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,[6] hundreds of thousands[7] or millions of parsecs.[2] Jet velocities when approaching the speed of light show significant effects of the
special theory of relativity; for example,
relativistic beaming that changes the apparent beam brightness.[8]
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
microquasars and show a large range of velocities.
SS 433 jet, for example, has a mean velocity of 0.26
c.[9] Relativistic jet formation may also explain observed
gamma-ray bursts, which have the most relativistic jets known, being
ultrarelativistic.[10]
Mechanisms behind the composition of jets remain uncertain,[11] 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.[12][13][14] 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.[15] 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.[16] 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,[17] and subsequently shown to be a possible mechanism for jet formation.[18] 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 nor accretion disk.[19][20] Initially, this pulsar was presumed to be rapidly spinning, but later measurements indicate the spin rate is only 15.9 Hz.[21][22] 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
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.)
Hubble Legacy Archive Near-
UV image of the relativistic jet in
3C 66B
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