1,514 research outputs found
Jet dynamics. Recollimation shocks and helical patterns
The dynamics and stability of extragalactic jets may be strongly influenced
by small (and probable) differences in pressure between the jet and the ambient
and within the jet itself. The former give rise to expansion and recollimation
of the jet. This occurs in the form of conical shocks, or Mach disks, if the
pressure difference is large enough. Pressure asymmetries within the jet may
trigger the development of helical patterns via coupling to kink current-driven
instability, or to helical Kelvin-Helmholtz instability, depending on the
physical conditions in the jet. I summarize here the evidence collected during
the last years on the presence of recollimation shocks and waves in jets. In
the jet of CTA 102 evidence has been found for (traveling)shock-(standing)shock
interaction in the core-region (0.1 mas from the core), using information from
the light-curve of the source combined with VLBI data. The conclusions derived
have been confirmed by numerical simulations combined with emission
calculations that have allowed to study the spectral evolution of the perturbed
jet. Helical structures can also be identified in radio-jets. The ridge-line of
emission of the jet of S5~0836+710 has been identified as a physical structure
corresponding to a wave developing in the jet flow. I review here the evidence
that has allowed to reach this conclusion, along with an associated caveat.
Current data do not allow to distinguish between magnetic or hydrodynamical
instabilities. I finally discuss the importance of these linear and non-linear
waves for jet evolution.Comment: 11 pages. Proceedings of the conference: The innermost regions of
relativistic jets and their magnetic fields. Corrected typos and added
reference
Jet stability, dynamics and energy transport
Relativistic jets carry energy and particles from compact to very large
scales compared with their initial radius. This is possible due to their
remarkable collimation despite their intrinsic unstable nature. In this
contribution, I review the state-of-the-art of our knowledge on instabilities
growing in those jets and several stabilising mechanisms that may give an
answer to the question of the stability of jets. In particular, during the last
years we have learned that the limit imposed by the speed of light sets a
maximum amplitude to the instabilities, contrary to the case of classical jets.
On top of this stabilising mechanism, the fast growth of unstable modes with
small wavelengths prevents the total disruption and entrainment of jets. I also
review several non-linear processes that can have an effect on the collimation
of extragalactic and microquasar jets. Within those, I remark possible causes
for the decollimation and decelleration of FRI jets, as opposed to the
collimated FRII's. Finally, I give a summary of the main reasons why jets can
propagate through such long distances.Comment: For the proceedings of High Energy Phenomena in Relativistic Outflows
III (HEPRO III, IJMPD, accepted). 12 page
3D simulations of wind-jet interaction in massive X-ray binaries
High-mass microquasars may produce jets that will strongly interact with
surrounding stellar winds on binary system spatial scales. We study the
dynamics of the collision between a mildly relativistic hydrodynamical jet of
supersonic nature and the wind of an OB star. We performed numerical 3D
simulations of jets that cross the stellar wind with the code Ratpenat. The jet
head generates a strong shock in the wind, and strong recollimation shocks
occur due to the initial overpressure of the jet with its environment. These
shocks can accelerate particles up to TeV energies and produce gamma-rays. The
recollimation shock also strengthens jet asymmetric Kelvin-Helmholtz
instabilities produced in the wind/jet contact discontinuity. This can lead to
jet disruption even for jet powers of several times erg s.
High-mass microquasar jets likely suffer a strong recollimation shock that can
be a site of particle acceleration up to very high energies, but also
eventually lead to the disruption of the jet.Comment: Accepted for publication in A&A Letter
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