Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user3D simulations of the early stages of AGN jets: geometry, thermodynamics and backflow
170
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate the interplay between jets from Active Galactic Nuclei (AGNs) and the surrounding InterStellar Medium (ISM) through full 3D, high resolution, Adaptive Mesh Refinement simulations performed with the FLASH code. We follow the jet- ISM system for several Myr in its transition from an early, compact source to an extended one including a large cocoon. During the jet evolution, we identify three major evolutionary stages and we find that, contrary to the prediction of popular theoretical models, none of the simulations shows a self-similar behavior. We also follow the evolution of the energy budget, and find that the fraction of input power deposited into the ISM (the AGN coupling constant) is of order of a few percent during the first few Myr. This is in broad agreement with galaxy formation models employing AGN feedback. However, we find that in these early stages, this energy is deposited only in a small fraction (< 1%) of the total ISM volume. Finally we demonstrate the relevance of backflows arising within the extended cocoon generated by a relativistic AGN jet within the ISM of its host galaxy, previously proposed as a mechanism for self-regulating the gas accretion onto the central object. These backflows tend later to be destabilized by the 3D dynamics, rather than by hydrodynamic (Kelvin- Helmholtz) instabilities. Yet, in the first few hundred thousand years, backflows may create a central accretion region of significant extent, and convey there as much as a few millions of solar masses.
rate research
Read More
The formation mechanism of the W50/SS433 complex has long been a mystery. We propose a new scenario in which the SS433 jets themselves form the W50/SS433 system. We carry out magnetohydrodynamics simulations of two-side jet propagation using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times, and afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology strongly depends on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two-side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.
We present 15 GHz stacked VLBA images of 373 jets associated with active galactic nuclei (AGN) having at least five observing epochs within a 20 yr time interval 1994-2015 from the MOJAVE programme and/or its precursor, the 2 cm VLBA Survey. These data are supplemented by 1.4 GHz single-epoch VLBA observations of 135 MOJAVE AGNs to probe larger scale jet structures. The typical jet geometry is found to be close to conical on scales from hundreds to thousands of parsecs, while a number of galaxies show quasi-parabolic streamlines on smaller scales. A true jet geometry in a considerable fraction of AGNs appears only after stacking epochs over several years. The jets with significant radial accelerated motion undergo more active collimation. We have analysed total intensity jet profiles transverse to the local jet ridgeline and derived both apparent and intrinsic opening angles of the flows, with medians of $21.5deg$ and $1.3deg$, respectively. The Fermi LAT-detected gamma-ray AGNs in our sample have, on average, wider apparent and narrower intrinsic opening angle, and smaller viewing angle than non LAT-detected AGNs. We have established a highly significant correlation between the apparent opening angle and gamma-ray luminosity, driven by Doppler beaming and projection effects.
Relativistic jets naturally occur in astrophysical systems that involve accretion onto compact objects, such as core collapse of massive stars in gamma-ray bursts (GRBs) and accretion onto supermassive black holes in active galactic nuclei (AGN). It is generally accepted that these jets are powered electromagnetically, by the magnetised rotation of a central compact object. However, how they produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven non-axisymmetric instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic simulations of relativistic, Poynting flux dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetised central compact object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time scales and causes the jets to bodily bend sideways. Whereas this mode does not cause jet disruption over the simulated distances, it substantially reduces jet propagation speed. We show, via an analytic model, that the growth of the external kink mode depends on the slope of the ambient medium density profile. In flat density distributions characteristic of galactic cores, an AGN jet may stall, whereas in stellar envelopes the external kink weakens as the jet propagates outward; (ii) a local, internal kink mode that grows over short time scales and causes small-angle magnetic reconnection and conversion of about half of jet electromagnetic energy flux into heat. Based on the robustness and energetics of the internal kink mode, we suggest that this instability is the main dissipation mechanism responsible for powering GRB prompt emission.
In this paper, we investigate the acceleration in relativistic jets of high-energy proton preaccelerated in the magnetosphere of a supermassive black hole. The proton reaches maximum energy when passing the total potential difference of $U$ between the jet axis and its periphery. This voltage is created by a rotating black hole and transmitted along magnetic field lines into the jet. It is shown that the trajectories of proton in the jet are divided into three groups: untrapped, trapped and not accelerated. Untrapped particles are not kept by poloidal and toroidal magnetic fields inside the jet, so they escape out the jet and their energy is equal to the maximum value, $eU$. Trapped protons are moving along the jet with oscillations in the radial direction. Their energy varies around the value of $0.74 eU$. In a strong magnetic field protons preaccelerated in the magnetosphere are pressed to the jet axis and practically are not accelerated in the jet. The work defines acceleration regimes for a range of the most well-known AGN objects with relativistic jets and for the microquasar SS433.
High-mass microquasars consist of a massive star and a compact object, the latter producing jets that will interact with the stellar wind. The evolution of the jets, and ultimately their radiative outcome, could depend strongly on the inhomogeneity of the wind, which calls for a detailed study. The hydrodynamics of the interaction between a jet and a clumpy wind is studied, focusing on the global wind and single clump-jet interplay. We have performed, using the code textit{Ratpenat}, three-dimensional numerical simulations of a clumpy wind interacting with a mildly relativistic jet, and of individual clumps penetrating into a jet. For typical wind and jet velocities, filling factors of about > 0.1 are already enough for the wind to be considered as clumpy. An inhomogeneous wind makes the jet more unstable when crossing the system. Kinetic luminosities of the order 1.e37 erg/s allow the jet to reach the borders of a compact binary with an O star, as in the smooth wind case, although with a substantially higher degree of disruption. When able to enter into the jet, clumps are compressed and heated during a time of about their size divided by the sound speed in the shocked clump. Then, clumps quickly disrupt, mass-loading and slowing down the jet. We conclude that moderate wind clumpiness makes already a strong difference with the homogeneous wind case, enhancing jet disruption, mass-loading, bending, and likely energy dissipation in the form of emission. All this can have observational consequences at high-energies and also in the large scale radio jets.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
