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Register a new userThe collimated propagation causes of astrophysical and laboratory jets
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The use of Z-pinch facilities makes it possible to carry out well-controlled and diagnosable laboratory experiments to study laboratory jets with scaling parameters close to those of the jets from young stars. This makes it possible to observe processes that are inaccessible to astronomical observations. Such experiments are carried out at the PF-3 facility (plasma focus, Kurchatov Institute), in which the emitted plasma emission propagates along the drift chamber through the environment at a distance of one meter. The paper presents the results of experiments with helium, in which a successive release of two ejections was observed. An analysis of these results suggests that after the passage of the first supersonic ejection, a region with a low concentration is formed behind it, the so-called vacuum trace, due to which the subsequent ejection practically does not experience environmental resistance and propagates being collimated. The numerical modeling of the propagation of two ejections presented in the paper confirms this point of view. Using scaling laws and appropriate numerical simulations of astrophysical ejections, it is shown that this effect can also be significant for the jets of young stars.
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The results of MHD numerical simulations of the formation and development of magnetized jets are presented. Similarity criteria for comparisons of the results of laboratory laser experiments and numerical simulations of astrophysical jets are discussed. The results of laboratory simulations of jets generated in experiments at the Neodim laser installation are presented.
The paper presents the results of numerical simulation of the propagation of a sequence of plasma knots in laboratory conditions and the astrophysical environment. The physical and geometric parameters of the simulation have been chosen close to the parameters of the PF-3 facility (Kurchatov Institute) and the jet of the star RW Aur. We found that the low-density region formed after the first knot propagation plays an important role for collimation of the subsequent ones. Assuming only the thermal expansion of the subsequent emissions, qualitative estimates of the time taken to fill this area with the surrounding matter and the angle of jet scattering have been made. These estimates are consistent with observations and results of our modeling.
In this chapter, we review some features of particle acceleration in astrophysical jets. We begin by describing four observational results relating to the topic, with particular emphasis on jets in active galactic nuclei and parallels between different sources. We then discuss the ways in which particles can be accelerated to high energies in magnetised plasmas, focusing mainly on shock acceleration, second-order Fermi and magnetic reconnection; in the process, we attempt to shed some light on the basic conditions that must be met by any mechanism for the various observational constraints to be satisfied. We describe the limiting factors for the maximum particle energy and briefly discuss multimessenger signals from neutrinos and ultrahigh energy cosmic rays, before describing the journey of jet plasma from jet launch to cocoon with reference to the different acceleration mechanisms. We conclude with some general comments on the future outlook.
The constraint imposed by magnetic helicity conservation on the alpha effect is considered for both magnetically and flow dominated self-organizing plasmas. Direct numerical simulations are presented for a dominant contribution to the alpha effect, which can be cast in the functional form of a total divergence of an averaged helicity flux, called the helicity-flux-driven alpha ( H$alpha$) effect. Direct numerical simulations of the H$alpha$ effect are prese nted for two examples---the magnetically dominated toroidal plasma unstable to tearing modes, and the flow-dominated accretion disk.
We present six case studies from a broad mass range ($1 - 10^9$ $M_odot$) of astrophysical objects, each of which exhibit signs of jets and emit intense high energy gamma rays ($>10$ GeV). Many of these objects also emit spatially identifiable ultra high energy cosmic rays (UHECRs). In all cases it is found that wakefield acceleration (WFA) explains both the global properties and details. For blazars, we also explain the temporal structure of these signals, which includes neutrinos, and the correlations in their bursts and anti-correlation in flux and index. Blazars ($sim 10^9$ $M_odot$), radio galaxies ($sim 10^8, M_{odot}$), Seyfert galaxies ($sim 10^6 ,M_{odot}$), starburst galaxies ($sim 10^{3}, M_{odot}$), down to microquasars ($1 sim 10$ $M_odot$) interestingly exhibit the same physics since the nature of the accretion and acceleration is independent of the mass, aside from maximum values. It is possible to accelerate electrons to energies much greater than $10$ GeV, and protons beyond $10^{20}$ eV with WFA. We compare observational values with theoretical ones to illustrate they are in good agreement. This mechanism is also accompanied by related emissions, such as high-energy pin-pointed neutrinos, time varying radio, optical, and X-ray emissions, opening an opportunity to characterize these astrophysical objects via multi-messenger approaches.
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