The astropause (heliopause for the Sun) is the tangential discontinuity separating the stellar wind from the interstellar plasma. The global shape of the heliopause is a matter of debates. Two types of the shape are under discussion: comet-like and tube-like. In the second type the two-jets oriented toward the stellar rotation axis are formed by the action of azimuthal component of the stellar magnetic field. We explore a simplified global astrosphere in which: (1) the surrounding and moving with respect to the star circumstellar medium is fully ionized, (2) the interstellar magnetic field is neglected, (3) the radial component of the stellar magnetic field is neglected as compared with the azimuthal component, (4) the stellar wind outflow is spherically symmetric and supersonic. We present the results of numerical 3D MHD modelling and explore how the global structure depends on the gas-dynamic Mach number of the interstellar flow, $M_\infty$, and the Alfvenic Mach number in the stellar wind. It is shown that the astropause has a tube-like shape for small values of $M_\infty$. The wings of the tube are distorted toward the tail as larger as larger the Mach number is. The new (to our knowledge) result is the reverse interstellar flow in the vicinity of the astropause in the tail. The larger the interstellar Mach number is the narrower the reverse flow is. At some values of the Mach number the stellar wind overcomes the reverse interstellar flow and moves out in downwind. In this regime the astropause changes its topology from tube-like to sheet-like.
Magneto-hydrodynamic (MHD) shocks are violent events that inject large amounts of energy in the interstellar medium (ISM) dramatically modifying its physical properties and chemical composition. Indirect evidence for the presence of such shocks has been reported from the especial chemistry detected toward a variety of astrophysical shocked environments. However, the internal physical structure of these shocks remains unresolved since their expected spatial scales are too small to be measured with current instrumentation. Here we report the first detection of a fully spatially resolved, MHD sho…
We present a new 3d self-consistent two-component (plasma and neutral hydrogen) model of the solar wind interaction with the local interstellar medium (LISM). This model (K-MHD) combines the MHD treatment of the solar wind and the ionized LISM component, with a kinetic model of neutral interstellar hydrogen (LISH). The local interstellar magnetic field (BLISM) intensity and orientation are chosen based on an early analysis of the heliosheath flows (Opher et al. 2009). The properties of the plasma and neutrals obtained using the (K-MHD) model are compared to previous multi-fluid (Opher et al. 2…
This paper provides a detailed description of the latest version of our model of the solar wind (SW) interaction with the local interstellar medium (LISM). This model has already been applied to the analysis of Lyman-alpha absorption spectra toward nearby stars and for analyses of Solar and Heliospheric Observatory/SWAN data. Katushkina et al. (this issue) used the model results to analyze IBEX-Lo data. At the same time, the details of this model have not yet been published. This is a three-dimensional (3D) kinetic-magnetohydrodynamical (MHD) model that takes into account SW and interstellar p…
Context. While the shapes of many observed bow shocks can be reproduced by simple astrosphere models, more elaborate approaches have recently been used to explain differing observable structures. Aims. By placing perturbations of an otherwise homogeneous interstellar medium in front of the astrospheric bow shock of the runaway blue supergiant $λ$ Cephei, the observable structure of the model astrosphere is significantly altered, providing insight into the origin of perturbed bow shock images. Methods. Three-dimensional single-fluid magnetohydrodynamic (MHD) models of stationary astrospheres we…
This study is motivated by recent observations on the ubiquitous interstellar density filaments and guided by the modern theory of magnetohydrodynamic (MHD) turbulence. The interstellar turbulence shapes the observed density structure. The perpendicular turbulent mixing, as the fundamental dynamics of MHD turbulence, naturally entails parallel filaments presented in both the diffuse medium and molecular clouds (MCs). The minimum width is determined by the perpendicular neutral-ion decoupling scale in partially ionized media. Differently, dense perpendicular filaments arise in highly supersonic…
A stellar wind passing through the reverse shock is deflected into the astrospheric tail and leaves the stellar system either as a sub-Alfvenic or as a super-Alfvenic tail flow. An example is our own heliosphere and its heliotail. We present an analytical method of calculating stationary, incompressible, and field-aligned plasma flows in the astrotail of a star. We present a recipe for constructing an astrosphere with the help of only a few parameters, like the inner Alfven Mach number and the outer Alfven Mach number, the magnetic field strength within and outside the stellar wind cavity, and…
This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability in the atomic gas and of moderately-to-strongly supersonic…
Neutral hydrogen has been shown to greatly impact the plasma flow in the heliopshere and the location of the heliospheric boundaries. We present the results of the Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic-MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge-exchange mean free path is on order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The SHIELD model couples the MHD solution for a single plasma fluid to the kinetic solution from for neut…
We present a comprehensive study of MHD waves and instabilities in a weakly ionised system, e.g., an interstellar molecular cloud. We determine all the critical wavelengths of perturbations across which the sustainable wave modes can change radically (and so can their decay rates), and various instabilities are present or absent. These critical wavelengths are essential for understanding the effects of MHD waves (or turbulence) on the structure and evolution of molecular clouds. Depending on the angle of propagation relative to the magnetic field and the physical parameters of a cloud, there a…
The understanding of inertial-scale dynamics in the heliosheath is not yet thorough. Magnetic field fluctuations across the inner heliosheath (IHS) and the local interstellar medium (LISM) are here considered to provide accurate and highly resolved statistics over different plasma conditions between 88 and 136 au. By using the unique in situ 48 s measurements from the Voyager Interstellar Mission, we investigate different fluctuation regimes at the magnetohydrodynamic (MHD) scales, down to the MHD-to-kinetic transition. We focus on a range of scales exceeding five frequency decades (5 x 10-8 <…
Protostellar disks in their natural habitat -- the formation of protostars and their accretion disks in the turbulent and magnetized interstellar medium
The geometrical shapes and the physical properties of stellar wind -- interstellar medium interaction regions form an important stage for studying stellar winds and their embedded magnetic fields as well as cosmic ray modulation. Our goal is to provide a proper representation and classification of counter-flow configurations and counter-flow interfaces in the frame of fluid theory. In addition we calculate flows and large-scale electromagnetic fields based on which the large-scale dynamics and its role as possible background for particle acceleration, e.g. in the form of anomalous cosmic rays,…
We examine the evolution and emission of the supernova remnant (SNR) CTB109 using three-dimensional magnetohydrodynamics simulations. The SNR evolves in a medium divided by a plane interface into two media with different densities and pressure equilibrium. Our results reveal that a remnant with the characteristics of CTB109 is formed provided the supernova (SN) explosion takes place in the less dense medium and also if the interstellar magnetic field (ISMF) is almost uniform. Finally, we conclude that the quasiparallel mechanism can explain the brightness synchrotron emission and the position …
We examine MHD simulations of the propagation of a strong shock wave through the interstellar two-phase medium composed of small-scale cloudlets and diffuse warm neutral medium in two-dimensional geometry. The pre-shock two-phase medium is provided as a natural consequence of the thermal instability that is expected to be ubiquitous in the interstellar medium. We show that the shock-compressed shell becomes turbulent owing to the preshock density inhomogeneity and magnetic field amplification takes place in the shell. The maximum field strength is determined by the condition that plasma beta ~…
The transport of energetic particles such as Cosmic Rays is governed by the properties of the plasma being traversed. While these properties are rather poorly known for galactic and interstellar plasmas due to the lack of in situ measurements, the heliospheric plasma environment has been probed by spacecraft for decades and provides a unique opportunity for testing transport theories. Of particular interest for the 3D heliospheric transport of energetic particles are structures such as corotating interaction regions (CIRs), which, due to strongly enhanced magnetic field strengths, turbulence, …
Three dimensional magnetohydrodynamical simulations were carried out in order to perform a new polarization study of the radio emission of the supernova remnant SN 1006. These simulations consider that the remnant expands into a turbulent interstellar medium (including both magnetic field and density perturbations). Based on the referenced-polar angle technique, a statistical study was done on observational and numerical magnetic field position-angle distributions. Our results show that a turbulent medium with an adiabatic index of 1.3 can reproduce the polarization properties of the SN 1006 r…
Magnetic field lines in interstellar media have a rich morphology, which could be characterized by geometrical parameters such as curvature and torsion. In this paper, we explore the statistical properties of magnetic field line curvature $κ$ in compressible magnetized turbulence. We see that both the mean and standard deviation of magnetic field line curvature obey power-law relations to the magnetization. Moreover, the power-law tail of the curvature probability distribution function is also proportional to the Alfvenic Mach number. We also explore whether the curvature method could be used …
Magnetohydrodynamic (MHD) turbulence in the majority of natural systems, including the interstellar medium, the solar corona, and the solar wind, has Reynolds numbers far exceeding the Reynolds numbers achievable in numerical experiments. Much attention is therefore drawn to the universal scaling properties of small-scale fluctuations, which can be reliably measured in the simulations and then extrapolated to astrophysical scales. However, in contrast with hydrodynamic turbulence, where the universal structure of the inertial and dissipation intervals is described by the Kolmogorov self-simila…
During Parker Solar Probe's first orbit, the solar wind plasma has been observed in situ closer than ever before, the perihelion on November 6th 2018 revealing a flow that is constantly permeated by large amplitude Alfvénic fluctuations. These include radial magnetic field reversals, or switchbacks, that seem to be a persistent feature of the young solar wind. The measurements also reveal a very strong, unexpected, azimuthal velocity component. In this work, we numerically model the solar corona during this first encounter, solving the MHD equations and accounting for Alfvén wave transport and…
Interstellar Pickup ions (PUIs) play a significant part in mediating the solar wind (SW) interaction with the interstellar medium. In this paper, we examine the details of spatial variation of the PUI velocity distribution function (VDF) in the SW by solving the PUI transport equation. We assume the PUI distribution is isotropic resulting from strong pitch-angle scattering by wave-particle interaction. A three-dimensional model combining the MHD treatment of the background SW and neutrals with a kinetic treatment of PUIs throughout the heliosphere and the surrounding local interstellar medium …
The solar wind and the interstellar medium are permeated by large-scale magnetic fields that render magnetohydrodynamic (MHD) turbulence anisotropic. In the weak-turbulence limit in which three-wave interactions dominate, analytical and high-resolution numerical results based on random scattering of shear-Alfvén waves propagating parallel to a large-scale magnetic field, as well as direct simulations demonstrate rigorously an anisotropic energy spectrum that scales as $k^{-2}_\perp$, instead of the famous Iroshnikov-Kraichnan (IK) spectrum of $k^{-3/2}$ for the isotropic case. Even in the abse…
Classical, large scale 3D MHD simulations of interacting pulsar wind nebulae
Institute of Space Sciences (ICE, CSIC)（空间科学研究所）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Institució Catalana de Recerca i Estudis Avançats (ICREA)（加泰罗尼亚高级研究制度）
A variety of studies of magnetised plasma turbulence invoke theories for the advection of a passive scalar by turbulent fluctuations. Examples include modelling the electron density fluctuations in the interstellar medium, understanding the chemical composition of galaxy clusters and the intergalactic medium, and testing the prevailing phenomenological theories of magnetohydrodynamic turbulence. While passive scalar turbulence has been extensively studied in the hydrodynamic case, its counterpart in MHD turbulence is significantly less well understood. Herein we conduct a series of high-resolu…
We investigate how a weak coronal mass ejection (CME) launched on 2016 October 8 without obvious signatures in the low corona produced a relatively intense geomagnetic storm. Remote sensing observations from SDO, STEREO and SOHO and in situ measurements from WIND are employed to track the CME from the Sun to the Earth. Using a graduated cylindrical shell (GCS) model, we estimate the propagation direction and the morphology of the CME near the Sun. CME kinematics are determined from the wide-angle imaging observations of STEREO A and are used to predict the CME arrival time and speed at the Ear…
The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun's travel through the interstellar medium (ISM) extending for 1000's of AUs (AU: astronomical unit). Here we show, based on magnetohydrodynamic (MHD) simulations, that the tension (hoop) force of the twisted magnetic field of the sun confines the solar wind plasma beyond the termination shock and drives jets to the North and South very much like astrophysical jets. These jets are deflected into the tail region by the motion of the Sun through the ISM similar to bent galactic jets mo…
The effects of turbulence in the very local interstellar medium (VLISM) have been proposed by Giacalone & Jokipii (2015) to be important in determining the structure of the Interstellar Boundary Explorer (IBEX) ribbon via particle trapping by magnetic mirroring. We further explore this effect by simulating the motion of charged particles in a turbulent magnetic field superposed on a large-scale mean field, which we have considered to be either spatially-uniform or a mean field derived from a 3D MHD simulation. We find that the ribbon is not double-peaked, in contrast to Giacalone & Jokipii (20…
Energetic neutral atom (ENA) models typically require post-processing routines to convert the distributions of plasma and H atoms into ENA maps. Here we investigate how two different kinetic-MHD models of the heliosphere (the BU and Moscow models) manifest in modeled ENA maps using the same prescription and how they compare with Interstellar Boundary Explorer (IBEX) observations. Both MHD models treat the solar wind as a single-ion plasma for protons, which include thermal solar wind ions, pick-up ions (PUIs), and electrons. Our ENA prescription partitions the plasma into three distinct ion po…
Interplay between Escaping Cosmic Rays and Interstellar Medium: Driving of Galactic Winds and Shaping the Local Proton Spectrum
Institute for Cosmic Ray Research, The University of Tokyo（东京大学宇宙射线研究所）；Department of Physics, Graduate School of Science, Nagoya University（名古屋大学理学研究科物理学系）
