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The interstellar medium (ISM) is constantly evolving due to unremitting injection of energy in various forms. Energetic radiation transfers energy to the ISM: from the UV photons, emitted by the massive stars, to X- and $\gamma$-ray ones.…
We study the nonlinear evolution of the magnetic buoyancy instability in rotating and non-rotating gas layers using numerical solutions of non-ideal, isothermal MHD equations. The unstable magnetic field is either imposed through the…
In the Milky Way, cosmic rays (CRs) are dynamically important in the interstellar medium, contribute to hydrostatic balance, and may help regulate star formation. However, we know far less about the importance of CRs in galaxies whose gas…
Late in their evolution, massive stars may undergo periods of violent instability and mass loss, but the mechanism responsible for these episodes has not been identified. We study one potential contributor: the development of local…
Recent cosmic-ray measurements by the ATIC, CREAM and PAMELA experiments have found an apparent hardening of the energy spectrum at TeV energies. Although the origin of the hardening is not clearly understood, possible explanations include…
Using a hydrodynamic adaptive mesh refinement code, we simulate the growth and evolution of a galaxy, which could potentially host a supermassive black hole, within a cosmological volume. Reaching a dynamical range in excess of 10 million,…
We numerically study the origin of the multi-armed spiral structure observed in the circumnuclear gaseous mini-disks of nearby galaxies. We show that the presence of dust in such disks and its interaction with the gravitationally stable…
The recently emerging conviction that thick disks are prevalent in disk galaxies, and their seemingly ubiquitous old ages, means that the formation of the thick disk, perhaps more than any other component, holds the key to unravelling the…
Understanding star formation is problematic as it originates in the large scale dynamics of a galaxy but occurs on the small scale of an individual star forming event. This paper presents the first numerical simulations to resolve the star…
The origin of cosmic rays above the knee in the spectrum is an unsolved problem. We present a wind model in which interstellar gas flows along a non-rotating, expanding flux tube with a changing speed and cross-sectional area. Cosmic rays…
Precise measurements of galactic cosmic rays revealed a significant difference between the rigidity spectral indices of protons and helium ions. This finding is a notable contrast to the commonly accepted theoretical prediction that…
The interstellar medium (ISM) is a key ingredient of galaxies and their evolution, consisting of multiphase, turbulent dust and gas. Some of the star-forming regions in our Galaxy originate from cloud-cloud and wind-cloud collisions, which…
The main observational evidence for turbulence in the interstellar medium (ISM) and molecular clouds is the power-law energy spectrum for velocity fluctuations, E(k) \propto k^{\alpha}. The Kolmogorov scaling exponent, \alpha=-5/3, is…
We present a new analytic tool for the study of cosmic structure formation, a double distribution of the number density of dark matter halos with respect to both halo mass and local over- (or under-) density. The double distribution…
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization…
Relativistic astrophysical phenomena such as gamma-ray bursts (GRBs) and active galactic nuclei often require long-lived strong magnetic field. Here, we report on three-dimensional special-relativistic magnetohydrodynamic (MHD) simulations…
We analyze the main features of radiation-mediated shocks at arbitrary shock velocities, both non-relativistic and relativistic. We describe two mechanisms, which may lead to formation of a sharp viscous subshock within otherwise smooth…
Studies of energetic particle acceleration at collisionless shocks by the diffusive shock acceleration process indicate that completely smooth cosmic ray dominated shock structures are possible. The existence of these is discussed and…
(substantial changes to section 3.2, otherwise minor) We present an analysis of the hydrodynamic stability of a cold slab bounded by two accretion shocks. Previous numerical work has shown that when the Mach number of the shock is large the…
We investigate the coupling between rock-size solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. In this study, we use three-dimensional radiative hydrodynamics simulations…