We discuss the lifetimes and evolution of clumps cores formed as turbulent density fluctuations in nearly isothermal molecular clouds. In non-magnetic case, are unlikely to reach a hydrostatic state, instead expected either proceed directly collapse, or else ``rebound'' towards mean pressure parent cloud. Rebounding delayed their re-expansion by self-gravity. From simple virial calculation, we find times few free-fall times. magnetic present series driven-turbulence, ideal-MHD numerical...

We study the instantaneous virial balance of CCs in numerical models MCs. The represent a range magnetic field strengths MCs from subcritical to nonmagnetic regimes. identify at different density thresholds and calculate, for each object, terms that enter EVT. A CC is gravitationally bound when gravitational term EVT larger than amount system be virialized, which more stringent condition it large enough make total volume energy negative. also calculate other quantities used indicate state...

Abstract We investigate the time-evolution of mass distribution pre-stellar cores (PSCs) and their transition to initial stellar function (IMF) in central parts a molecular cloud (MC) under assumption that coalescence is important. Our aim explain observed shallow IMF dense clusters such as Arches cluster. The distributions PSCs at various distances from MC centre are those gravitationally unstable resulting gravo-turbulent fragmentation MC. As time evolves, there competition between rates...

(abridged) We develop a model which describes the coevolution of mass function dense cores and IMF in protocluster clump. In model, injected clump evolve under effect gas accretion. Accretion onto follows time-dependent accretion rate that turbulent medium. Once timescales exceed their contraction timescales, they are turned into stars. include feedback by newly formed massive stars through stellar winds. A fraction wind's energy is assumed to counter gravity disperse from as consequence,...

Abstract We study the evolution of scalar and tensor cosmological perturbations in framework Einstein–Cartan theory gravity. The value gravitational slip parameter which is defined as ratio two potentials Newtonian gauge, can be used to determine whether or not gravity modified. calculate cosmology show that it falls within observed range. also discuss cosmic waves another measure modification

ABSTRACT We study the stability of a dust layer in gaseous disk subject to linear axisymmetric perturbations. Instead considering single-size particles, however, population particles is assumed consist two grain species. Dust grains exchange momentum with gas via drag force and their self-gravity also considered. show that presence sizes can increase efficiency growth drag-driven instability protoplanetary disks (PPDs). A second phase small mass, compared first phase, would reduce timescale...

We present numerical hydrodynamic simulations of the formation, evolution, and gravitational collapse isothermal molecular cloud cores in spherical geometry. A compressive wave is set up a constant sub-Jeans density distribution radius r = 1 pc. As travels through simulation grid, shock-bounded shell formed. The inner shock this reaches bounces off center, leaving behind central core with an initially almost uniform distribution, surrounded by envelope consisting material shell, which at...

The structure of molecular clouds (MCs) holds important clues on the physical processes that lead to their formation and subsequent evolution. While it is well established turbulence imprints a self-similar clouds, other processes, such as gravity stellar feedback, can break scale-free nature. self-similarity manifest itself in existence characteristic scales stand out from underlying generated by turbulent motions. We investigate Cygnus-X North Polaris MCs which represent two extremes terms...

We study the dynamical effects of cosmic rays (CRs) on thermal instability in linear regime. CRs and plasma are treated as two different interacting fluids, which can diffuse along magnetic field lines. show that growth rate magnetothermal condensation mode is reduced because existence CRs, this stabilizing effect depends diffusion coefficient ratio CR pressure to gas pressure. Thus, a slower structure formation via predicted when considered.

The possibility that the stellar initial mass function (IMF) arises mostly from cloud structure is investigated with fractal Brownian motion (fBm) clouds have power-law power spectra. An fBm a realistic projected spectrum slope of β= 2.8 found to for clumps exceeding threshold density law α= 2.35, same as in Salpeter IMF. Any hierarchically structured has clump about slope. This result implies turbulent interstellar produce dense substructure observed pre-stellar core built start. Details...

We study thermal instability in a magnetized and partially ionized plasma with charged dust particles. Our linear analysis shows that the growth rate of unstable modes presence particles strongly depends on ratio cooling modified dust-cyclotron frequency. If is less than frequency, then condensation does not modify due to existence But when greater (or comparable to) increases because Also, wavenumber perturbations corresponding maximum shifts smaller values (larger wavelengths) as becomes...

ABSTRACT Observational evidence and theoretical arguments postulate that outflows may play a significant role in the advection-dominated accretion discs (ADAFs). While azimuthal viscosity is main focus of most previous studies this context, recent indicated disc structure can also be affected by radial viscosity. In work, we incorporate these physical ingredients toroidal component magnetic field to explore their roles steady-state ADAFs. We thereby present set similarity solutions where...

The millimetre-wave continuum sources (MCS) in Ophiuchus have mutual collision rates less than their collapse by a factor of 10 to 100, suggesting that most will form stars without further interactions. However, the ratio these would exceeded unity past if they were only 2.5 times larger are now. Such high previous suggests three possible scenarios: (1) MCS contracted from lower densities and acquired present masses through collisional agglomeration, (2) independently elsewhere moved cluster...

A coalescence model using the observed properties of pre‐stellar condensations (PSCs) shows how an initially steep initial mass function (IMF) that might be characteristic primordial cloud fragmentation can change into a Salpeter IMF or shallower in cluster normal density after one dynamical time, even if PSCs are collapsing on their own time. The suggests top‐heavy IMFs some starburst clusters originate with PSC coalescence.

When the gas of a magnetized filamentary cloud obeys polytropic equation state, gravitational collapse is studied using simplified model. We concentrate on radial distribution and restrict ourselves to purely toroidal magnetic field. If axial motions poloidal fields are sufficiently weak, we could reasonably expect our solutions be good approximation. show that while filament experiences condensation density at center increases, flux-to-mass ratio remains constant. A series spatial profiles...

Self-similar and semi-analytical solutions are found for the height-averaged equations govern dynamical behavior of a polytropic, self-gravitating disk under effects winds, around nascent object. In order to describe time evolution system, we adopt radius dependent mass loss rate, then highlight its importance on both traditional $\alpha$ innovative $\beta$ models viscosity prescription. agreement with some other studies, our represent that Toomre parameter is less than one in most regions...

We study the orbit of a pressure-confined cloud in broad-line region (BLR) active galactic nuclei when combined effects central gravity and anisotropic radiation pressure drag force are considered. The physical properties intercloud gas, such as its dynamic viscosity, defined power-law functions radial distance. For proportional to relative velocity background detailed analysis orbits is performed for different values input parameters. also present analytical solutions uniform viscosity...

A model for axisymmetric magnetized accretion flow is proposed. The dominant mechanism of energy dissipation assumed to be the magnetic diffusivity due turbulence in flow. In analogy advection-dominated (ADAF) solutions, a constant fraction resistively dissipated stored accreting gas and rest radiated. We first introduce general self-similar solutions which describe resistive nonrotating with purely poloidal field. radial dependence physical quantities identical that viscous ADAF solutions....

In this paper, steady-state advective accretion flows in the presence of thermal conduction are studied. All three components velocity spherical coordinates considered and flow displays both inflowing outflowing regions according to our similarity solutions. Thermal conductivity provides latitudinal energy transport, so, rotates more slowly becomes hotter with increasing coefficient. We also show that opening angle outflow region decreases as stronger.

We investigate the effects of a large-scale magnetic field with open lines on steady-state structure radiation-dominated accretion disk, using self-similarity technique. The disk is supposed to be turbulent and possesses an effective viscosity diffusivity. consider extreme case in which generated energy due viscous dissipation balanced by advection cooling. While outside treated phenomenological way, internal determined self-consistently. Magnetized nonmagnetized solutions have same radial...

We investigate the linear theory of Kelvin-Helmholtz instability at interface between a partially ionized dusty outflow and ambient material analytically. model interaction as multifluid system in planar geometry. The unstable modes are independent from charge polarity dust particles. Although our results show stabilizing effect for charged particles, growth time scale growing gradually becomes mass or particles when magnetic field strength increases. that decreases with increasing field....

The standard Advection-Dominated Accretion Flow (ADAF) is studied using a set of self-similar analytical solutions in the spherical coordinates. Our new are useful for studying ADAFs without dealing with usual mathematical complexity. We assume $r\varphi$ component stress tensor dominates and latitudinal velocity negligible. Moreover, fluid incompressible radially self-similar. show that our display most important properties which have already been obtained by detailed numerical solutions....

Gravitational stability of a disc consisting the gaseous and stellar components are studied in linear regime when component is turbulent. A phenomenological approach adopted to describe turbulence, which not only effective surface density but velocity dispersion both scale-dependent as power-law functions wavenumber perturbations. Also, has gravitational interaction with gas considered fluid. We calculate growth rate perturbations most cases, highly depends on existence stars exponents for...