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A model of protostar formation under two current carrying gas filaments collision is presented. The model implies MHD approach involving self-gravity and radiative cooling effects. We suppose that through the current carrying gas filament collision a magnetic field reconnection takes place. Using an appropriate self-consistent presentation for time and special dependences of physical quantities in MHD equations, we derive the full set of equations that describes time evolution of the physical quantities just after an occurrence of magnetic field reconnection. Numerical simulations reveal that the process consists of three main phases of evolution. The first is an appearance of preceding peaks in time profiles of density and temperature following by the next phase of depression of both temperature and density and the final fast condensation phase with either cooling or heating of matter depending on initial parameters of problem. Effects of initial conditions like as magnetic field strength, current strength, initial gravity energy, cooling time and a geometry of collision are investigated. Main conclusion is that protostar formation takes place within the time interval less than one free fall time and it is preceded by the appearance of dense and hot matter with lifetime much less than free fall time. The final temperature of the protostar depends on the physical conditions and mainly on the ratio between free fall time and cooling time in the colliding current carrying gas filaments. 相似文献
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We investigate the physical processes occurring in the supergranule boundary cylinder layer (SBCL). Taking into account the Coriolis force, we obtain an expression for the component of the magnetic field and velocity in the SBCL. Within the framework of linear MHD, we consider the formation and coalescence of magnetic tubes, i.e. spicules, in the course of the reconnection of the SBCL magnetic field. The estimated number of spicules appearing on each supergranule cell is in agreement with observations. This number depends on the solar latitude : (1) if the normal component of the magnetic fieldB
z
is assumed to be independent of , then the maximum number of spicules should be at = 71°; (2) ifB
z
is assumed to be the component of the dipolar fieldB
z
sin , then the maximum number should be at the pole: = 90°. The timescale of the formation and the coalescence of the magnetic tubes is 10–20 min, which is of the order of the observed lifetime of the spicules. 相似文献
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M.?Sh.?GigolashviliEmail author D.?R.?Japaridze T.?G.?Mdzinarishvili B.?B.?Chargeishvili 《Solar physics》2005,227(1):27-38
The properties of the differential rotation of the Sun are investigated by using H filaments as tracers. Annual average angular velocities of 716 quiescent filaments are determined from H photoheliograms of the Abastumani Astrophysical Observatory film collection for the years 1957–1993. The existence of north-south (N–S) asymmetry in H filaments rotation is confirmed statistically. The connection of asymmetry with the solar activity cycles is established. It is found that the northern hemisphere rotates faster during the even cycles (20 and 22) while the rotation of southern hemisphere dominates in odd ones (cycles 19 and 21). The mechanism of the solar activity should be responsible for the N–S asymmetry of the solar differential rotation. A theoretical explanation for the N–S asymmetry in the Suns rotation is offered. It is suggested that the asymmetry in the rotation of the two hemispheres of the Sun is balanced by the dynamo mechanism, which acts in parallel to the mechanism offered here. It is concluded that the N–S asymmetry of the solar rotation should cause a difference in activity level between the northern and southern hemispheres. 相似文献
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Bidzina Z. Kapanadze 《Astrophysics and Space Science》2012,337(1):343-351
This paper presents a modeling of the variable synchrotron emission in the BL Lacertae sources (BLLs). Flux variability is
assumed to be a result of the interaction between a relativistic shock wave with a magnetized jet material. Long-term flares
(of months to years durations) are modeled via the propagation of a plane relativistic shock wave though the emission zone
of a cylindrical form with the radius R and length H. As for short-term bursts (lasting from days to weeks), they may result from shock passage through the jet inhomogeneities
such as a shell of enhanced density downstream to a Mach disc, originated due to pressure imbalance between the jet and its
ambient medium. Emitting particles (electrons) gain the energies, sufficient to produce synchrotron photons at optical—X-ray
frequencies, via the first-order Fermi mechanism. Observation’s frequency is the main parameter determining a rate of the
increase/ decay of the emission via the characteristic decay time of emitting electrons. The magnetic field, assumed to be
turbulent with an average field constant throughout the entire emission zone, is another key parameter determining the slope
of a lightcurve corresponding to the flare—the higher strength the magnetic field has, the steeper the lightcurve is. The
rest input parameters (shock speed, jet viewing angle, maximum/minimum energies of the electrons, particles’ density etc.),
as well the strength of average magnetic field, influence the energy output from a flare. 相似文献
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A model of two-current-loop collisions is presented to explain the impulsive nature of solar flares. From MHD equations considering the gravity and resistivity effects we find self-consistent expressions and a set of equations governing the behavior of all physical quantities just after magnetic reconnection has taken place. Numerical simulations have revealed that the most important parameters of the problem are the plasma and the ratio of initial values of pressure gradient in the longitudinal and radial directions. Thus, the low plasma case during aY-type interaction (initial longitudinal pressure gradient is comparable with initial radial pressure gradient) shows a rapid pinch and simultaneous enhancement of all physical quantities, including the electric field components, which are important for high-energy particle acceleration. However, an increase of the plasma causes a weakening of the pinch effect and a decrease of extreme values of all physical quantities. On the other hand, for anX-type collision (initial longitudinal pressure gradient is much greater than initial radial pressure gradient), which is able to provide a jet, the increase of the plasma causes a high velocity jet. As for aI-type collision (initial longitudinal pressure gradient is much less than initial radial pressure gradient) it shows neither jet production nor very strong enhancement of physical quantities. We also consider direct and oblique collisions, taking into account both cases of partial and complete reconnection. 相似文献