463 research outputs found
Jet Formation from Rotating Magnetized Objects
Jet formation is connected most probably with matter acceleration from the
vicinity of rotating magnetized bodies. It is usually related to the mass
outflows and ejection from accretion disks around black holes. Problem of jet
collimation is discussed. Collapse of a rotating magnetized body during star
formation or supernovae explosion may lead to a jet-like mass ejection for
certain angular velocity and magnetic field distributions at the beginning of
the collapse. Jet formation during magnetorotational explosion is discussed
basing on the numerical simulation of collapse of magnetized bodied with
quasi-dipole field.Comment: Will be published in the proc. of 20th Texas Symposium, Austin, Texas
7 pages, 7 picture
Electromagnetohydrodynamics
Interaction of plasma flow with a magnetic obstacle is a frequent process in
many laser-plasma experiments in the laboratory, and is an important event in
many astrophysical objects such as X-ray pulsars, AGN, GRB etc. As a result of
plasma penetration through the magnetic wall we could expect a formation of
magnetohydrodynamic (MHD) shock waves, as well as of electromagnetic (EM) ones.
To study these processes we need equations following from hydrodynamic and
Maxwell equations, which in the limiting situations describe MHD and EM waves,
and are valid for the general case, when both phenomena are present. Here we
derive a set of equations following from hydrodynamic and Maxwell equations,
without neglecting a displacement current, needed for a formation of EM waves.
We find a dispersion equation describing a propagation of a weak linear wave in
a magnetized plasma along the axis, perpendicular to the magnetic field
, which contains MHD, hydrodynamic and EM waves in the limiting cases,
and some new types of behaviour in a general situation. We consider a plasma
with zero viscosity and heat conductivity, but with a finite electric
conductivity with a scalar coefficient.Comment: 8 papers, 8 figures, 1 table, to be submitted in PR
Alfven Wave-Driven Supernova Explosion
We investigate the role of Alfven waves in the core-collapse supernova (SN)
explosion. We assume that Alfven waves are generated by convections inside a
proto-neutron star (PNS) and emitted from its surface. Then these waves
propagate outwards, dissipate via nonlinear processes, and heat up matter
around a stalled prompt shock. To quantitatively assess the importance of this
process for the revival of the stalled shock, we perform 1D time-dependent
hydrodynamical simulations, taking into account the heating via the dissipation
of Alfven waves that propagate radially outwards along open flux tubes. We show
that the shock revival occurs if the surface field strength is larger than
~2e15 G and if the amplitude of velocity fluctuation at the PNS surface is
larger than 20% of the local sound speed. Interestingly, the Alfven wave
mechanism is self-regulating in the sense that the explosion energy is not very
sensitive to the surface field strength and initial amplitude of Alfven waves
as long as they are larger than the threshold values given above.Comment: 7 pages, 3 figures embedded, submitted to Ap
Magnetorotational supernovae
We present the results of 2D simulations of the magnetorotational model of a
supernova explosion. After the core collapse the core consists of rapidly a
rotating proto-neutron star and a differentially rotating envelope. The
toroidal part of the magnetic energy generated by the differential rotation
grows linearly with time at the initial stage of the evolution of the magnetic
field. The linear growth of the toroidal magnetic field is terminated by the
development of magnetohydrodynamic instability, leading to drastic acceleration
in the growth of magnetic energy. At the moment when the magnetic pressure
becomes comparable with the gas pressure at the periphery of the proto-neutron
star km from the star centre the MHD compression wave appears and
goes through the envelope of the collapsed iron core. It transforms soon to the
fast MHD shock and produces a supernova explosion. Our simulations give the
energy of the explosion ergs. The amount of the mass ejected
by the explosion is . The implicit numerical method, based on
the Lagrangian triangular grid of variable structure, was used for the
simulations.Comment: Revised version. Submitted to the MNRA
Cosmic Rays from PeV to ZeV, Stellar Evolution, Supernova Physics and Gamma Ray Bursts
The recent success of a proposal from some time ago to explain the spectrum of cosmic rays allows some strong conclusions to be made on the physics of supernovae: In the context of this specific proposal to explain the origin of cosmic rays, the mechanism for exploding supernovae of high mass has to be the one proposed by Bisnovatyi-Kogan more than 30 years ago, which was then based on a broader suggestion by Kardashev: A combination of the effects of rotation and magnetic fields explodes the star. Interestingly, this step then leads inevitably to some further suggestions, useful perhaps for the study of gamma ray bursts and the search of a bright standard candle in cosmology
- …