768 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
The Proto-neutron Star Phase of the Collapsar Model and the Route to Long-soft Gamma-ray Bursts and Hypernovae
Recent stellar evolutionary calculations of low-metallicity massive
fast-rotating main-sequence stars yield iron cores at collapse endowed with
high angular momentum. It is thought that high angular momentum and black hole
formation are critical ingredients of the collapsar model of long-soft
gamma-ray bursts (GRBs). Here, we present 2D multi-group,
flux-limited-diffusion MHD simulations of the collapse, bounce, and immediate
post-bounce phases of a 35-Msun collapsar-candidate model of Woosley & Heger.
We find that, provided the magneto-rotational instability (MRI) operates in the
differentially-rotating surface layers of the millisecond-period neutron star,
a magnetically-driven explosion ensues during the proto-neutron star phase, in
the form of a baryon-loaded non-relativistic jet, and that a black hole,
central to the collapsar model, does not form. Paradoxically, and although much
uncertainty surrounds stellar mass loss, angular momentum transport, magnetic
fields, and the MRI, current models of chemically homogeneous evolution at low
metallicity yield massive stars with iron cores that may have too much angular
momentum to avoid a magnetically-driven, hypernova-like, explosion in the
immediate post-bounce phase. We surmise that fast rotation in the iron core may
inhibit, rather than enable, collapsar formation, which requires a large
angular momentum not in the core but above it. Variations in the angular
momentum distribution of massive stars at core collapse might explain both the
diversity of Type Ic supernovae/hypernovae and their possible association with
a GRB. A corollary might be that, rather than the progenitor mass, the angular
momentum distribution, through its effect on magnetic field amplification,
distinguishes these outcomes.Comment: 5 pages, 1 table, 2 figures, accepted to ApJ
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
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
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