53,406 research outputs found
The Core-Collapse Supernova Explosion Mechanism
The explosion mechanism of core-collapse supernovae is a long-standing
problem in stellar astrophysics. We briefly outline the main contenders for a
solution and review recent efforts to model core-collapse supernova explosions
by means of multi-dimensional simulations. We discuss several suggestions for
solving the problem of missing or delayed neutrino-driven explosions in
three-dimensional supernova models, including -- among others -- variations in
the microphysics and large seed perturbations in convective burning shells.
Focusing on the neutrino-driven mechanism, we summarise currents efforts to
predict supernova explosion and remnant properties based on first-principle
models and on more phenomenological approaches.Comment: Invited review to appear in the International Astronomical Union
Proceedings Serie (IAU Symposium 329, "The Lives and Death Throes of Massive
Stars"). 8 pages, 2 figure
Neutrino Emission as Diagnostics of Core-Collapse Supernovae
With myriads of detection events from a prospective Galactic core-collapse
supernova, current and future neutrino detectors will be able to sample
detailed, time-dependent neutrino fluxes and spectra. This offers enormous
possibilities for inferring supernova physics from the various phases of the
neutrino signal from the neutronization burst through the accretion and early
explosion phase to the cooling phase. The signal will constrain the time
evolution of bulk parameters of the young proto-neutron star like its mass and
radius as well as the structure of the progenitor, probe multi-dimensional
phenomena in the supernova core, and constrain thedynamics of the early
explosion phase. Aside from further astrophysical implications, supernova
neutrinos may also shed further light on the properties of matter at
supranuclear densities and on open problems in particle physics.Comment: 26 pages, 5 figures. Accepted for publication in Annual Review of
Nuclear and Particle Science, vol. 69. Non-copyedited version prepared by the
autho
The Status of Multi-Dimensional Core-Collapse Supernova Models
Models of core-collapse supernova explosions powered by the neutrino-driven
mechanism have matured considerable in recent years. Explosions at the low-mass
end of the progenitor spectrum can routinely be simulated in 1D, 2D, and 3D and
allow us to study supernova nucleosynthesis based on first-principle models.
Results of nucleosynthesis calculations indicate that supernovae of the lowest
masses could be important contributors of some lighter n-rich elements beyond
iron. The explosion mechanism of more massive stars is still under
investigation, although first 3D models of neutrino-driven explosions employing
multi-group neutrino transport have recently become available. Together with
earlier 2D models and more simplified 3D simulations, these have elucidated the
interplay between neutrino heating and hydrodynamic instabilities in the
post-shock region that is essential for shock revival. However, some physical
ingredients may still need to be added or improved before simulations can
robustly explain supernova explosions over a wide mass range. We explore
possible issues that may affect the accuracy of supernova simulations, and
review some of the ideas that have recently been explored as avenues to robust
explosions, including uncertainties in the neutrino rates, rapid rotation, and
an external forcing of non-radial fluid motions by strong seed perturbations
from convective shell burning. The perturbation-aided neutrino-driven mechanism
and the implications of recent 3D simulations of shell burning in supernova
progenitors are discussed in detail. The efficacy of the perturbation-aided
mechanism is illustrated by the first successful multi-group neutrino
hydrodynamics simulation of an 18 solar mass progenitor with 3D initial
conditions. We conclude with speculations about the potential impact of 3D
effects on the structure of massive stars through convective boundary mixing.
(abridged)Comment: 30 pages, 7 figures. Invited review for Publications of the
Astronomical Society of Australia, to be published in special issue on
"Electron Capture Supernoave". Accepted version after refereein
Relativistic electron-ion recombination in the presence of an intense laser field
Radiative recombination of a relativistic electron with a highly charged ion
in the presence of an intense laser field is considered. Various relativistic
effects, caused by the high energy of the incoming electron and its strong
coupling to the intense laser field, are found to clearly manifest themselves
in the spectra of the emitted -photons.Comment: 4 papes, 2 figure
Sonic Mach Cones Induced by Fast Partons in a Perturbative Quark-Gluon Plasma
We derive the space-time distribution of energy and momentum deposited by a
fast parton traversing a weakly coupled quark-gluon plasma by treating the fast
part on as the source of an external color field perturbing the medium. We then
use our result as a source term for the linearized hydrodynamical equations of
the medium. We show that the solution contains a sonic Mach cone and a
dissipative wake if the parton moves at a supersonic speed.Comment: Final version accepted for publicatio
Double distributions: Loose ends
We point out that double distributions need not vanish at their boundary.
Boundary terms do not change the ambiguity inherent in defining double
distributions; instead, boundary conditions must be satisfied in order to
switch between different decompositions. We analyze both the spin zero and spin
one-half cases.Comment: 4 pages, 0 figures, RevTex 4, Brief Repor
Resonant two-photon single ionization of two atoms
Resonant two-photon ionization in a system consisting of two spatially
well-separated atoms is studied. Due to two-center electron-electron
correlations, the ionization may also proceed through photo-excitation of both
atoms with subsequent interatomic Coulombic decay. We show that this channel
may dominate the photoionization process and qualitatively change its
dependence on the field intensity and the spectra of emitted electrons.Comment: 4 pages, 4 figure
Non-Radial Instabilities and Progenitor Asphericities in Core-Collapse Supernovae
Since core-collapse supernova simulations still struggle to produce robust
neutrino-driven explosions in 3D, it has been proposed that asphericities
caused by convection in the progenitor might facilitate shock revival by
boosting the activity of non-radial hydrodynamic instabilities in the
post-shock region. We investigate this scenario in depth using 42 relativistic
2D simulations with multi-group neutrino transport to examine the effects of
velocity and density perturbations in the progenitor for different perturbation
geometries that obey fundamental physical constraints (like the anelastic
condition). As a framework for analysing our results, we introduce
semi-empirical scaling laws relating neutrino heating, average turbulent
velocities in the gain region, and the shock deformation in the saturation
limit of non-radial instabilities. The squared turbulent Mach number, ,
reflects the violence of aspherical motions in the gain layer, and explosive
runaway occurs for ~0.3, corresponding to a reduction of the critical
neutrino luminosity by ~25% compared to 1D. In the light of this theory,
progenitor asphericities aid shock revival mainly by creating anisotropic mass
flux onto the shock: Differential infall efficiently converts velocity
perturbations in the progenitor into density perturbations (Delta rho/rho) at
the shock of the order of the initial convective Mach number Ma. The
anisotropic mass flux and ram pressure deform the shock and thereby amplify
post-shock turbulence. Large-scale (l=2,l=1) modes prove most conducive to
shock revival, whereas small-scale perturbations require unrealistically high
convective Mach numbers. Initial density perturbations in the progenitor are
only of order Ma^2 and therefore play a subdominant role.Comment: revised version, 34 pages, 24 figure
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