1,923 research outputs found
Massive Computation for Understanding Core-Collapse Supernova Explosions
How do massive stars explode? Progress toward the answer is driven by increases in compute power. Petascale supercomputers are enabling detailed 3D simulations of core-collapse supernovae that are elucidating the role of fluid instabilities, turbulence, and magnetic field amplification in supernova engines
Massive Computation for Understanding Core-Collapse Supernova Explosions
How do massive stars explode? Progress toward the answer is driven by increases in compute power. Petascale supercomputers are enabling detailed 3D simulations of core-collapse supernovae that are elucidating the role of fluid instabilities, turbulence, and magnetic field amplification in supernova engines
Compact Remnant Mass Function: Dependence on the Explosion Mechanism and Metallicity
The mass distribution of neutron stars and stellar-mass black holes provides
vital clues into the nature of stellar core collapse and the physical engine
responsible for supernova explosions. Using recent advances in our
understanding of supernova engines, we derive mass distributions of stellar
compact remnants. We provide analytical prescriptions for compact object masses
for major population synthesis codes. In an accompanying paper, Belczynski et
al., we demonstrate that these qualitatively new results for compact objects
can explain the observed gap in the remnant mass distribution between ~2-5
solar masses and that they place strong constraints on the nature of the
supernova engine. Here, we show that advanced gravitational radiation detectors
(like LIGO/VIRGO or the Einstein Telescope) will be able to further test the
supernova explosion engine models once double black hole inspirals are
detected.Comment: 37 pages with 16 figures, submitted to Ap
Cosmic Explosions: Rapporteur Summary of the 10th Maryland Astrophysics Conference
This meeting covered the range of cosmic explosions from solar flares to
gamma-ray bursts. A common theme is the role of rotation and magnetic fields. A
rigorous examination is underway to characterize systematic effects that might
alter the Type Ia supernova results suggesting an accelerating Universe. The
discovery of the central point of X-ray emission in Cas A by CXO should give
new insight into the core collapse problem in general and the nature of the
still undetected compact remnant in SN 1987A in particular. Jets were described
from protostars to microquasars to blazars to gamma-ray bursts. Polarization
studies of core-collapse supernovae lead to the conclusion that core collapse
is not merely asymmetric, but strongly bi-polar. To account for normal
core-collapse supernovae, the explosion must be jet-like in routine
circumstances, that is, in the formation of neutron stars, not only for black
holes. Given the observed asymmetries, estimates of explosion energies based on
spherically-symmetric models must be regarded with caution. The strong
possibility that at least some gamma-ray bursts arise from massive stars means
that it is no longer possible to decouple models of the gamma-ray burst and
afterglow from considerations of the "machine." The implied correlation of
gamma-ray bursts with star formation and massive stars and evidence for jets
does not distinguish a black hole collapsar model from models based on the
birth of a magnetar. Calorimetry of at least one afterglow suggests that
gamma-ray bursts cannot involve highly inefficient internal shock models.
Essentally all gamma-ray burst models involve the "Blandford Anxiety," the
origin of nearly equipartition magnetic fields in the associated relativistic
shocks.Comment: 22 pages LaTeX, one eps figure, to be published in the Proceedings of
the 10th Maryland Conference on Astrophysics, eds, S. Holt and W. Zhang, AI
Inferring Core-Collapse Supernova Physics with Gravitational Waves
Stellar collapse and the subsequent development of a core-collapse supernova
explosion emit bursts of gravitational waves (GWs) that might be detected by
the advanced generation of laser interferometer gravitational-wave
observatories such as Advanced LIGO, Advanced Virgo, and LCGT. GW bursts from
core-collapse supernovae encode information on the intricate multi-dimensional
dynamics at work at the core of a dying massive star and may provide direct
evidence for the yet uncertain mechanism driving supernovae in massive stars.
Recent multi-dimensional simulations of core-collapse supernovae exploding via
the neutrino, magnetorotational, and acoustic explosion mechanisms have
predicted GW signals which have distinct structure in both the time and
frequency domains. Motivated by this, we describe a promising method for
determining the most likely explosion mechanism underlying a hypothetical GW
signal, based on Principal Component Analysis and Bayesian model selection.
Using simulated Advanced LIGO noise and assuming a single detector and linear
waveform polarization for simplicity, we demonstrate that our method can
distinguish magnetorotational explosions throughout the Milky Way (D <~ 10kpc)
and explosions driven by the neutrino and acoustic mechanisms to D <~ 2kpc.
Furthermore, we show that we can differentiate between models for rotating
accretion-induced collapse of massive white dwarfs and models of rotating iron
core collapse with high reliability out to several kpc.Comment: 22 pages, 9 figure
Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks
A series of numerical simulations on magnetorotational core-collapse
supernovae are carried out. Dipole-like configurations which are offset
northward are assumed for the initially strong magnetic fields together with
rapid differential rotations. Aims of our study are to investigate effects of
the offset magnetic field on magnetar kicks and on supernova dynamics. Note
that we study a regime where the proto-neutron star formed after collapse has a
large magnetic field strength approaching that of a ``magnetar'', a highly
magnetized slowly rotating neutron star. As a result, equatorially-asymmetric
explosions occur with a formation of the bipolar jets. Resultant magnetar's
kick velocities are km s. We find that the acceleration
is mainly due to the magnetic pressure while the somewhat weaker magnetic
tension works toward the opposite direction, which is due to stronger magnetic
field in the northern hemisphere. Noted that observations of magnetar's proper
motions are very scarce, our results supply a prediction for future
observations. Namely, magnetars possibly have large kick velocities, several
hundred km s, as ordinary neutron stars do, and in an extreme case they
could have those up to 1000 km s.Comment: 36 pages, 9 figures, accepted by the Astrophysical Journa
Core Collapse and Then? The Route to Massive Star Explosions
The rapidly growing base of observational data for supernova explosions of
massive stars demands theoretical explanations. Central of these is a
self-consistent model for the physical mechanism that provides the energy to
start and drive the disruption of the star. We give arguments why the delayed
neutrino-heating mechanism should still be regarded as the standard paradigm to
explain most explosions of massive stars and show how large-scale and even
global asymmetries can result as a natural consequence of convective overturn
in the neutrino-heating region behind the supernova shock. Since the explosion
is a threshold phenomenon and depends sensitively on the efficiency of the
energy transfer by neutrinos, even relatively minor differences in numerical
simulations can matter on the secular timescale of the delayed mechanism. To
enhance this point, we present some results of recent one- and two-dimensional
computations, which we have performed with a Boltzmann solver for the neutrino
transport and a state-of-the-art description of neutrino-matter interactions.
Although our most complete models fail to explode, the simulations demonstrate
that one is encouragingly close to the critical threshold because a modest
variation of the neutrino transport in combination with postshock convection
leads to a weak neutrino-driven explosion with properties that fulfill
important requirements from observations.Comment: 14 pages; 3 figures. Invited Review, in: ``From Twilight to
Highlight: The Physics of Supernovae'', Eds. W. Hillebrandt and B.
Leibundgut, Springer Series ``ESO Astrophysics Symposia'', Berli
Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks
A series of numerical simulations on magnetorotational core-collapse
supernovae are carried out. Dipole-like configurations which are offset
northward are assumed for the initially strong magnetic fields together with
rapid differential rotations. Aims of our study are to investigate effects of
the offset magnetic field on magnetar kicks and on supernova dynamics. Note
that we study a regime where the proto-neutron star formed after collapse has a
large magnetic field strength approaching that of a ``magnetar'', a highly
magnetized slowly rotating neutron star. As a result, equatorially-asymmetric
explosions occur with a formation of the bipolar jets. Resultant magnetar's
kick velocities are km s. We find that the acceleration
is mainly due to the magnetic pressure while the somewhat weaker magnetic
tension works toward the opposite direction, which is due to stronger magnetic
field in the northern hemisphere. Noted that observations of magnetar's proper
motions are very scarce, our results supply a prediction for future
observations. Namely, magnetars possibly have large kick velocities, several
hundred km s, as ordinary neutron stars do, and in an extreme case they
could have those up to 1000 km s.Comment: 36 pages, 9 figures, accepted by the Astrophysical Journa
Core-Collapse Supernovae: Reflections and Directions
Core-collapse supernovae are among the most fascinating phenomena in
astrophysics and provide a formidable challenge for theoretical investigation.
They mark the spectacular end of the lives of massive stars and, in an
explosive eruption, release as much energy as the sun produces during its whole
life. A better understanding of the astrophysical role of supernovae as birth
sites of neutron stars, black holes, and heavy chemical elements, and more
reliable predictions of the observable signals from stellar death events are
tightly linked to the solution of the long-standing puzzle how collapsing stars
achieve to explode. In this article our current knowledge of the processes that
contribute to the success of the explosion mechanism are concisely reviewed.
After a short overview of the sequence of stages of stellar core-collapse
events, the general properties of the progenitor-dependent neutrino emission
will be briefly described. Applying sophisticated neutrino transport in
axisymmetric (2D) simulations with general relativity as well as in simulations
with an approximate treatment of relativistic effects, we could find successful
neutrino-driven explosions for a growing set of progenitor stars. First results
of three-dimensional (3D) models have been obtained, and magnetohydrodynamic
simulations demonstrate that strong initial magnetic fields in the pre-collapse
core can foster the onset of neutrino-powered supernova explosions even in
nonrotating stars. These results are discussed in the context of the present
controversy about the value of 2D simulations for exploring the supernova
mechanism in realistic 3D environments, and they are interpreted against the
background of the current disagreement on the question whether the standing
accretion shock instability (SASI) or neutrino-driven convection is the crucial
agency that supports the onset of the explosion.Comment: 36 pages, 20 figures (43 eps files); submitted to Progress of
Theoretical and Experimental Physics (PTEP
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