825 research outputs found
Multidimensional Simulations of Rotating Pair Instability Supernovae
We study the effects of rotation on the dynamics, energetics and Ni-56
production of Pair Instability Supernova explosions by performing rotating
two-dimensional ("2.5-D") hydrodynamics simulations. We calculate the evolution
of eight low metallicity (Z = 10^-3, 10^-4 Zsun) massive (135-245 Msun) PISN
progenitors with initial surface rotational velocities 50% that of the critical
Keplerian value using the stellar evolution code MESA. We allow for both the
inclusion and the omission of the effects of magnetic fields in the angular
momentum transport and in chemical mixing, resulting in slowly-rotating and
rapidly-rotating final carbon-oxygen cores, respectively. Increased rotation
for carbon-oxygen cores of the same mass and chemical stratification leads to
less energetic PISN explosions that produce smaller amounts of Ni-56 due to the
effect of the angular momentum barrier that develops and slows the dynamical
collapse. We find a non-monotonic dependence of Ni-56 production on rotational
velocity in situations when smoother composition gradients form at the outer
edge of the rotating cores. In these cases, the PISN energetics are determined
by the competition of two factors: the extent of chemical mixing in the outer
layers of the core due to the effects of rotation in the progenitor evolution
and the development of angular momentum support against collapse. Our 2.5-D
PISN simulations with rotation are the first presented in the literature. They
reveal hydrodynamic instabilities in several regions of the exploding star and
increased explosion asymmetries with higher core rotational velocity.Comment: 31 pages, 23 figures, accepted for publication in the Ap
Gas Dynamics of the Nickel-56 Decay Heating in Pair-Instability Supernovae
Very massive 140-260 Msun stars can die as highly-energetic pair-instability
supernovae (PI SNe) with energies of up to 100 times those of core-collapse SNe
that can completely destroy the star, leaving no compact remnant behind. These
explosions can synthesize Msun of radioactive Ni56, which can cause
them to rebrighten at later times when photons due to Ni56 decay diffuse out of
the ejecta. However, heat from the decay of such large masses of Ni56 could
also drive important dynamical effects deep in the ejecta that are capable of
mixing elements and affecting the observational signatures of these events. We
have now investigated the dynamical effect of Ni56 heating on PI SN ejecta with
high-resolution two-dimensional hydrodynamic simulations performed with the
CASTRO code. We find that expansion of the hot Ni56 bubble forms a shell at the
base of the silicon layer of the ejecta about 200 days after the explosion but
that no hydrodynamical instabilities develop that would mix Ni56 with the
Si/O-rich ejecta. However, while the dynamical effects of Ni56 heating may be
weak they could affect the observational signatures of some PI SNe by diverting
decay energy into internal expansion of the ejecta at the expense of
rebrightening at later times.Comment: Accepted to ApJ, 14 page
Pair Instability Supernovae of Very Massive Population III Stars
Numerical studies of primordial star formation suggest that the first stars
in the universe may have been very massive. Stellar models indicate that
non-rotating Population III stars with initial masses of 140-260 Msun die as
highly energetic pair-instability supernovae. We present new two-dimensional
simulations of primordial pair-instability supernovae done with the CASTRO
code. Our simulations begin at earlier times than previous multidimensional
models, at the onset of core collapse, to capture any dynamical instabilities
that may be seeded by collapse and explosive burning. Such instabilities could
enhance explosive yields by mixing hot ash with fuel, thereby accelerating
nuclear burning, and affect the spectra of the supernova by dredging up heavy
elements from greater depths in the star at early times. Our grid of models
includes both blue supergiants and red supergiants over the range in progenitor
mass expected for these events. We find that fluid instabilities driven by
oxygen and helium burning arise at the upper and lower boundaries of the oxygen
shell 20 - 100 seconds after core bounce. Instabilities driven by
burning freeze out after the SN shock exits the helium core. As the shock later
propagates through the hydrogen envelope, a strong reverse shock forms that
drives the growth of Rayleigh--Taylor instabilities. In red supergiant
progenitors, the amplitudes of these instabilities are sufficient to mix the
supernova ejecta.Comment: 42 pages, 15 figures (accepted to ApJ
Multi-Dimensional Simulations of Pair-Instability Supernovae
We present preliminary results from multidimensional numerical studies of
pair instability supernova (PSN), studying the fluid instabilities that occur
in multiple spatial dimensions. We use the new radiation-hydrodynamics code,
CASTRO, and introduce a new mapping procedure that defines the initial
conditions for the multidimensional runs in such a way that conservation of
physical quantities is guaranteed at any level of resolution.Comment: Accepted for publication in Computer Physics Communications. 3 pages.
2 fig
Two Dimensional Simulations of Pair-Instability Supernovae
We present preliminary results from two dimensional numerical studies of pair
instability supernova (PSN). We study nuclear burning, hydrodynamic
instabilities and explosion of very massive stars. Use a new
radiation-hydrodynamics code, CASTRO.Comment: Proceedings of "The First Stars and Galaxies: Challenges for the Next
Decade", Austin, Texas, March 8-11, 2010. 2 pages, 1 figur
Explosive Nucleosynthesis: Prospects
Explosive nucleosynthesis is a combination of the nuclear physics of
thermonuclear reactions, and the hydrodynamics of the plasma in which the
reactions occur. It depends upon the initial conditions---the stellar evolution
up to the explosive instability, and the nature of the explosion mechanism.
Some key issues for explosive nucleosynthesis are the interaction of burning
with hydrodynamics, the degree of microscopic mixing in convective zones, and
the breaking of spherical symmetry by convection and rotation. Recent
experiments on high intensity lasers provides new opportunities for laboratory
testing of astrophysical hydrodynamic codes. Implications of SN1987A, SN1998bw
(GRB980425?), and eta Carina are discussed, as well as the formation of black
holes or neutron stars.Comment: 15 pages, no figures, Elsevier Science volume honoring David N.
Schram
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