3,398 research outputs found
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
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
Cosmological Impact Of Population III Binaries
We present the results of the stellar feedback from Population III (Pop III) binaries by employing improved, more realistic Pop III evolutionary stellar models. To facilitate a meaningful comparison, we consider a fixed mass of 60 M-circle dot incorporated in Pop III stars, either contained in a single star, or split up in binary stars of 30 M-circle dot each or an asymmetric case of one 45 and one 15 M-circle dot star. Whereas the sizes of the resulting H II regions are comparable across all cases, the He III regions around binary stars are significantly smaller than that of the single star. Consequently, the He+ 1640 angstrom recombination line is expected to become much weaker. Supernova (SN) feedback exhibits great variety due to the uncertainty in possible explosion pathways. If at least one of the component stars dies as a hypernova about 10 times more energetic than conventional core-collapse SNe, the gas inside the host minihalo is effectively blown out, chemically enriching the intergalactic medium (IGM) to an average metallicity of 10(-4)-10(-3) Z(circle dot), out to similar to 2 kpc. The single star, however, is more likely to collapse into a black hole, accompanied by at most very weak explosions. The effectiveness of early chemical enrichment would thus be significantly reduced, in contrast to. the lower mass binary stars, where at least one component is likely to contribute to heavy element production and dispersal. Important new feedback physics is also introduced if close binaries can form high-mass X-ray binaries, leading to the pre-heating and -ionization of the IGM beyond the extent of the stellar H II regions.IAU-Gruber FellowshipStanwood Johnston FellowshipKITP Graduate FellowshipDOE HEP Program DE-SC0010676NSF AST 0909129, AST-1009928, AST-1109394, PHY02-16783NASA Theory Program NNX14AH34GNASA NNX09AJ33GARC Future Fellowship FT120100363Monash University Larkins FellowshipDOE DE-GF02-87ER40328, DE-FC02-09ER41618Astronom
Radiation Transport Simulations of Pulsational Pair-Instability Supernovae
Massive stars of helium cores of 35-65 Msun eventually encounter the
electron/positron creation instability, and it triggers explosive carbon or
oxygen burning that produces several thermonuclear eruptions. The resulting
catastrophe collisions of eruptive shells sometimes produce luminous transients
with peak luminosity of erg/sec, known as pulsational
pair-instability supernovae (PPISNe). Previous 2D simulations of colliding
shells show the development of Rayleigh-Taylor (RT) instabilities and mixing.
Here we present radiation hydrodynamic PPISNe simulations of a 110 Msun
solar-metallicity star that was promising to produce a superluminous transit in
the early work. Our comprehensive study contains a suite of one-, two-, and
three-dimensional models. We discuss the impact of dimensionality and fluid
instabilities on the resulting light curves. The results show the RT mixing
found in previous multidimensional hydro studies transforms into a thin and
distorted shell due to radiative cooling. Radiation from the wiggly shell peaks
at its bolometric light curve of erg/sec, lasting about
150 days and following with a plateau of erg/sec for
another two hundred days before it fades away. The total radiation energy
emitted from colliding shells is erg, which is of the kinetic energy of the major eruption. The dimensional effects also
manifest on the physical properties, such as irregularity and thickness of the
shell. Our study suggests PPISNe is a promising candidate of luminous SNe, the
radiation of which originates from colliding shells with a homogeneous mixing
of ejecta.Comment: Submitted to ApJ, 16 pages, comments are welcom
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
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