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Register a new userCosmic Chandlery with Thermonuclear Supernovae
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Thermonuclear (Type Ia) supernovae are bright stellar explosions, the light curves of which can be calibrated to allow for use as standard candles for measuring cosmological distances. Contemporary research investigates how the brightness of an event may be influenced by properties of the progenitor system that follow from properties of the host galaxy such as composition and age. The goals are to better understand systematic effects and to assess the intrinsic scatter in the brightness, thereby reducing uncertainties in cosmological studies. We present the results from ensembles of simulations in the single-degenerate paradigm addressing the influence of age and metallicity on the brightness of an event and compare our results to observed variations of brightness that correlate with properties of the host galaxy. We also present results from hybrid progenitor models that incorporate recent advances in stellar evolution.
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The explosion energy of thermonuclear (Type Ia) supernovae is derived from the difference in nuclear binding energy liberated in the explosive fusion of light fuel nuclei, predominantly carbon and oxygen, into more tightly bound nuclear ash dominated by iron and silicon group elements. The very same explosive thermonuclear fusion event is also one of the major processes contributing to the nucleosynthesis of the heavy elements, in particular the iron-group elements. For example, most of the iron and manganese in the sun and its planetary system were produced in thermonuclear supernovae. Here, we review the physics of explosive thermonuclear burning in carbon-oxygen white dwarf material and the methodologies utilized in calculating predicted nucleosynthesis from hydrodynamic explosion models. While the dominant explosion scenario remains unclear, many aspects of the nuclear combustion and nucleosynthesis are common to all models and must occur in some form in order to produce the observed yields. We summarize the predicted nucleosynthetic yields for existing explosion models, placing particular emphasis on characteristic differences in the nucleosynthetic signatures of the different suggested scenarios leading to Type Ia supernovae. Following this, we discuss how these signatures compare with observations of several individual supernovae, remnants, and the composition of material in our galaxy and galaxy clusters.
We perform binary evolution calculations on helium star - carbon-oxygen white dwarf (CO WD) binaries using the stellar evolution code MESA. This single degenerate channel may contribute significantly to thermonuclear supernovae at short delay times. We examine the thermal-timescale mass transfer from a 1.1 - 2.0 $M_{odot}$ helium star to a 0.90 - 1.05 $M_{odot}$ CO WD for initial orbital periods in the range 0.05 - 1 day. Systems in this range may produce a thermonuclear supernova, helium novae, a helium star - oxygen-neon WD binary, or a detached double CO WD binary. Our time-dependent calculations that resolve the stellar structures of both binary components allow accurate distinction between the eventual formation of a thermonuclear supernova (via central ignition of carbon burning) and that of an ONe WD (in the case of off-center ignition). Furthermore, we investigate the effect of a slow WD wind which implies a specific angular momentum loss from the binary that is larger than typically assumed. We find that this does not significantly alter the region of parameter space over which systems evolve toward thermonuclear supernovae. Our determination of the correspondence between initial binary parameters and the final outcome informs population synthesis studies of the contribution of the helium donor channel to thermonuclear supernovae. In addition, we constrain the orbital properties and observable stellar properties of the progenitor binaries of thermonuclear supernovae and helium novae.
Thermonuclear supernovae (SNe), a subset of which are the highly important SNe Type,Ia, remain one of the more poorly understood phenomena known to modern astrophysics. In recent years, the single degenerate helium (He) donor channel, where a white dwarf star (WD) accretes He-rich matter from a hydrogen-depleted companion, has emerged as a promising candidate progenitor scenario for these events. An unresolved question in this scenario is the fate of the companion star, which would be evident as a runaway hot subdwarf (He sdO/B) in the aftermath of the SN event. Previous studies have shown that the kinematic properties of an ejected companion provide an opportunity to closer examination of the properties of an SN progenitor system. However, with the number of observed objects not matching predictions by theory, the viability of this mechanism is called into question. In this study, we first synthesize a population of companion stars ejected by the aforementioned mechanism, taking into account predicted ejection velocities, inferred population density in the Galactic (Gal.) mass distribution and subsequent kinematics in the Gal. potential. We then discuss the astrometric properties of this population. We present $10^{6}$ individual ejection trajectories, numerically computed with a newly developed, lightweight simulation framework. A peak in the density distribution for close objects is expected in the direction of the Gal. center. If the entire considered mass range is realized, the radial velocity distribution should show a peak at 500kms. If only close US,708 analogues are considered, there should be a peak at ($sim750-850$)kms. We show that the puzzling lack of confirmed surviving companion stars of thermonuclear SNe, though possibly an observation-related selection effect, may indicate a selection against high mass donors in the SD He donor channel. (-abridged-)
(Abridged) The explosion mechanism of electron-capture supernovae (ECSNe) remains equivocal. We attempt to constrain the explosion mechanism (neutron-star-forming implosion or thermonuclear explosion) and the frequency of occurrence of ECSNe using nucleosynthesis simulations of the latter scenario, population synthesis, the solar abundance distribution, pre-solar meteoritic oxide grain isotopic ratio measurements and the white dwarf mass-radius relation. Tracer particles from 3d hydrodynamic simulations were post-processed with a large nuclear reaction network in order to determine the complete compositional state of the bound ONeFe remnant and the ejecta, and population synthesis simulations were performed in order to estimate the ECSN rate with respect to the CCSN rate. The 3d deflagration simulations drastically overproduce the neutron-rich isotopes $^{48}$Ca, $^{50}$Ti, $^{54}$Cr, $^{60}$Fe and several of the Zn isotopes relative to their solar abundances. Using the solar abundance distribution as our constraint, we place an upper limit on the frequency of thermonuclear ECSNe as 1$-$3~% the frequency at which core-collapse supernovae (FeCCSNe) occur. This is on par with or 1~dex lower than the estimates for ECSNe from single stars. The upper limit from the yields is also in relatively good agreement with the predictions from our population synthesis simulations. The $^{54}$Cr/$^{52}$Cr and $^{50}$Ti/$^{48}$Ti isotopic ratios in the ejecta are a near-perfect match with recent measurements of extreme pre-solar meteoritc oxide grains, and $^{53}$Cr/$^{52}$Cr can also be matched if the ejecta condenses before mixing with the interstellar medium. Theoretical mass-radius relations for the bound ONeFe WD remnants of these explosions are apparently consistent with several observational WD candidates.
We present simulations of thermonuclear supernovae admixed with an extended component of fermionic cold dark matter. We consider the explosion of a Chandrasekhar-mass white dwarf using the deflagration model with deflagration-detonation transition with spherical symmetry. The dark matter component is comparable in size with that of the normal matter, and so the system is described by two-fluid, one-dimensional Eulerian hydrodynamics. The explosion leaves all the dark matter trapped as a remnant compact dark star in all of our considered models. The presence of dark matter lengthens the deflagration phase to produce more thermo-neutrinos and similar amounts of iron-group elements compared to those of ordinary explosions with no dark matter admixture. The dark matter admixed models produce dimmer and broader light curves, which challenge the role of thermonuclear supernovae as standard candles in cosmic distance measurement. Our results also suggest a formation path of dark compact objects which mimic sub-solar-mass black holes as dark gravitational sources, through near-solar-mass dark matter admixed thermonuclear supernovae.
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