Nucleosynthesis In Core-collapse Supernovae Research Articles

The γ-process nucleosynthesis in core-collapse supernovae II. Effect of the explosive recipe

The process in core-collapse supernovae (CCSNe) can produce a number of neutron-deficient stable isotopes heavier than iron ( nuclei). However, current model predictions do not fully reproduce solar abundances, especially for Mo and Ru We investigate the impact of different explosion energies and parametrizations on the nucleosynthesis of nuclei, by studying stellar models with different initial masses and different CCSN explosions. We compared the yields obtained using a semi-analytical method to simulate the supernova to those obtained using hydrodynamic models. We explored the effect of varying the explosion parameters on the production in two sets of CCSN models with initial masses of 15, 20, and 25 at solar metallicity. We calculated a new set of 24 CCSN models (eight for each stellar progenitor mass) and compared our results with another recently published set of 80 CCSN models that includes a wide range of explosion parameters: explosion energy or initial shock velocity, energy injection time, and mass location of the injection. We find that the total yields are only marginally affected by the CCSN explosion prescriptions if the production is already efficient in the stellar progenitors due to a C–O shell merger. In most CCSN explosions from progenitors without a C-O shell merger, the yields increase with the explosion energy by up to an order of magnitude, depending on the progenitor structure and the CCSN prescriptions. The general trend of the production with the explosion energy is more complicated if we look at the production of single nuclei. The light tend to be the most enhanced with increasing explosion energy. In particular, for the CCSN models where the freeze-out component is ejected, the yields of the lightest nuclei (including Mo and Ru ) increase by up to three orders of magnitude. We provide the first extensive study using different sets of massive stars of the impact of varying CCSN explosion prescriptions on the production of nuclei. Unlike previous expectations and recent results in the literature, we find that the average production of nuclei tends to increase with the explosion energy. We also confirm that the pre-explosion production of nuclei in C-O shell mergers is a robust result, independent of the subsequent explosive nucleosynthesis. More generally, a realistic range of variations in the evolution of stellar progenitors and in the CCSN explosions might boost the CCSN contribution to the galactic chemical evolution of nuclei.

The γ-process nucleosynthesis in core-collapse supernovae

Context. The γ-process nucleosynthesis in core-collapse supernovae is generally accepted as a feasible process for the synthesis of neutron-deficient isotopes beyond iron. However, crucial discrepancies between theory and observations still exist: the average yields of γ-process nucleosynthesis from massive stars are still insufficient to reproduce the solar distribution in galactic chemical evolution calculations, and the yields of the Mo and Ru isotopes are a factor of ten lower than the yields of the other γ-process nuclei. Aims. We investigate the γ-process in five sets of core-collapse supernova models published in the literature with initial masses of 15, 20, and 25 M⊙ at solar metallicity. Methods. We compared the γ-process overproduction factors from the different models. To highlight the possible effect of nuclear physics input, we also considered 23 ratios of two isotopes close to each other in mass relative to their solar values. Further, we investigated the contribution of C–O shell mergers in the supernova progenitors as an additional site of the γ-process. Results. Our analysis shows that a large scatter among the different models exists for both the γ-process integrated yields and the isotopic ratios. We find only ten ratios that agree with their solar values, all the others differ by at least a factor of three from the solar values in all the considered sets of models. The γ-process within C–O shell mergers mostly influences the isotopic ratios that involve intermediate and heavy proton-rich isotopes with A > 100. Conclusions. We conclude that there are large discrepancies both among the different data sets and between the model predictions and the solar abundance distribution. More calculations are needed; particularly updating the nuclear network, because the majority of the models considered in this work do not use the latest reaction rates for the γ-process nucleosynthesis. Moreover, the role of C–O shell mergers requires further investigation.

Measurements of the Zr96(α,n)Mo99 cross section for astrophysics and applications

The reaction $^{96}\mathrm{Zr}(\ensuremath{\alpha},\mathrm{n})^{99}\mathrm{Mo}$ plays an important role in $\ensuremath{\nu}$-driven wind nucleosynthesis in core-collapse supernovae and is a possible avenue for medical isotope production. Cross-section measurements were performed using the activation technique at the Edwards Accelerator Laboratory. Results were analyzed along with world data on the $^{96}\mathrm{Zr}(\ensuremath{\alpha},n)$ cross section and $^{96}\mathrm{Zr}(\ensuremath{\alpha},\ensuremath{\alpha})$ differential cross section using large-scale Hauser-Feshbach calculations. We compare our data, previous measurements, and a statistical description of the reaction. We find a larger cross section at low energies compared to prior experimental results, allowing for a larger astrophysical reaction rate. This may impact results of core-collapse supernova $\ensuremath{\nu}$-driven wind nucleosynthesis calculations but does not significantly alter prior conclusions about $^{99}\mathrm{Mo}$ production for medical physics applications. The results from our large-scale Hauser-Feshbach calculations demonstrate that phenomenological optical potentials may yet be adequate to describe $(\ensuremath{\alpha},n)$ reactions of interest for $\ensuremath{\nu}$-driven wind nucleosynthesis, albeit with regionally adjusted model parameters.

Measurement of Galactic 26Al with the Compton Spectrometer and Imager

Abstract The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2–5 MeV sky. COSI’s energy resolution of ∼0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keV γ-ray line from decaying Galactic 26Al. Most 26Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46 day flight on a NASA superpressure balloon. Here, we detail the first search for the 1809 keV 26Al line in the COSI 2016 balloon flight using a maximum-likelihood analysis. We find a Galactic 26Al flux of (8.6 ± 2.5) × 10−4 ph cm−2 s−1 within the Inner Galaxy (∣ℓ∣ ≤ 30°, ∣b∣ ≤ 10°) with 3.7σ significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPectrometer on INTEGRAL (SPI) and the Compton Telescope on the Compton Gamma-Ray Observatory (COMPTEL). This analysis demonstrates COSI’s powerful capabilities for studies of γ-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.

Comparison between Core-collapse Supernova Nucleosynthesis and Meteoric Stardust Grains: Investigating Magnesium, Aluminium, and Chromium

Abstract Isotope variations of nucleosynthetic origin among solar system solid samples are well documented, yet the origin of these variations is still uncertain. The observed variability of 54Cr among materials formed in different regions of the protoplanetary disk has been attributed to variable amounts of presolar, chromium-rich oxide (chromite) grains, which exist within the meteoritic stardust inventory and most likely originated from some type of supernova explosion. To investigate if core-collapse supernovae (CCSNe) could be the site of origin of these grains, we analyze yields of CCSN models of stars with initial masses 15, 20, and 25 M ⊙, and solar metallicity. We present an extensive abundance data set of the Cr, Mg, and Al isotopes as a function of enclosed mass. We find cases in which the explosive C ashes produce a composition in good agreement with the observed 54Cr/52Cr and 53Cr/52Cr ratios as well as the 50Cr/52Cr ratios. Taking into account that the signal at atomic mass 50 could also originate from 50Ti, the ashes of explosive He burning also match the observed ratios. Addition of material from the He ashes (enriched in Al and Cr relative to Mg to simulate the make-up of chromite grains) to the solar system’s composition may reproduce the observed correlation between Mg and Cr anomalies, while material from the C ashes does not present significant Mg anomalies together with Cr isotopic variations. In all cases, nonradiogenic, stable Mg isotope variations dominate over the variations expected from 26Al.

Supernova Nucleosynthesis, Radioactive Nuclear Reactions and Neutrino-Mass Hierarchy

The ν-process nucleosynthesis in core-collapse supernovae is a sensitive probe of unknown neutrino mass hierarchy through the MSW effect. We carefully studied the uncertainties of almost one hundred ν-induced and nuclear reactions associated with the nucleosynthesis and found that the ν-16O and 11C(α,p)14N reactions among them have the biggest effect on the final 7Li/11B isotopic abundance ratio. The neutrino mass hierarchy is constrained in our nucleosynthetic method with measured 7Li/11B value in SiC-X presolar grains. The inverted hierarchy is statistically more favored at the 2-σ C.L. [1].

First direct measurement of Cu59(p,α)Ni56 : A step towards constraining the Ni-Cu cycle in the cosmos

Reactions on the proton-rich nuclides drive the nucleosynthesis in Core-Collapse Supernovae (CCSNe) and in X-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p-nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between $^{59}$Cu(p,$\alpha$)$^{56}$Ni and $^{59}$Cu(p,$\gamma$)$^{60}$Zn, could potentially halt the production of heavier elements. Here, we report the first direct measurement of $^{59}$Cu(p,$\alpha$)$^{56}$Ni using a re-accelerated $^{59}$Cu beam and cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of $^{56}$Ni and the experimental rate has been found to be lower than Hauser-Feshbach-based statistical predictions. New results hint that the $\nu p$-process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements.

The impact of asymmetric neutrino emissions on nucleosynthesis in core-collapse supernovae II – progenitor dependences

ABSTRACT We investigate the impact of asymmetric neutrino emissions on explosive nucleosynthesis in core-collapse supernovae (CCSNe) of progenitors with a mass range of 9.5–25 M⊙. We perform axisymmetric, hydrodynamic simulations of the CCSN explosion with a simplified neutrino transport, in which anticorrelated dipolar emissions of νe and ${\bar{\nu }}_{\rm e}$ are imposed. We then evaluate abundances and masses of the CCSN ejecta in a post-processing manner. We find that the asymmetric ν-emission leads to the abundant ejection of p- and n-rich matter in the high-νe and -${\bar{\nu }}_{\rm e}$ hemispheres, respectively. It substantially affects the abundances of the ejecta for elements heavier than Ni regardless of progenitors, although those elements lighter than Ca are less sensitive. Based on these results, we calculate the initial mass function-averaged abundances of the CCSN ejecta with taking into account the contribution from Type Ia SNe. For $m_{\rm asy} = 10/3{{\ \rm per\ cent}}$ and $10{{\ \rm per\ cent}}$, where masy denotes the asymmetric degree of the dipole components in the neutrino emissions, the averaged abundances for elements lighter than Y are comparable to those of the solar abundances, whereas those of elements heavier than Ge are overproduced in the case with $m_{\rm asy} \ge 30{{\ \rm per\ cent}}$. Our result also suggests that the effect of the asymmetric neutrino emissions is imprinted in the difference of abundance ratio of [Ni/Fe] and [Zn/Fe] between the high-νe and -${\bar{\nu }}_{\rm e}$ hemispheres, indicating that the future spectroscopic X-ray observations of a CCSN remnant will bring evidence of the asymmetric neutrino emissions if exist.

The impact of asymmetric neutrino emissions on nucleosynthesis in core-collapse supernovae

ABSTRACT We investigate the impact of asymmetric neutrino emissions on the explosive nucleosynthesis in neutrino-driven core-collapse supernovae (CCSNe). We find that the asymmetric emissions tend to yield larger amounts of proton-rich ejecta (electron fraction, Ye > 0.51) in the hemisphere of the higher νe emissions, meanwhile neutron-rich matter (Ye < 0.49) are ejected in the opposite hemisphere of the higher ${\bar{\nu }}_{\rm e}$ emissions. For larger asymmetric cases with $\ge 30\, {\rm per\, cent}$, the neutron-rich ejecta is abundantly produced, in which there are too much elements heavier than Zn compared to the solar abundances. This may place an upper limit of the asymmetric neutrino emissions in CCSNe. The characteristic features are also observed in elemental distribution; (1) abundances lighter than Ca are insensitive to the asymmetric neutrino emissions; (2) the production of Zn and Ge is larger in the neutron-rich ejecta even for smaller asymmetric cases with $\le 10\, {\rm per\, cent}$. We discuss these observational consequences, which may account for the (anti)correlations among asymmetries of heavy elements and neutron star kicks in supernova remnants (SNRs). Future SNR observations of the direct measurement for the mass and spatial distributions of α elements, Fe, Zn, and Ge will provide us the information on the asymmetric degree of neutrino emissions.

Explosive nucleosynthesis in core-collapse supernovae and the titanium problem

Based on a new mechanism to drive spherically symmetric core-collapse supernovae, PUSH, we perform full network nucleosynthesis calculations for different progenitors. While the 56–58Ni yields match the observational data very well for certain progenitors, the ejected titanium masses in our calculations are lower than the values inferred from observations. We demonstrate the dependence of ejecta composition on the progenitor structure and the mass cut. Furthermore, we discuss possible solutions to the well-known problem of titanium underproduction.

THEr-PROCESS NUCLEOSYNTHESIS IN THE VARIOUS JET-LIKE EXPLOSIONS OF MAGNETOROTATIONAL CORE-COLLAPSE SUPERNOVAE

The r-process nucleosynthesis in core-collapse supernovae (CC-SNe) is studied, with a focus on the explosion scenario induced by rotation and strong magnetic fields. Nucleosynthesis calculations are conducted based on magneto-hydrodynamical explosion models with a wide range of parameters for initial rotation and magnetic fields. The explosion models are classified in two different types: i.e., prompt-magnetic-jet and delayed-magnetic-jet, for which the magnetic fields of proto-neutron stars (PNSs) during collapse and the core-bounce are strong and comparatively moderate, respectively. Following the hydrodynamical trajectories of each explosion model, we confirmed that r-processes successfully occur in the prompt-magnetic-jets, which produce heavy nuclei including actinides. On the other hand, the r-process in the delayed-magnetic-jet is suppressed, which synthesizes only nuclei up to the second peak ($A \sim 130$). Thus, the r-process in the delayed-magnetic-jets could explain only "weak r-process" patterns observed in metal-poor stars rather than the "main r-process", represented by the solar abundances. Our results imply that core-collapse supernovae are possible astronomical sources of heavy r-process elements if their magnetic fields are strong enough, while weaker magnetic explosions may produce "weak r-process" patterns ($A \lesssim 130$). We show the potential importance and necessity of magneto-rotational supernovae for explaining the galactic chemical evolution, as well as abundances of r-process enhanced metal-poor stars. We also examine the effects of the remaining uncertainties in the nature of PNSs due to weak interactions that determine the final neutron-richness of ejecta. Additionally, we briefly discuss radioactive isotope yields in primary jets (e.g., $^{56}$Ni), with relation to several optical observation of SNe and relevant high-energy astronomical phenomena.

Presolar graphite from the Murchison meteorite: An isotopic study

We studied presolar graphite grains from four density fractions, KE3 (1.65–1.72g/cm3), KFA1 (2.05–2.10g/cm3), KFB1 (2.10–2.15g/cm3), and KFC1 (2.15–2.20g/cm3), extracted from the Murchison (CM2) meteorite, with the ion microprobe. One of the most interesting features of presolar graphite is that isotopic features depend on density. There are grains with 15N and 18O excesses, Si isotopic anomalies, high 26Al/27Al ratios (∼0.1), and Ca and Ti isotopic anomalies, including the initial presence of short-lived 41Ca and 44Ti. These isotopic features are qualitatively explained by nucleosynthesis in core collapse supernovae. We estimate that 76%, 50%, 7% and 1% of the KE3, KFA1, KFB1 and KFC1 grains, respectively, are supernova grains. We performed 3- and 4-zone supernova mixing calculations to reproduce the C, O (18O/16O) and Al isotopic ratios of the KE3 grains, using 15M⊙ model calculations by Rauscher et al. (2002). Isotopic ratios of grains with high 12C/13C ratios (>200) can be reproduced, whereas those of grains with ratios ⩽200 are hard to explain if we assume that graphite grains form in C-rich conditions.We compared the distributions of the 12C/13C ratios of KFB1 and KFC1 grains and their s-process 86Kr/82Kr ratios inferred from bulk noble gas analysis to model calculations of asymptotic giant branch (AGB) stars with a range of mass and metallicity. We conclude that KFB1 grains with 12C/13C⩾100 formed in the outflow of low-mass (1.5, 2 and 3M⊙) low-metallicity (Z=3×10−3 for 1.5, 2 and 3M⊙, Z=6×10−3 for 3M⊙ only) AGB stars and that KFC1 grains with 12C/13C⩾60 formed in those stars as well as in 5M⊙ stars of solar and/or half-solar metallicities. Grains with 12C/13C<20 in all the fractions seem to have multiple origins. Some of them formed in the ejecta of core-collapse supernovae. J stars and born-again AGB stars are also possible stellar sources.We calculated the abundances of graphite grains from supernovae and AGB stars in the Murchison meteorite to be 0.24ppm and 0.44ppm, respectively, whereas those of SiC grains from supernovae and AGB stars are 0.063ppm and 5.6ppm, respectively. In contrast to graphite, AGB stars are a dominant source of SiC grains.Since different mineral types have different residence times in the interstellar medium, their abundances in meteorites may not reflect original yields in stellar sources. Even if graphite grains are more easily destroyed than SiC grains, graphite grains from supernovae are more abundant than SiC grains from supernovae (0.24ppm vs. 0.063ppm), indicating that supernovae are a prolific producer of graphite grains. Graphite grains from AGB stars are less abundant than SiC grains from AGB stars (0.44ppm vs. 5.6ppm). This difference may reflect the difference in their parent stars: graphite grains formed in low-metallicity stars, while SiC grains formed in close-to-solar metallicity stars.

Nuclear weak interactions, supernova nucleosynthesis and neutrino oscillation

We study the nuclear weak response in light-to-heavy mass nuclei and calculate neutrino-nucleus cross sections. We apply these cross sections to the explosive nucleosynthesis in core-collapse supernovae and find that several isotopes of rare elements 7Li, 11B, 138La, 180Ta and several others are predominantly produced by the neutrino-process nucleosynthesis. We discuss how to determine the suitable neutrino spectra of three different flavors and their anti-particles in order to explain the observed solar system abundances of these isotopes, combined with Galactic chemical evolution of the light nuclei and the heavy r-process elements. Light-mass nuclei like 7Li and 11B, which are produced in outer He-layer, are strongly affected by the neutrino flavor oscillation due to the MSW (Mikheyev-Smirnov-Wolfenstein) effect, while heavy-mass nuclei like 138La, 180Ta and r-process elements, which are produced in the inner O-Ne-Mg layer or the atmosphere of proto-neutron star, are likely to be free from the MSW effect. Using such a different nature of the neutrino-process nucleosynthesis, we study the neutrino oscillation effects on their abundances, and propose a new novel method to determine the unknown neutrino oscillation parameters, θ13 and mass hierarchy, simultaneously. There is recent evidence that some SiC X grains from the Murchison meteorite may contain supernova-produced neutrino-process 11B and 7Li encapsulated in the grains. Combining the recent experimental constraints on θ13, we show that although the uncertainties are still large, our method hints at a marginal preference for an inverted neutrino mass hierarchy for the first time.

Asymmetry in the neutrino and anti-neutrino reactions in a nuclear medium

We study the effect of the density-dependent axial and vector form factors on the electron–neutrino (νe) and anti-neutrino (ν¯e) reactions for a nucleon in nuclear matter or in 12C. The nucleon form factors in free space are presumed to be modified for a bound nucleon in a nuclear medium. We adopt the density-dependent form factors calculated by the quark–meson coupling (QMC) model, and apply them to the νe and ν¯e induced reactions with the initial energy E=8–80 MeV. We find that the total νe cross sections on 12C as well as on a nucleon in nuclear matter are reduced by about 5% at the nuclear saturation density, ρ0. This reduction is caused by the modification of the nucleon structure in matter. Although the density effect for both cases is relatively small, it is comparable with the effect of Coulomb distortion on the outgoing lepton in the ν-reaction. In contrast, the density effect on the ν¯e reaction reduces the cross section significantly in both nuclear matter and 12C cases, and the amount maximally becomes of about 35% around ρ0. Such large asymmetry in the νe and ν¯e cross sections, which seems to be nearly independent of the target, is originated from the differences in the helicities of ν¯e and νe. It is expected that the asymmetry influences the r-process and also the neutrino-process nucleosynthesis in core-collapse supernovae.

New open-source approaches to the modeling of stellar collapse and the formation of black holes

We present new approaches to the simulation of stellar collapse, the formation of black holes, and explosive core-collapse supernova nucleosynthesis that build upon open-source codes and microphysics. We discuss the new spherically-symmetric general-relativistic (GR) collapse code GR1D that is endowed with an approximate 1.5D treatment of rotation, comes with multiple nuclear equations of state, and handles neutrinos with a multi-species leakage scheme. Results from a first set of spinning black hole formation simulations are presented. We go on to discuss the derivative code GR1D+N which is tuned for calculations of explosive nucleosynthesis and includes a NSE/non-NSE equation of state treatment, and a nuclear reaction network. We present sample results showing GR1D+N’s performance in reproducing previous results with thermal-bomb-driven explosions. Finally, we introduce the 3 + 1 GR Zelmani core collapse simulation package and present first results obtained in its application to the 3D modeling of failing core-collapse supernovae.

Neutrino mixing and nucleosynthesis in core-collapse supernovae

A simple description of core-collapse supernovae is given. Properties of the neutrino-driven wind, neutrino fluxes and luminosities, reaction rates and the equilibrium electron fraction in supernova environments are discussed. Neutrino mixing and neutrino interactions that are relevant to core-collapse supernovae are briefly reviewed. The values of electron fraction under several evolution scenarios that may impact rapid neutron-capture process (r-process) nucleosynthesis are calculated.

Nuclear Reactions Governing the Nucleosynthesis of44Ti

Large excesses of 44Ca in certain presolar graphite and silicon carbide grains give strong evidence for 44Ti production in supernovae. Furthermore, recent detection of the 44Ti γ line from the Cas A supernova remnant by the Compton Gamma Ray Observatory Compton Telescope shows that radioactive 44Ti is produced in supernovae. These make the 44Ti abundance an observable diagnostic of supernovae. Through use of a nuclear reaction network, we have systematically varied reaction rates and groups of reaction rates to experimentally identify those that govern 44Ti abundance in core-collapse supernova nucleosynthesis. We survey the nuclear-rate dependence by repeated calculations of the identical adiabatic expansion, with peak temperature and density chosen to be 5.5 × 109 K and 107 g cm-3, respectively, to approximate the conditions in detailed supernova models. We find that, for equal total numbers of neutrons and protons (η = 0),44Ti production is most sensitive to the following reaction rates:44Ti(α, p)47V, α(2α, γ)12C,44Ti(α, γ)48Cr, and 45V(p, γ)46Cr. We tabulate the most sensitive reactions in order of their importance to the 44Ti production near the standard values of currently accepted reaction rates, at both a reduced reaction rate (times 0.01) and an increased reaction rate (times 100) relative to their standard values. Although most reactions retain their importance for η > 0, that of 45V(p, γ)46Cr drops rapidly for η ≥ 0.0004. Other reactions assume greater significance at greater neutron excess:12C(α, γ)16O,40Ca(α, γ)44Ti,27Al(α, n)30P,30Si(α, n)33S. Because many of these rates are unknown experimentally, our results suggest the most important targets for future cross section measurements governing the value of this observable abundance.

Neutrino-induced nucleosynthesis in core-collapse supernovae

Almost all of the 3 · 1053 ergs liberated in a core collapse supernova is radiated as neutrinos by the cooling neutron star. These neutrinos can excite nuclei in the mantle of the star by their neutral and charged current reactions. The resulting spallation reactions are an important nucleosynthesis mechanism that may be responsible for the galactic abundances of 7Li, 11B, 19F, 138La, 180Ta and a number of other nuclei.