Towards an understanding of Type Ia supernovae from a synthesis of theory and observations

Motivated by the fact that calibrated light curves of Type Ia supernovae (SNe Ia) have become a major tool to determine the expansion history of the Universe, considerable attention has been given to, both, observations and models of these events over the past 15 years. Here, we summarize new observational constraints, address recent progress in modeling Type Ia supernovae by means of three-dimensional hydrodynamic simulations, and discuss several of the still open questions. It will be be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparing them with observations and we show how such models can be applied to study the origin of the diversity of SNe Ia.     

超新星研究进展

本文先介绍超新星巡天和分类,简要地论述历史超新星SN 1006一千年,接着讨论核心塌缩超新星物理和具体事例（SN1987A 20年、 SN2006gy、 2008D）及超新星与γ射线暴的联系,文章重点讨论SNIa 和宇宙学,评述了SNIa在宇宙学中的应用和哈勃常数的确定,最后指出超新星研究目前存在的问题。     

Birthrates and delay times of Type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those infe...     

Modeling Type Ia supernova explosions

Despite their astrophysical significance-as a major contributor to cosmic nucleosynthesis and as distance indicators in observational cosmology-Type Ia supernovae lack theoretical explanation. Not only is the explosion mechanism complex due to the interaction of (potentially turbulent) hydrodynamics and nuclear reactions, but even the initial conditions for the explosion are unknown. Various progenitor scenarios have been proposed. After summarizing some general aspects of Type Ia supernova modeling, recent simulations of our group are discussed. With a sequence of modeling starting (in some cases) from the progenitor evolution and following the explosion hydrodynamics and nucleosynthesis we connect to the formation of the observables through radiation transport in the ejecta cloud. This allows us to analyze several models and to compare their outcomes with observations. While pure deflagrations of Chandrasekhar-mass white dwarfs and violent mergers of two white dwarfs lead to peculiar events (that may, however, find their correspondence in the observed sample of SNe Ia), only delayed detonations in Chandrasekhar-mass white dwarfs or sub-Chandrasekhar-mass explosions remain promising candidates for explaining normal Type Ia supernovae.     

The influence of chemical composition on models of Type Ia supernovae

Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events in this capacity, many fundamental questions remain. Contemporary research investigates how properties of the progenitor system that follow from the host galaxy such as composition and age influence the brightness of an event with the goal of better understanding and assessing the intrinsic scatter in the brightness. We provide an overview of these supernovae and proposed progenitor systems, all of which involve one or more compact stars known as white dwarfs. We describe contemporary research investigating how the composition and structure of the progenitor white dwarf systematically influences the explosion outcome assuming the progenitor is a single white dwarf that has gained mass from a companion. We present results illustrating some of these systematic effects from our research.     

Gravitational wave emission from the single-degenerate channel of Type Ia supernovae

The thermonuclear explosion of a C/O white dwarf as a Type Ia supernova (SN Ia) generates a kinetic energy comparable to that released by a massive star during a SN II event. Current observations and theoretical models have established that SNe Ia are asymmetric, and therefore--like SNe II--potential sources of gravitational wave (GW) radiation. We perform the first detailed calculations of the GW emission for a SN Ia of any type within the single-degenerate channel. The gravitationally confined detonation (GCD) mechanism predicts a strongly polarized GW burst in the frequency band around 1 Hz. Third-generation spaceborne GW observatories currently in planning may be able to detect this predicted signal from SNe Ia at distances up to 1 Mpc. If observable, GWs may offer a direct probe into the first few seconds of the SNe Ia detonation.     

Constraints from Type Ia supernovae on the Λ-CDM model in Randers-Finsler space

Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann equation and a new luminosity distance-redshift relation is proposed. A best-fit to the Type Ia supernovae (SNe) observations yields that the Ω_Λ in the Λ-CDM model is suppressed to almost zero. This fact indicates that the astronomical observations on the Type Ia SNe can be described well without invoking any form of dark energy. The best-fit age of the universe is given. It is in agreement with the age of our galaxy.     

Supernovae Ia in 2017: a long time delay from merger/accretion to explosion

I use recent observational and theoretical studies of type Ia supernovae (SNe Ia) to further constrain the viable SN Ia scenarios and to argue that there must be a substantial time delay between the end of the merger of the white dwarf (WD) with a companion or the end of mass accretion on to the WD and its terminal explosion. This merger/accretion to explosion delay (MED) is required to allow the binary system to lead to a more or less spherical explosion and to prevent a pre-explosion ionizing radiation. Considering these recent results and the required MED, I conclude that the core degenerate scenario is somewhat more favorable over the other scenarios, followed by the double degenerate scenario. Although the single degenerate scenario is viable as well, it is less likely to account for common (normal) SN Ia. As all scenarios require substantial MED, the MED has turned from a disadvantage of the core degenerate scenario to a challenge that theory should overcome. I hope that the requirement for a MED will stimulate the discussion of the different SN Ia scenarios and the comparison of the scenarios to each other.     

A possible resolution of tension between Planck and Type Ia supernova observations

There is an apparent tension between cosmological parameters obtained from Planck cosmic microwave background radiation observations and that derived from the observed magnitude-redshift relation for the type Ia supernova(SNe Ia).Here,we show that the tension can be alleviated,if we first calibrate,with the help of the distance-duality relation,the light-curve fitting parameters in the distance estimation in SNe Ia observations with the angular diameter distance data of the galaxy clusters and then re-estimate the distances for the SNe Ia with the corrected fitting parameters.This was used to explore their cosmological implications in the context of the spatially flat cosmology.We find a higher value for the matter density parameter,m,as compared to that from the original SNLS3,which is in agreement with Planck observations at 68.3%confidence.Therefore,the tension between Planck measurements and SNe Ia observations regarding m can be efectively alleviated without invoking new physics or resorting to extensions for the standard concordance model.Moreover,with the absolute magnitude of a fiducial SNe Ia,M,determined first,we obtained a constraint on the Hubble constant with SNLS3 alone,which is also consistent with Planck.     

A Model of Light from Ancient Blue Emissions

A model is presented to explain the luminar distances and associated red-shifts from ancient supernovae. Light frequencies of supernovae type Ia (SNe Ia) vary smoothly with time, decreasing from singularity to present and intergalactic luminar distances are described as linear combinations of Hubble expansion and smaller components from the time-dependent decrease of emission frequencies. When tested with current cosmic matter densities, SNe Ia distances, red-shifts and the Hubble constant the errors between this model and the vacuum energy model favor this new model, though our model suffers from mathematics about zero. An expression between energy and frequency, derived from the model, reducing to the Planck equation for short observation intervals is also discovered and estimated to within 10% using current SNe Ia data. We also propose a relationship for the deceleration of frequency over time, solve at infinity and discover frequency and time will eventually become uncoupled.     

壳模型对13N Gamow-Teller跃迁的研究

最近的研究表明¹³N的beta衰变对于Ia型超新星爆炸前的电子丰度有着重要的影响.本文在壳模型的基础上,首先计算¹³N基态到基态以及基态到不同激发态的Gamow-Teller(GT)跃迁强度,并将其与实验数据进行了比较.在理论计算的GT强度基础上,对不同温度和密度天体环境下¹³N的电子俘获率进行了细致的计算,并重点讨论基态到激发态的GT跃迁对电子俘获率变化的影响.结果表明,考虑基态到激发态的跃迁后,超新星的电子丰度下降,中微子能量损失增大.基态到激发态跃迁对电子俘获率的影响主要由低激发能级贡献. 关键词： Gamow-Teller跃迁 壳模型 电子俘获 激发态     

Supernovae and properties of matter in the densest and most rarefied states

An overview of the relationship between the astrophysics of supernovae and fundamental physics is given. It is shown how astronomical observations of supernovae are used to determine the parameters of matter in the most rarefied states (“dark energy”); it is also revealed that the mechanism of supernovae explosion is related to the properties of matter in the densest states. The distinction between thermonuclear and collapsing supernovae is explained. Some problems that arise in the theory of powerful cosmic explositions—supernovae and gamma-ray bursts—and which require new physics for solving them are indicated.     

Neutron excess number and nucleosynthesis of heavy elements in a type Ia supernova explosion

Type Ia supernovae produce very powerful burst of light, which can be observed to high redshift. This fact is very attractive for cosmological applications. For supernova light curve modeling, it is very important to know the amount of Fe and Ni, formed during the explosion. In this paper, we explore both the chemical composition of the ejected supernova shells and the possibility of weak r-process under increased neutron excess number based on a set of trajectories of tracer particles, calculated in a hydrodynamic model of SNIa explosion. It is shown that no r-process elements are synthesized in the considered supernova model, even for an increased neutron excess number (Y_e ～ 0.4) because of the slow evolution of temperature and density along chosen trajectories. The results of explosive nucleosynthesis are discussed.     

Cosmological constraints from type ia supernovae peculiar velocity measurements

We detect the correlated peculiar velocities of nearby type Ia supernovae (SNe), while highlighting an error in some of the literature. We find sigma8 = 0.79 +/- 0.22 from SNe, and examine the potential of this method to constrain cosmological parameters in the future. We demonstrate that a survey of 300 low-z SNe (such as the nearby SNfactory) will underestimate the errors on w by approximately 35% if the coherent peculiar velocities are not included.     

Problems with small area surveys: lensing covariance of supernova distance measurements

While luminosity distances from type Ia supernovae (SNe) are a powerful probe of cosmology, the accuracy with which these distances can be measured is limited by cosmic magnification due to gravitational lensing by the intervening large-scale structure. Spatial clustering of foreground mass leads to correlated errors in SNe distances. By including the full covariance matrix of SNe, we show that future wide-field surveys will remain largely unaffected by lensing correlations. However, "pencil beam" surveys, and those with narrow (but possibly long) fields of view, can be strongly affected. For a survey with 30 arcmin mean separation between SNe, lensing covariance leads to a approximately 45% increase in the expected errors in dark energy parameters.     

Neutrinos,supernovae, and the origin of the heavy elements

Stars of～8-100 M_⊙end their lives as core-collapse supernovae(SNe). In the process they emit a powerful burst of neutrinos,produce a variety of elements, and leave behind either a neutron star or a black hole. The wide mass range for SN progenitors results in diverse neutrino signals, explosion energies, and nucleosynthesis products. A major mechanism to produce nuclei heavier than iron is rapid neutron capture, or the r process. This process may be connected to SNe in several ways. A brief review is presented on current understanding of neutrino emission, explosion, and nucleosynthesis of SNe.     

A review of direct numerical simulations of astrophysical detonations and their implications

Multi-dimensional direct numerical simulations (DNS) of astrophysical detonations in degenerate matter have revealed that the nuclear burning is typically characterized by cellular structure caused by transverse instabilities in the detonation front. Type Ia supernova modelers often use onedimensional DNS of detonations as inputs or constraints for their whole star simulations.While these one-dimensional studies are useful tools, the true nature of the detonation is multi-dimensional. The multi-dimensional structure of the burning influences the speed, stability, and the composition of the detonation and its burning products, and therefore, could have an impact on the spectra of Type Ia supernovae. Considerable effort has been expended modeling Type Ia supernovae at densities above 1×10⁷ g·cm^-3 where the complexities of turbulent burning dominate the flame propagation. However, most full star models turn the nuclear burning schemes off when the density falls below 1×10⁷ g·cm^-3 and distributed burning begins. The deflagration to detonation transition (DDT) is believed to occur at just these densities and consequently they are the densities important for studying the properties of the subsequent detonation. This work will review the status of DNS studies of detonations and their possible implications for Type Ia supernova models. It will cover the development of Detonation theory from the first simple Chapman–Jouguet (CJ) detonation models to the current models based on the time-dependent, compressible, reactive flow Euler equations of fluid dynamics.     

Exploring the potentiality of future standard candles and standard sirens to detect cosmic opacity

In this work, we explore the potentiality of future gravitational wave (GW) and Type Ia supernovae (SNe Ia) measurements to detect cosmic opacity by comparing the opacity-free luminosity distance (LD) of GW events with the opacity-dependent LD of SNe Ia observations. The GW data are simulated from the future measurements of the ground-based Einstein Telescope (ET) and the space-borne Deci-Herz Interferometer Gravitational wave Observatory (DECIGO). The SNe Ia data are simulated from the observations of the Wide Field Infrared Survey Telescope (WFIRST) that will be collected over the next few decades. A binning method is adopted to match the GW data with the SNe Ia data at the same redshift z with a selection criterion \begin{document}$ |\Delta z|<0.005$\end{document}, and most of the available data from the GW measurements is employed to detect cosmic opacity due to improvements in the distribution of the future SNe Ia observations. Results show that the uncertainties of the constraints on cosmic opacity can be reduced to \begin{document}$ \sigma_{\epsilon}\sim 0.0041$\end{document} and 0.0014 at the \begin{document}$ 1\sigma$\end{document} confidence level (CL) for 1000 data points from the ET and DECIGO measurements, respectively. Compared with the allowable limits of intergalactic opacity obtained from quasar continuum observations, these future astronomical observations can be used to verify the cosmic opacity. In this way, GW and SNe Ia measurements can be used as important and effective tools to detect cosmic opacity in the future.     

Living with lambda

This talk presents a brief overview of recent results pertaining to the cosmological constant ‘A’. I summarize the observational situation focussing on observations of high redshift Type Ia supernovae which suggest A > 0. Observations of small angular anisotropies in the cosmic microwave background complement Type Ia supernovae observations and both CMB and Sn can be combined to place strong constraints on the value of A. The presence of a small A-term increases the age of the universe and slows down the formation of large scale structure. I also review recent theoretical attempts to generate a small A-term at the current epoch and a model independent approach for determining the cosmic equation of state.     

Type Ia supernovae at high z

Type Ia supernovae are very powerful probes for cosmology and clear tracers of the past history of the universe. Two independent high-redshift supernova collaborations (the High-Z Team and the Supernova Cosmology Project) have presented this year evidence that we live in a low-matter density universe whose expansion is being accelerated by the presence of a dominant vacuum energy density. The Supernova Cosmology Project by using the searches performed at various z for cosmological purposes has measured high-z supernova rates as well. Those measurements provide unvaluable information on the cosmic star formation history, on the efficiency in producing supernovae out of stars, and on the involved timescale to explosion. The cosmic background due to supernova emission can also be calculated in agreement with the measured rates.