We analyze the statistical properties of the turbulent velocity field in the deflagration model for Type Ia supernovae. In particular, we consider the question of whether turbulence is isotropic and consistent with the Kolmogorov theory at small length scales. Using numerical data from a high-resolution simulation of a thermonuclear supernova explosion, spectra of the turbulence energy and velocity structure functions are computed. We show that the turbulent velocity field is isotropic at small length scales and follows a scaling law that is consistent with the Kolmogorov theory until most of the nuclear fuel is burned. At length scales greater than a certain characteristic scale, turbulence becomes anisotropic. Here, the radial velocity fluctuations follow the scaling law of the Rayleigh-Taylor instability, whereas the angular component still obeys Kolmogorov scaling. In the late phase of the explosion, this characteristic scale drops below the numerical resolution of the simulation. The analysis confirms that a subgrid-scale model for the unresolved turbulence energy is required for the consistent calculation of the flame speed in deflagration models of Type Ia supernovae, and that the assumption of isotropy on these scales is appropriate.
We present a study of the influence of magnetic field strength and morphology in Type Ia Supernovae and their late-time light curves and spectra. In order to both capture self-consistent magnetic field topologies as well evolve our models to late times, a two stage approach is taken. We study the early deflagration phase (1s) using a variety of magnetic field strengths, and find that the topology of the field is set by the burning, independent of the initial strength. We study late time (~1000 days) light curves and spectra with a variety of magnetic field topologies, and infer magnetic field …
Due to the increasing number of observations Type Ia supernovae are nowadays regarded as a heterogeneous class of objects consisting of several subclasses. One of the largest of these is the class of Type Iax supernovae (SNe Iax) which have been suggested to originate from pure deflagrations in CO Chandrasekhar-mass white dwarfs (WDs). Although a few deflagration studies have been carried out, the full diversity of the class is not captured yet. We therefore present a parameter study of single-spot ignited deflagrations with varying ignition locations, central densities, metallicities and comp…
In the classical picture, electron-capture supernovae and the accretion-induced collapse of oxygen-neon white dwarfs (ONeWDs) undergo an oxygen deflagration phase before gravitational collapse produces a neutron star (NS). These types of core collapse events are postulated to explain several astronomical phenomena. In this work, the deflagration phase is simulated for the first time using multidimensional hydrodynamics, with the aim of gaining new insight into the explosive deaths of $8-10~M_\odot$ stars and ONeWDs that accrete material from a binary companion star. The main aim is to determin…
Filling The Pockets: The Spherical Nature of 3D Deflagration in Thermonuclear Supernovae
Florida State University（佛罗里达州立大学）；KU Leuven（荷语鲁汶大学）；University of Hawai’i at Manoa（夏威夷大学马诺阿分校）；Planetary Science Institute（行星科学研究所）；Hamburger Sternwarte（汉堡天文台）
Growing evidence suggests that Type Iax supernovae might be the result of thermonuclear deflagrations of Chandrasekhar-mass white dwarfs in binary systems. We carry out Monte Carlo radiative transfer simulations and predict spectropolarimetric features originating from the supernova explosion and subsequent ejecta interaction with the companion star. Specifically, we calculate viewing-angle dependent flux and polarisation spectra for a 3D model simulating the deflagration of a Chandrasekhar-mass white dwarf and, for a second model, simulating the ejecta interaction with a main-sequence star. W…
(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 complet…
It has long been recognized that the neutrinos detected from the next core-collapse supernova in the Galaxy have the potential to reveal important information about the dynamics of the explosion and the nucleosynthesis conditions as well as allowing us to probe the properties of the neutrino itself. The neutrinos emitted from thermonuclear - type Ia - supernovae also possess the same potential, although these supernovae are dimmer neutrino sources. For the first time, we calculate the time, energy, line of sight, and neutrino-flavor-dependent features of the neutrino signal expected from a thr…
This article presents the study of the effects of magnetic fields on non-distributed nuclear burning fronts as a possible solution to a fundamental problem for the thermonuclear explosion of a Chandrasekhar mass ($M_{Ch}$) white dwarf (WD), the currently favored scenario for the majority of Type Ia SNe (SNe~Ia). All existing 3D hydrodynamical simulations predict strong global mixing of the burning products due to Rayleigh-Taylor (RT) instabilities, which is in contradiction with observations. As a first step and to study the flame physics we present a set of computational magneto-hydrodynamic …
First-Principles Turbulence-Driven Deflagration-to-Detonation Transition Mechanism for Near-Chandrasekhar Mass White Dwarf Progenitors
University of Massachusetts Dartmouth（麻省大学达特茅斯分校）；University of Connecticut, School of Mechanical, Aerospace, and Manufacturing Engineering（康涅狄格大学机械、航空航天与制造工程学院）；Naval Research Laboratory, Laboratories for Computational Physics & Fluid Dynamics（海军研究实验室计算物理与流体动力学实验室）；University of Maryland, Physical Sciences Complex, Stadium Drive（马里兰大学）；Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理学研究所）
The observed sub-class of "superluminous" Type Ia supernovae lacks a convincing theoretical explanation. If the emission of such objects were powered exclusively by radioactive decay of 56Ni formed in the explosion, a progenitor mass close to or even above the Chandrasekhar limit for a non-rotating white dwarf star would be required. Masses significantly exceeding this limit can be supported by differential rotation. We, therefore, explore explosions and predict observables for various scenarios resulting from differentially rotating carbon-oxygen white dwarfs close to their respective limit o…
Observational signatures of thermonuclear electron-capture supernovae -- Ne II line strengthening and color evolution as traces of the explosion mechanism
Heidelberger Institut für Theoretische Studien（海德堡理论研究所）；Queen’s University Belfast（贝尔法斯特女王大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik（海德堡大学天体物理中心，理论天体物理研究所）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Sapienza Università di Roma, Dipartimento di Fisica（罗马智慧大学，物理系）；Trinity College Dublin, The University of Dublin（都柏林三一学院，都柏林大学）；GSI Helmholtzzentrum für Schwerionenforschung（GSI亥姆霍兹重离子研究中心）
Over the past decades, many explosion scenarios for Type Ia supernovae have been proposed and investigated including various combinations of deflagrations and detonations in white dwarfs of different masses up to the Chandrasekhar mass. One of these is the gravitationally confined detonation model. In this case a weak deflagration burns to the surface, wraps around the bound core, and collides at the antipode. A subsequent detonation is then initiated in the collision area. Since the parameter space for this scenario, that is, varying central densities and ignition geometries, has not been stu…
SNe Iax are proposed as one new sub-class of SNe Ia. SNe Iax have been estimated to account for ~5-30% of the total SN Ia rate, and most SNe Iax have been discovered in late-type galaxies. In addition, observations constrain the progenitor systems of some SN Iax progenitors have ages of <80Myr. Recently, the weak deflagration explosions of Ch-mass CO WDs seem to provide a viable physical scenario for SNe Iax. Here, comparing theoretical predictions from BPS calculations with SN Iax observations, we put constraints on the SD Ch-mass model as a possible Iax progenitor. A long delay times of >3Gy…
We present two-dimensional hydrodynamics simulations of near-Chandrasekhar mass white dwarf (WD) models for Type Ia supernovae (SNe Ia) using the turbulent deflagration model with deflagration-detonation transition (DDT). We perform a parameter survey for 41 models to study the effects of the initial central density (i.e., WD mass), metallicity, flame shape, DDT criteria, and turbulent flame formula for a much wider parameter space than earlier studies. The final isotopic abundances of $^{11}$C to $^{91}$Tc in these simulations are obtained by post-process nucleosynthesis calculations. The sur…
The recently observed diversity of Type Ia supernovae (SNe Ia) has motivated us to conduct the theoretical modeling of SNe Ia for a wide parameter range. In particular, the origin of Type Iax supernovae (SNe Iax) has been obscure. Following our earlier work on the parameter dependence of SN Ia models, we focus on SNe Iax in the present study. For a model of SNe Iax, we adopt the currently leading model of pure turbulent deflagration (PTD) of near-Chandrasekhar mass C+O white dwarfs (WDs). We carry out 2-dimensional hydrodynamical simulations of the propagation of deflagration wave, which leave…
Type Ia supernovae are associated with thermonuclear explosions of white dwarf stars. Combustion processes convert material in nuclear reactions and release the energy required to explode the stars. At the same time, they produce the radioactive species that power radiation and give rise to the formation of the observables. Therefore, the physical mechanism of the combustion processes, as reviewed here, is the key to understand these astrophysical events. Theory establishes two distinct modes of propagation for combustion fronts: subsonic deflagrations and supersonic detonations. Both are assu…
We refine our previously introduced parameterized model for explosive carbon-oxygen fusion during thermonuclear supernovae (SN Ia) by adding corrections to post-processing of recorded Lagrangian fluid element histories to obtain more accurate isotopic yields. Deflagration and detonation products are verified for propagation in a uniform density medium. A new method is introduced for reconstructing the temperature-density history within the artificially thick model deflagration front. We obtain better than 5\% consistency between the electron capture computed by the burning model and yields fro…
Stellar evolution models predict the existence of hybrid white dwarfs (WDs) with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with masses ~1.1 Msun, hybrid WDs in a binary system may easily approach the Chandrasekhar mass (MCh) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-MCh hybrid WD under the assumption that nuclear burning only occurs in carbon-rich material. Performing hydrodynamics simulations of the explosion and detailed nucleosynthesis post-processing calculations, we find that only 0.014 Msu…
We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M$_r$ = -17.27 $\pm$ 0.07, and a ($Δm_{15})_r$ = 0.69 $\pm$ 0.04. Comparing our observations to synthe…
Nucleosynthesis in Two-Dimensional Delayed Detonation Models of Type Ia Supernova Explosions
通过对Ia型超新星（SNe Ia）三种极端情况的二维爆炸模拟，探讨了不同爆炸机制的核合成特征：纯湍流爆燃、初始爆燃近似球形点火后的延迟爆轰和高度非对称爆燃点火后的延迟爆轰.除了这个初始条件，爆燃阶段被视为在一个无参数的方法。当湍流燃烧进入分布燃烧区时，爆震开始。这发生在密度约$10^{7}$ g cm $^{-3}$ -相对较低，相比现有的核合成研究一维球对称模型。这些多维模型中的燃烧不同于一维模型中的燃烧，因为爆轰波既传播到白矮星中心附近的高密度区中的未燃烧物质，又传播到表面附近的低密度区。因此，所得到的产物是不同爆炸燃烧产物的混合物，从低密度的碳燃烧产物到最高密度的完全硅燃烧产物，以及在爆燃阶段合成的电子捕获产物。与爆燃模型相反，延迟爆轰产生一种特征性的层状结构，其产率在很大程度上满足银河系化学演化的约束。在非对称延迟爆轰模型中，填充有电子捕获物质（例如，$^{58}$ Ni，$^{54}$ Fe）在壳内，显示出大的偏移，高于$^{56}$ Ni分布的主体，而由爆炸产生的物质分布得更球形（简化）。
Nowadays the number of models aimed at explaining the Type Ia supernova phenomenon is high and discriminating between them is a must-do. In this work we explore the influence of rotation in the evolution of the nuclear flame which drives the explosion in the so called gravitational confined detonation models. Assuming that the flame starts in a point-like region slightly above the center of the white dwarf (WD) and adding a moderate amount of angular velocity to the star we follow the evolution of the deflagration using a smoothed particle hydrodynamics code. We find that the results are very …
The most commonly accepted progenitor system for Type Iax supernovae (SNe Iax) is the partial deflagration of a near-Chandrasekhar-mass white dwarf (WD) accreting from a non-degenerate helium donor star, leaving a bound remnant following the explosion. In this paper, we investigate whether the WD remant can undergo multiple SNe during the system's lifetime. We use Modules for Experiments in Astrophysics (MESA) to evolve various single-degenerate binaries to determine which could plausibly undergo multiple SNe Iax due to multiple helium accretion phases. We also investigate the possibility for …
Recent Suzaku X-ray spectra of SNR 3C 397 indicate enhanced stable iron-group element abundances of Ni, Mn, Cr, and Fe. Seeking to address key questions about the progenitor and explosion mechanism of 3C 397, we compute nucleosynthetic yields from a suite of multidimensional hydrodynamics models in the near-Chandrasekhar mass, single-degenerate paradigm for supernova Type Ia. Varying the progenitor white dwarf internal structure, composition, ignition, and explosion mechanism, we find the best match to the observed iron-peak elements of 3C 397 are dense (central density $\ge$ 6$\times$10$^{9}$…
Type Iax supernovae (SN Iax), also called SN 2002cx-like supernovae, are the largest class of peculiar white dwarf (thermonuclear) supernovae, with over fifty members known. SN Iax have lower ejecta velocity and lower luminosities, and these parameters span a much wider range, than normal type Ia supernovae (SN Ia). SN Iax are spectroscopically similar to some SN Ia near maximum light, but are unique among all supernovae in their late-time spectra, which never become fully nebular. SN Iax overwhelmingly occur in late-type host galaxies, implying a relatively young population. The SN Iax 2012Z …
The Production of Electron-Capture Elements in Thermonuclear Supernovae: Theory vs. Observations
Florida State University（佛罗里达州立大学）；KU Leuven（荷语鲁汶大学）；University of Hawai’i at Manoa（夏威夷大学马诺阿分校）；Space Telescope Science Institute（太空望远镜科学研究所）；Planetary Science Institute（行星科学研究所）；Hamburger Sternwarte（汉堡天文台）
While the importance of supernova feedback in galaxies is well established, its role on the scale of molecular clouds is still debated. In this work, we focus on the impact of supernovae on individual clouds, using a high-resolution magneto-hydrodynamic simulation of a region of 250 pc where we resolve the formation of individual massive stars. The supernova feedback is implemented with real supernovae that are the natural evolution of the resolved massive stars, so their position and timing are self-consistent. We select a large sample of molecular clouds from the simulation to investigate th…
In order for a double-detonation model to be viable for normal type Ia supernovae, the adverse impact of helium-burning ash on early-time observables has to be avoided, which requires that the helium envelope mass should be at most 0.02 solar mass. Most of the previous studies introduced detonation by artificial hot spots, and therefore the robustness of the spontaneous helium detonation remains uncertain. In the present work, we conduct a self-consistent hydrodynamic study on the spontaneous ignition of the helium envelope in the context of the double-degenerate channel, by applying an ideali…
Nuclear shell burning in the final stages of the lives of massive stars is accompanied by strong turbulent convection. The resulting fluctuations aid supernova explosion by amplifying the non-radial flow in the post-shock region. In this work, we investigate the physical mechanism behind this amplification using a linear perturbation theory. We model the shock wave as a one-dimensional planar discontinuity and consider its interaction with vorticity and entropy perturbations in the upstream flow. We find that, as the perturbations cross the shock, their total turbulent kinetic energy is amplif…
We apply the model of stimulated neutrino transitions to neutrinos traveling through turbulence on a non-constant density profile. We describe a method to predict the location of large amplitude transitions and demonstrate the effectiveness of this method by comparing to numerical calculations using a model supernova (SN) profile. The important wavelength scales of turbulence, both those that stimulate neutrino transformations and those that suppress them, are presented and discussed. We then examine the effects of changing the parameters of the turbulent spectrum, specifically the root-mean-s…
The aim of this work is to identify and explain the necessary conditions required for an energetic explosion of a Chandrasekhar-mass white dwarf. We construct and analyze weakly compressible turbulence models with nuclear burning effects for carbon/oxygen plasma at a density expected for deflagration-to-detonation transition (DDT) to occur. We observe formation of carbon deflagrations and transient carbon detonations at early times. As turbulence becomes increasingly inhomogeneous, sustained carbon detonations are initiated by the Zel'dovich reactivity gradient mechanism. The fuel is suitably …
The nature of the progenitors and explosion mechanism of Type Iax supernovae (SNe Iax) remain a mystery. The single-degenerate (SD) systems that involve the incomplete pure deflagration explosions of near-Chandrasekhar-mass white dwarfs (WDs) have recently been proposed for producing SNe Iax, in which non-degenerate companions are expected to survive from SN explosions. In this work we concentrate on the main-sequence (MS) donor SD progenitor systems. By mapping the computed companion models from three-dimensional hydrodynamical simulations of ejecta-companion interaction into a one-dimensiona…
Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acoustic waves. As the acoustic waves cross the shock, the perturbed shock induces a field of entropy and vorticity waves in the post-shock flow. We find that, even when the upstream flow is assumed to be dominated by sonic perturbations, the shock-generate…
A two-dimensional hydrodynamics code for Type Ia supernovae (SNIa) simulations is presented. The code includes a fifth-order shock-capturing scheme WENO, detailed nuclear reaction network, flame-capturing scheme and sub-grid turbulence. For post-processing we have developed a tracer particle scheme to record the thermodynamical history of the fluid elements. We also present a one-dimensional radiative transfer code for computing observational signals. The code solves the Lagrangian hydrodynamics and moment-integrated radiative transfer equations. A local ionization scheme and composition depen…
