The merger of two white dwarfs (WDs) has for many years not been considered as the favoured model for the progenitor system of type Ia supernovae (SNe Ia). But recent years have seen a change of opinion as a number of studies, both observational and theoretical, have concluded that they should contribute significantly to the observed type Ia supernova rate. In this paper, we study the ignition and propagation of detonation through post-merger remnants and we follow the resulting nucleosynthesis up to the point where a homologous expansion is reached. In our study we cover the entire range of WD masses and compositions. For the emergence of a detonation we study three different setups. The first two are guided by the merger remnants from our earlier simulations (Dan et al. 2014}, while for the third one the ignitions were set by placing hotspots with properties determined by spatially resolved calculations taken from the literature. There are some caveats to our approach which we investigate. We carefully compare the nucleosynthetic yields of successful explosions with SN Ia observations. Only three of our models are consistent with all the imposed constraints and potentially lead to a standard type Ia event. The first one, a $0.45\,M_\odot\ {\rm helium\ (He)} + 0.9 \,M_\odot$ carbon-oxygen (CO) WD system produces a sub-luminous, SN 1991bg-like event while the other two, a $0.45\,M_\odot\ {\rm He} + 1.1\,M_\odot$ oxygen-neon (ONe) WD system and a $1.05+1.05\,M_\odot$ system with two CO WDs, are good candidates for common SNe Ia.
We suggest "tidal double detonation": a new mechanism for a thermonuclear explosion of a white dwarf (WD) induced by a tidal disruption event (TDE). Tidal detonation is also a WD explosion induced by a TDE. In this case, helium (He) and carbon-oxygen (CO) detonation waves incinerate He~WD and CO~WD, respectively. On the other hand, for tidal double detonation, He detonation is first excited in the He shell of a CO~WD, and drives CO detonation in the CO core. We name this mechanism after the double detonation scenario in the context of type Ia supernovae. In this paper, we show tidal double det…
Thermonuclear explosions may arise in binaries in which a CO white dwarf (WD) accretes He from a companion. If the accretion rate allows a sufficiently large mass of He to accumulate prior to ignition of nuclear burning, the He surface layer may detonate, giving rise to an astrophysical transient. Detonation of the He layer generates shock waves that propagate into the underlying CO WD. This might directly ignite a detonation at the edge of the CO WD or compress the core of the WD sufficiently to trigger a CO detonation near the centre. If either ignition mechanism works, the two detonations c…
Some simulations of Type Ia supernovae feature self-consistent thermonuclear detonations. However, these detonations are not meaningful if the simulations are not resolved, so it is important to establish the requirements for achieving a numerically converged detonation. In this study we examine a test detonation problem inspired by collisions of white dwarfs. This test problem demonstrates that achieving a converged thermonuclear ignition requires spatial resolution much finer than 1 km in the burning region. Current computational resource constraints place this stringent resolution requireme…
Context: Superluminous type Ia supernovae (SNe Ia) may be explained by super-Chandrasekhar-mass explosions of rapidly rotating white dwarfs (WDs). In a preceding paper, we showed that the deflagration scenario applied to rapidly rotating WDs generates explosions that cannot explain the majority of SNe Ia. Aims: Rotation of the progenitor star allows super-Chandrasekhar-mass WDs to form that have a shallower density stratification. We use simple estimates of the production of intermediate and iron group elements in pure detonations of rapidly rotating WDs to assess their viability in explaining…
We study the initiation of thermonuclear detonations in tidally disrupted white dwarf stars by intermediate-mass ($10^3 M_\odot$) black holes. The length scales required to resolve the initiation mechanism are not easily reached in three-dimensions, so instead we have devised two-dimensional proxy models which, together with a logarithmic gridding strategy, can adequately capture detonation wave fronts as material undergoes simultaneous compression and stretching from tidal forces. We consider 0.15 and 0.6 solar mass white dwarf stars parameterized by tidal strengths in the range $β=4~\text{to…
We study the exceptionally short (32-41 ms) precursors of two intermediate-duration thermonuclear X-ray bursts observed with RXTE from the neutron stars in 4U 0614+09 and 2S 0918-549. They exhibit photon fluxes that surpass those at the Eddington limit later in the burst by factors of 2.6 to 3.1. We are able to explain both the short duration and the super-Eddington flux by mildly relativistic outflow velocities of 0.1$c$ to 0.3$c$ subsequent to the thermonuclear shell flashes on the neutron stars. These are the highest velocities ever measured from any thermonuclear flash. The precursor rise …
We present theoretical delay times and rates of thermonuclear explosions that are thought to produce Type Ia supernovae, including the double-detonation sub-Chandrasekhar mass model, using the population synthesis binary evolution code StarTrack. If detonations of sub-Chandrasekhar mass carbon-oxygen white dwarfs following a detonation in an accumulated layer of helium on the white dwarf's surface ("double-detonation" models) are able to produce thermonuclear explosions which are characteristically similar to those of SNe Ia, then these sub-Chandrasekhar mass explosions may account for at leas…
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 deflagr…
The paper is concerned with identification of the key mechanisms controlling deflagration-to-detonation transition in stellar medium. The issue of thermal runaway triggered by positive feedback between the advancing flame and the flame-driven precompression is discussed in the framework of a one-dimensional flame-folding model. The paper is an extension of the authors' previous study dealing with the non-stoichiometric fusion, $fuel \to products$, kinetics (Phys.Rev.E, 103(2021)) over physically more relevant, $fuel+fuel \to products$, kinetics. Despite this change the runaway effect endures. …
Type Ia supernovae (SNe Ia) originate from the thermonuclear explosions of carbon-oxygen (C-O) white dwarfs (WDs). The single-degenerate scenario is a well-explored model of SNe Ia where unstable thermonuclear burning initiates in an accreting, Chandrasekhar-mass WD and forms an advancing flame. By several proposed physical processes the rising, burning material triggers a detonation, which subsequently consumes and unbinds the WD. However, if a detonation is not triggered and the deflagration is too weak to unbind the star, a completely different scenario unfolds. We explore the failure of th…
During the early evolution of an AM CVn system, helium is accreted onto the surface of a white dwarf under conditions suitable for unstable thermonuclear ignition. The turbulent motions induced by the convective burning phase in the He envelope become strong enough to influence the propagation of burning fronts and may result in the onset of a detonation. Such an outcome would yield radioactive isotopes and a faint rapidly rising thermonuclear ".Ia" supernova. In this paper, we present hydrodynamic explosion models and observable outcomes of these He shell detonations for a range of initial co…
The structure of a thermonuclear detonation wave can be solved accurately and, thus, may serve as a test bed for studying different approximations that are included in multidimensional hydrodynamical simulations of supernova. We present the structure of thermonuclear detonations for the equal mass fraction of $^{12}$C and $^{16}$O (CO) and for pure $^{4}$He (He) over a wide range of upstream plasma conditions. The lists of isotopes we constructed allow us to determine the detonation speeds, as well as the final states for these detonations, with an uncertainty of the percent level (obtained he…
The nature of type Ia supernovae (SNIa) - thermonuclear explosions of white dwarf stars - is an open question in astrophysics. Virtually all existing theoretical models of normal, bright SNIa require the explosion to produce a detonation in order to consume all of stellar material, but the mechanism for the deflagration-to-detonation transition (DDT) remains unclear. We present a unified theory of turbulence-induced DDT that describes the mechanism and conditions for initiating detonation both in unconfined chemical and thermonuclear explosions. The model is validated using experiments with ch…
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…
Progress in the three-dimensional modeling of supernovae (SN) prompts us to revisit the supernova remnant (SNR) phase. We continue our study of the imprint of a thermonuclear explosion on the SNR it produces, that we started with a delayed-detonation model of a Chandrasekhar-mass white dwarf. Here we compare two different types of explosion models, each with two variants: two delayed detonation models (N100ddt, N5ddt) and two pure deflagration models (N100def, N5def), where the N number parametrizes the ignition. The output of each SN simulation is used as input of a SNR simulation carried on …
We present observations and modeling of SN 2016hnk, a Ca-rich supernova (SN) that is consistent with being the result of a He-shell double-detonation explosion of a C/O white dwarf. We find that SN 2016hnk is intrinsically red relative to typical thermonuclear SNe and has a relatively low peak luminosity ($M_B = -15.4$ mag), setting it apart from low-luminosity Type Ia supernovae (SNe Ia). SN 2016hnk has a fast-rising light curve that is consistent with other Ca-rich transients ($t_r = 15$ d). We determine that SN 2016hnk produced $0.03 \pm 0.01 M_{\odot}$ of ${}^{56}\textrm{Ni}$ and $0.9 \pm …
We study a new mechanism for deflagration to detonation transition in thermonuclear supernovae (SNe Ia), based on the formation of shocks by amplification of sound waves in the steep density gradients of white dwarfs envelopes. Given a large enough jump in density a small pressure and velocity perturbation, produced by the turbulent deflagration, turns into a shock down of the gradient, where it will dissipate and heat up the media. With the right frequency and amplitude the heating can be enough to initiate a detonation, which can propagate backward and up the density gradient. We studied pla…
The detonation of a helium shell on a white dwarf has been proposed as a possible explosion triggering mechanism for Type Ia supernovae. Here, we report ZTF 18aaqeasu (SN 2018byg/ATLAS 18pqq), a peculiar Type I supernova, consistent with being a helium-shell double-detonation. With a rise time of $\approx 18$ days from explosion, the transient reached a peak absolute magnitude of $M_R \approx -18.2$ mag, exhibiting a light curve akin to sub-luminous SN 1991bg-like Type Ia supernovae, albeit with an unusually steep increase in brightness within a week from explosion. Spectra taken near peak lig…
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…
Some binary systems composed of a white dwarf (WD) and a hot subdwarf (sdB) helium star will make contact within the helium burning lifetime of the sdB star. The accreted helium on the WD inevitably undergoes a thermonuclear instability, causing a detonation that is expected to transition into the WD core and lead to a thermonuclear supernova while the donor orbits nearby with high velocity. Motivated by the recent discovery of fast-moving objects that occupy unusual locations on the HR diagram, we explore the impact of the thermonuclear supernovae on the donors in this specific double detonat…
Supernovae of type Ia are thought to arise from the thermonuclear incineration of a carbon-oxygen white dwarf stellar remnant. However, the detailed explosion scenario and stellar evolutionary origin scenario -- or scenarios -- which lead to observed supernovae are still quite uncertain. One of the principal tests of proposed scenarios is comparison with the explosion products inferred, for example, from the spectrum of the supernovae. Making this comparison requires computation of the combustion dynamics and products through simulation of proposed scenarios. Here we discuss two specific propo…
We demonstrate tidal detonation during a tidal disruption event (TDE) of a helium (He) white dwarf (WD) with $0.45M_\odot$ by an intermediate mass black hole (IMBH) by extremely high-resolution simulations. Tanikawa et al. (2017) have showed tidal detonation in previous studies results from unphysical heating due to low-resolution simulations, and such unphysical heating occurs in 3-dimensional (3D) smoothed particle hydrodynamics (SPH) simulations even with $10$ million SPH particles. In order to avoid such unphysical heating, we perform 3D SPH simulations up to $300$ million SPH particles, a…
Thermonuclear supernovae are the result of the violent unbinding of a white dwarf, but the precise nature of the explosion mechanism(s) is a matter of active debate. To this end, several specific scenarios have been proposed to explain the observable traits of SNe Ia. A promising pathway is the double-detonation scenario, where a white dwarf accretes a shell of helium-rich material from a companion and a detonation in the resulting helium shell is the primary cause of the explosion. Through a set of two-dimensional grid-based simulations of this scenario we clearly distinguish three phases of …
Detonation initiation in a reactive medium can be achieved by an externally created shock wave. Supersonic flow onto a gravitating center, known as Bondi-Hoyle-Lyttleton (BHL) accretion, is a natural shock wave creating process, but, to our knowledge, a reactive medium has never been considered in the literature. Here, we conduct an order of magnitude analysis to investigate under which conditions the shock-induced reaction zone recouples to the shock front. We derive three semianalytical criteria for self-sustained detonation ignition. We apply these criteria to the special situation where a …
Using 2D and 3D simulation, we study the "robustness" of the double detonation scenario for Type Ia supernovae, in which a detonation in the helium shell of a carbon-oxygen white dwarf induces a secondary detonation in the underlying core. We find that a helium detonation cannot easily descend into the core unless it commences (artificially) well above the hottest layer calculated for the helium shell in current presupernova models. Compressional waves induced by the sliding helium detonation, however, robustly generate hot spots which trigger a detonation in the core. Our simulations show tha…
Type Ia supernovae (SNe) are believed to be caused by the thermonuclear explosion of a white dwarf (WD), but the nature of the progenitor system(s) is still unclear. Recent theoretical and observational developments have led to renewed interest in double degenerate models, in particular the "helium-ignited violent merger" or "dynamically-driven double-degenerate double-detonation" (D$^6$). In this paper we take the output of an existing D$^6$ SN model and carry it into the supernova remnant (SNR) phase up to 4000 years after the explosion, past the time when all the ejecta have been shocked. A…
Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon-oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recently, Sharon & Kushnir (2022) used The Zwicky Transient Facility Bright Transient Survey to construct a synthesized $^{56}$Ni mass, $M_\text{Ni56}$, distribution of SNe Ia. They found that the rate of low-luminosity ($M_\text{Ni56}\approx0.15\,M_{\odot}$) SNe Ia is lower by a factor of $\sim10$ than the more common $M_\text{Ni56}\approx0.7\,M_{\odot}$ events. We here show that in order for the double-detonation model (DDM, in which a…
Detonations in helium-rich envelopes surrounding white dwarfs have garnered attention as triggers of faint thermonuclear ".Ia" supernovae and double detonation Type Ia supernovae. However, recent studies have found that the minimum size of a hotspot that can lead to a helium detonation is comparable to, or even larger than, the white dwarf's pressure scale height, casting doubt on the successful ignition of helium detonations in these systems. In this paper, we examine the previously neglected effects of C/O pollution and a full nuclear reaction network, and we consider hotspots with spatially…
The progenitor system(s) and the explosion mechanism(s) of Type Ia supernovae (SNe Ia) are still under debate. Non-electromagnetic observables, in particular gravitational waves and neutrino emission, of thermonuclear supernovae are a complementary window to light curves and spectra for studying these enigmatic objects. A leading model for SNe Ia is the thermonuclear incineration of a near-Chandrasekhar mass carbon-oxygen white dwarf star in a "delayed-detonation". We calculate a three-dimensional hydrodynamic explosion for the N100 delayed-detonation model extensively discussed in the literat…
Despite their unique astrophysical relevance, the outcome of white dwarf binary mergers has so far only been studied for a very restricted number of systems. Here we present the results of a survey with more than two hundred simulations systematically scanning the white dwarf binary parameter space. We consider white dwarf masses ranging from 0.2 to 1.2 $M_\odot$ and account for their different chemical compositions. We find excellent agreement with the orbital evolution predicted by mass transfer stability analysis. Much of our effort in this paper is dedicated to determining which binary sys…
Models for supernovae (SNe) arising from thermonuclear explosions of white dwarfs (WDs) have been extensively studied over the last few decades, mostly focusing on the single degenerate (accretion of material of a WD) and double degenerate (WD-WD merger) scenarios. In recent years it was suggested that WD-WD direct collisions provide an additional channel for such explosions. Here we extend the studies of such explosions, and explore the role of Helium-shells in affecting the thermonuclear explosions. We study both the impact of low-mass helium ($\sim0.01$ M$_{\odot})$ shells, as well as high …
Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon-oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recent studies have suggested that a propagating detonation within a thin helium shell surrounding a sub-Chandrasekhar mass CO core can subsequently trigger a detonation within the core (the double-detonation model, DDM). The outcome of this explosion is similar to a central ignition of a sub-Chandrasekhar mass CO WD (SCD). While SCD is consistent with some observational properties of SNe Ia, several computational challenges prohibit a r…
Accreted helium layers on white dwarfs have been highlighted for many decades as a possible site for a detonation triggered by a thermonuclear runaway. In this paper, we find the minimum helium layer thickness that will sustain a steady laterally propagating detonation and show that it depends on the density and composition of the helium layer, specifically C12 and O16. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v_cj=1.5e9 cm/s. Though gravitationally unbound, the ashes still have unburned helium (~ 80% in the thi…
Neutron-star (NS) - white-dwarf (WD) mergers may give rise to observable explosive transients, but have been little explored. We use 2D coupled hydrodynamical-thermonuclear FLASH-code simulations to study the evolution of WD debris-disks formed following WD-disruptions by NSs. We use a 19-elements nuclear-network and a detailed equation-of-state to follow the evolution, complemented by a post-process analysis using a larger 125-isotopes nuclear-network. We consider a wide range of initial conditions and study the dependence of the results on the NS/WD masses ($1.4-2{\rm M_{\odot}}$;$\,{\rm 0.3…
The radiosotope $^{44}$Ti is produced through $α$-rich freezeout and explosive helium burning in type Ia supernovae (SNe Ia). In this paper, we discuss how the detection of $^{44}$Ti, either through late-time light curves of SNe Ia, or directly via gamma rays, can uniquely constrain the origin of SNe Ia. In particular, building upon recent advances in the hydrodynamical simulation of helium-ignited double white dwarf binaries, we demonstrate that the detection of $^{44}$Ti in a nearby SN Ia or in a young galactic supernova remnant (SNR) can discriminate between the double-detonation and double…
We present the results of a systematic numerical study of the onset of mass transfer in double degenerate binary systems and its impact on the subsequent evolution. All investigated systems belong to the regime of direct impact, unstable mass transfer. In all of the investigated cases, even those considered unstable by conventional stability analysis, we find a long-lived mass transfer phase continuing for as many as several dozen orbital periods. This settles a recent debate sparked by a discrepancy between earlier SPH calculations that showed disruptions after a few orbital periods and newer…
Deciphering the explosion mechanism of Type Ia SNe using their remnants II: a deep dive into double detonations with SNR 0509-67.5
University of Virginia（弗吉尼亚大学）；Virginia Institute for Theoretical Astronomy, University of Virginia（弗吉尼亚大学理论天体物理研究所）；Towson University（陶森大学）；The University of New South Wales（新南威尔士大学）；Australian National University（澳大利亚国立大学）；South African Astronomical Observatory（南非天文台）；University of Cape Town（开普敦大学）；National Institute for Theoretical and Computational Sciences（国家理论与计算科学研究所）
Several models for type Ia-like supernovae events rely on the production of a self-sustained detonation powered by nuclear reactions. In the absence of hydrogen, the fuel that powers these detonations typically consists of either pure helium (He) or a mixture of carbon and oxygen (C/O). Studies that systematically determine the conditions required to initiate detonations in C/O material exist, but until now no analogous investigation of He matter has been conducted. We perform one-dimensional reactive hydrodynamical simulations at a variety of initial density and temperature combinations and f…
We explore the effects of the deflagration to detonation transition (DDT) density on the production of Ni-56 in thermonuclear supernova explosions (type Ia supernovae). Within the DDT paradigm, the transition density sets the amount of expansion during the deflagration phase of the explosion and therefore the amount of nuclear statistical equilibrium (NSE) material produced. We employ a theoretical framework for a well-controlled statistical study of two-dimensional simulations of thermonuclear supernovae with randomized initial conditions that can, with a particular choice of transition densi…
Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of carbon-oxygen white dwarfs. Though the uniformity of their light curves makes them powerful cosmological distance indicators, long-standing issues remain regarding their progenitors and explosion mechanisms. Recent detection of the early ultraviolet pulse of a peculiar subluminous SN Ia has been claimed as new evidence for the companion-ejecta interaction through the single-degenerate channel. Here, we report the discovery of a prominent but red optical flash at $\sim$ 0.5 days after the explosion of a SN Ia which shows hybr…
A thermonuclear explosion triggered by a helium-shell detonation on a carbon-oxygen white dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group elements produced during helium-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a sub-luminous peculiar Type I SN consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the $i$-band peak absolute magnitude is derived to be around -17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated…
The absorption feature O I 7773 is an important spectral indicator for type Ia supernovae (SNe~Ia) that can be used to trace the unburned material at outer layers of the exploding white dwarf. In this work, we use a large sample of SNe~Ia to examine this absorption at early phases (i.e., -13 days <t <-7 days), and make comparisons with the absorption features of Si~II 6355 and Ca~II near-infrared (NIR) triplet. We show that for a subgroup of spectroscopically normal SNe with normal photospheric velocities (i.e., v_si < 12,500 km s^{-1} at optical maximum), the line strength of high velocity fe…
Recent observations have shown a remarkable diversity of observational behaviors and explosion mechanisms in thermonuclear supernovae (SNe). An emerging class of peculiar thermonuclear SNe, called Type Iax, show photometric and spectroscopic behaviors distinct from normal Type Ia. Their origin remains highly controversial, but pure turbulent deflagration of white dwarfs (WDs) has been regarded as the leading formation theory. The large population of Type Iax indicates the existence of unidentified Galactic Type Iax supernova remnants (SNRs). We report evidence that SNR Sgr A East in the Galact…
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…
Type Ia supernovae (SNe Ia) have been an important tool for astronomy for quite some time; however, the nature of their progenitors remains somewhat mysterious. Recent theoretical studies indicated the possibility of producing thermonuclear detonations of carbon-oxygen white dwarfs (CO WDs) at masses less than the Chandrasekhar mass through accretion of helium-rich matter, which would, depending on mass accretion rate, mass, and initial temperature of the WD, spectrally resemble either a normal SN Ia or a peculiar one. This study aims to further resolve the state of binary systems comprised of…
In a companion paper, Seitenzahl et al. (2013) presented a set of three-dimensional delayed detonation models for thermonuclear explosions of near-Chandrasekhar mass white dwarfs (WDs). Here, we present multi-dimensional radiative transfer simulations that provide synthetic light curves and spectra for those models. The model sequence explores both changes in the strength of the deflagration phase (controlled by the ignition configuration) and the WD central density. In agreement with previous studies, we find that the strength of the deflagration significantly affects the explosion and the ob…
