Nigora Turaeva, Boris Oksengendler, Farida Iskandarova
The Coulomb explosion is a process that occurs following the formation of multiple charges during Auger cascades, leading to the destruction of solid-state and molecular structures. For unstable multi-charged ions produced at Auger cascades, the destruction cross-section is directly related to the probability of Coulomb explosion, which depends on characteristic times of ion dissociation and electron neutralization. This study demonstrates that the atomic dissociation time decreases with charge. An expression for the neutralization time was obtained within the model, in which the probability of Coulomb explosion is considered as a competition of two processes, ion dissociation and electron neutralization. By using approximation of the effective mass, it was shown that the neutralization time is a function of the effective mass and the width of the valence band of solid states.
Johanna Garzon, Jorge A. Leon, Soledad Torres
et al.
In this article, we study the explosion time of the solution to autonomous stochastic differential equations driven by the fractional Brownian motion with Hurst parameter $H>1/2$. With the help of the Lamperti transformation, we are able to tackle the case of non-constant diffusion coefficients not covered in the literature. In addition, we provide an adaptive Euler-type numerical scheme for approximating the explosion time.
Mariam Gogilashvili, Jeremiah W. Murphy, Jonah M. Miller
Most massive stars end their lives with core collapse. However, it is not clear which explode as a Core-collapse Supernova (CCSN), leaving behind a neutron star and which collapse to black hole, aborting the explosion. One path to predict explodability without expensive multi-dimensional simulations is to develop analytic explosion conditions. These analytic explosion conditions also provide a deeper understanding of the explosion mechanism and they provide some insight as to why some simulations explode and some do not. The analytic force explosion condition (FEC) reproduces the explosion conditions of spherically symmetric CCSN simulations. In this followup manuscript, we include the dominant multi-dimensional effect that aids explosion, neutrino driven convection, into the FEC. This generalized critical condition (FEC+) is suitable for multi-dimensional simulations and has potential to accurately predict explosion conditions of two- and three-dimensional CCSN simulations. We show that adding neutrino-driven convection reduces the critical condition by $\sim 30\%$, which is consistent with previous multi-dimensional simulations.
From the early radiation of type II-P supernovae (SNe), it has been claimed that the majority of their red supergiant (RSG) progenitors are enshrouded by large amounts of circumstellar material (CSM) at the point of explosion. The inferred density of this CSM is orders of magnitude above that seen around RSGs in the field, and is therefore indicative of a short phase of elevated mass-loss prior to explosion. It is not known over what timescale this material gets there: is it formed over several decades by a `superwind' with mass-loss rate $\dot{M} \sim10^{-3}\,{\rm M_\odot\,yr^{-1}}$; or is it formed in less than a year by a brief `outburst' with $\dot{M}\sim10^{-1}\,{\rm M_\odot\,yr^{-1}}$? In this paper, we simulate spectra for RSGs undergoing such mass-loss events, and demonstrate that in either scenario the CSM suppresses the optical flux by over a factor of 100, and that of the near-IR by a factor of 10. We argue that the `superwind' model can be excluded as it causes the progenitor to be heavily obscured for decades before explosion, and is strongly at odds with observations of II-P progenitors taken within 10 years of core-collapse. Instead, our results favour abrupt outbursts $<$1 year before explosion as the explanation for the early optical radiation of II-P SNe. We therefore predict that RSGs will undergo dramatic photometric variability in the optical and infrared in the weeks-to-months before core-collapse.
Helium star - carbon-oxygen white dwarf (CO WD) binaries are potential single-degenerate progenitor systems of thermonuclear supernovae. Revisiting a set of binary evolution calculations using the stellar evolution code $\texttt{MESA}$, we refine our previous predictions about which systems can lead to a thermonuclear supernova and then characterize the properties of the helium star donor at the time of explosion. We convert these model properties to NUV/optical magnitudes assuming a blackbody spectrum and support this approach using a matched stellar atmosphere model. These models will be valuable to compare with pre-explosion imaging for future supernovae, though we emphasize the observational difficulty of detecting extremely blue companions. The pre-explosion source detected in association with SN 2012Z has been interpreted as a helium star binary containing an initially ultra-massive WD in a multi-day orbit. However, extending our binary models to initial CO WD masses of up to $1.2\,M_{\odot}$, we find that these systems undergo off-center carbon ignitions and thus are not expected to produce thermonuclear supernovae. This tension suggests that, if SN 2012Z is associated with a helium star - WD binary, then the pre-explosion optical light from the system must be significantly modified by the binary environment and/or the WD does not have a carbon-rich interior composition.
Some catastrophic stellar explosions, such as supernovae (SNe), compact binary coalescences, and micro-tidal disruption events, are believed to be embedded in the accretion disks of active galactic nuclei (AGN). We show high-energy neutrinos can be produced efficiently through $pp$-interactions between shock-accelerated cosmic rays and AGN disk materials shortly after the explosion ejecta shock breaks out of the disk. AGN stellar explosions are ideal targets for joint neutrino and electromagnetic (EM) multimessenger observations. Future EM follow-up observations of neutrino bursts can help us search for yet-discovered AGN stellar explosions. We suggest that AGN stellar explosions could potentially be important astrophysical neutrino sources. The contribution from AGN stellar explosions to the observed diffuse neutrino background depends on the uncertain local event rate densities of these events in AGN disks. By considering thermonuclear SNe, core-collaspe SNe, gamma-ray burst associated SNe, kilonovae, and choked GRBs in AGN disks with known theoretical local event rate densities, we show that these events may contribute to $\lesssim10\%$ of the observed diffuse neutrino background.
Type IIP supernovae (SNe IIP), which represent the most common class of core-collapse (CC) SNe, show a rapid increase in continuum polarization just after entering the tail phase. This feature can be explained by a highly asymmetric helium core, which is exposed when the hydrogen envelope becomes transparent. Here we report the case of a SN IIP (SN~2017gmr) that shows an unusually early rise of the polarization, $\gtrsim 30$ days before the start of the tail phase. This implies that SN~2017gmr is an SN IIP that has very extended asphericity. The asymmetries are not confined to the helium core, but reach out to a significant part of the outer hydrogen envelope, hence clearly indicating a marked intrinsic diversity in the aspherical structure of CC explosions. These observations provide new constraints on the explosion mechanism, where viable models must be able to produce such extended deviations from spherical symmetry, and account for the observed geometrical diversity.
John Lee Grenfell, Stefanie Gebauer, Mareike Godolt
et al.
This work presents theoretical studies which combine aspects of combustion and explosion theory with exoplanetary atmospheric science. Super Earths could possess a large amount of molecular hydrogen depending on disk, planetary and stellar properties. Super Earths orbiting pre-main sequence-M-dwarf stars have been suggested to possess large amounts of O2 produced abiotically via water photolysis followed by hydrogen escape . If these two constituents were present simultaneously, such large amounts of H2 and O2 can react via photochemistry to form up to about 10 Earth oceans. In cases where photochemical removal is slow so that O2 can indeed build up abiotically, the atmosphere could reach the combustion explosion limit. Then, H2 and O2 react extremely quickly to form water together with modest amounts of hydrogen peroxide. These processes set constraints for H2 O2 atmospheric compositions in Super Earth atmospheres. Our initial study of the gas-phase oxidation pathways for modest conditions with Earth insolation and about a tenth of a percent of H2 suggests that H2 is oxidized by O2 into H2O mostly via HOx and mixed HOx NOx catalyzed cycles. Regarding other atmospheric species-pairs we find that CO,O2 mixtures could attain explosive combustive levels on mini gas planets for mid range for the C to O ratio in the equilibrium chemistry regime for p more than about 1bar. Regarding CH4,O2 mixtures, a small number of modeled rocky planets assuming Earth like atmospheres orbiting cooler stars could have compositions at or near the explosive combustive level although more work is required to investigate this issue.
Vanesa Avalos-Gaytán, J. A. Almendral, I. Leyva
et al.
Adaptation plays a fundamental role in shaping the structure of a complex network and improving its functional fitting. Even when increasing the level of synchronization in a biological system is considered as the main driving force for adaptation, there is evidence of negative effects induced by excessive synchronization. This indicates that coherence alone can not be enough to explain all the structural features observed in many real-world networks. In this work, we propose an adaptive network model where the dynamical evolution of the node states towards synchronization is coupled with an evolution of the link weights based on an anti-Hebbian adaptive rule, which accounts for the presence of inhibitory effects in the system. We found that the emergent networks spontaneously develop the structural conditions to sustain explosive synchronization. Our results can enlighten the shaping mechanisms at the heart of the structural and dynamical organization of some relevant biological systems, namely brain networks, for which the emergence of explosive synchronization has been observed.
A detection of a core-collapse supernova (CCSN) gravitational-wave (GW) signal with an Advanced LIGO and Virgo detector network may allow us to measure astrophysical parameters of the dying massive star. GWs are emitted from deep inside the core and, as such, they are direct probes of the CCSN explosion mechanism. In this study we show how we can determine the CCSN explosion mechanism from a GW supernova detection using a combination of principal component analysis and Bayesian model selection. We use simulations of GW signals from CCSN exploding via neutrino-driven convection and rapidly-rotating core collapse. Previous studies have shown that the explosion mechanism can be determined using one LIGO detector and simulated Gaussian noise. As real GW detector noise is both non-stationary and non-Gaussian we use real detector noise from a network of detectors with a sensitivity altered to match the advanced detectors design sensitivity. For the first time we carry out a careful selection of the number of principal components to enhance our model selection capabilities. We show that with an advanced detector network we can determine if the CCSN explosion mechanism is neutrino-driven convection for sources in our Galaxy and rapidly-rotating core collapse for sources out to the Large Magellanic Cloud.
Kevin Ebinger, Sanjana Sinha, Carla Fröhlich
et al.
We report on a method, PUSH, for triggering core-collapse supernova (CCSN) explosions of massive stars in spherical symmetry. This method provides a framework to study many important aspects of core collapse supernovae: the effects of the shock passage through the star, explosive supernova nucleosynthesis and the progenitor-remnant connection. Here we give an overview of the method, compare the results to multi-dimensional simulations and investigate the effects of the progenitor and the equation of state on black hole formation.
A. Navas, J. A. Villacorta-Atienza, I. Leyva
et al.
Synchronization of networked oscillators is known to depend fundamentally on the interplay between the dynamics of the graph's units and the microscopic arrangement of the network's structure. For non identical elements, the lack of quantitative tools has hampered so far a systematic study of the mechanisms behind such a collective behavior. We here propose an effective network whose topological properties reflect the interplay between the topology and dynamics of the original network. On that basis, we are able to introduce the "synchronization centrality", a measure which quantifies the role and importance of each network's node in the synchronization process. In particular, we use such a measure to assess the propensity of a graph to synchronize explosively, thus indicating a unified framework for most of the different models proposed so far for such an irreversible transition. Taking advantage of the predicting power of this measure, we furthermore discuss a strategy to induce the explosive behavior in a generic network, by acting only upon a small fraction of its nodes.
We characterise all the quasi-stationary distributions and the Q-process associated with a continuous state branching process that explodes in finite time. We also provide a rescaling for the continuous state branching process conditioned on non-explosion when the branching mechanism is regularly varying at 0.
Stars with initial masses 10 M_{solar} < M_{initial} < 100 M_{solar} fuse progressively heavier elements in their centres, up to inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion -- an iron-core-collapse supernova (SN). In contrast, extremely massive stars (M_{initial} > 140 M_{solar}), if such exist, have oxygen cores which exceed M_{core} = 50 M_{solar}. There, high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs prior to oxygen ignition, and leads to a violent contraction that triggers a catastrophic nuclear explosion. Tremendous energies (>~ 10^{52} erg) are released, completely unbinding the star in a pair-instability SN (PISN), with no compact remnant. Transitional objects with 100 M_{solar} < M_{initial} < 140 M_{solar}, which end up as iron-core-collapse supernovae following violent mass ejections, perhaps due to short instances of the pair instability, may have been identified. However, genuine PISNe, perhaps common in the early Universe, have not been observed to date. Here, we present our discovery of SN 2007bi, a luminous, slowly evolving supernova located within a dwarf galaxy (~1% the size of the Milky Way). We measure the exploding core mass to be likely ~100 M_{solar}, in which case theory unambiguously predicts a PISN outcome. We show that >3 M_{solar} of radioactive 56Ni were synthesized, and that our observations are well fit by PISN models. A PISN explosion in the local Universe indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic limit, perhaps resulting from star formation processes similar to those that created the first stars in the Universe.
A review of the present status of nova modeling is made, with a special emphasis on some specific aspects. What are the main nucleosynthetic products of the explosion and how do they depend on the white dwarf properties (e.g. mass, chemical composition: CO or ONe)? What's the imprint of nova nucleosynthesis on meteoritic presolar grains? How can gamma rays, if observed with present or future instruments onboard satellites, constrain nova models through their nucleosynthesis? What have we learned about the turnoff of classical novae from observation with past and present X-ray observatories? And last but not least, what are the most critical issues concerning nova modeling (e.g. ejected masses, mixing mechanism between core and envelope)?
We present a new mechanism for core-collapse supernova explosions that relies upon acoustic power generated in the inner core as the driver. In our simulation using an 11-solar-mass progenitor, a strong advective-acoustic oscillation a la Foglizzo with a period of ~25-30 milliseconds (ms) arises ~200 ms after bounce. Its growth saturates due to the generation of secondary shocks, and kinks in the resulting shock structure funnel and regulate subsequent accretion onto the inner core. However, this instability is not the primary agent of explosion. Rather, it is the acoustic power generated in the inner turbulent region and most importantly by the excitation and sonic damping of core g-mode oscillations. An l=1 mode with a period of ~3 ms grows to be prominent around ~500 ms after bounce. The accreting protoneutron star is a self-excited oscillator. The associated acoustic power seen in our 11-solar-mass simulation is sufficient to drive the explosion. The angular distribution of the emitted sound is fundamentally aspherical. The sound pulses radiated from the core steepen into shock waves that merge as they propagate into the outer mantle and deposit their energy and momentum with high efficiency. The core oscillation acts like a transducer to convert accretion energy into sound. An advantage of the acoustic mechanism is that acoustic power does not abate until accretion subsides, so that it is available as long as it may be needed to explode the star. [abridged]