arXiv subjects

Amir Michaelis

Publications and source records attributed to Amir Michaelis.

9 recordsLinked to original sources

arXiv2026

Simulating observed point-symmetric core-collapse supernova morphologies with the jittering jets explosion mechanism

We conduct two three-dimensional hydrodynamic simulations of the jittering-jets explosion mechanism (JJEM) of core-collapse supernova (CCSN), launching three pairs of inclined opposite jets into the core of an enveloped-stripped stellar model, and reproduce some morphological features of observed CCSN remnants (CCSNRs) that a single pair of jets or instabilities alone cannot reproduce. We launch the three pairs of jets within about a second, and follow the ejecta for more than 10 seconds until after shock breakout. Our main findings are: (1) Although the jets are choked deep inside the star, they manage to form a pronounced multipolar (point-symmetric) morphology. (2) Instabilities and vortices resulting from the jet-star interaction form small clumps and narrow filaments, some of which form point-symmetric morphology, resembling some observed CCSNRs. (3) The most energetic jet of one simulation forms a large low-density blowout ahead of the ejecta, with filaments dragging behind it, resembling the blowout of the Cygnus Loop. (4) The inner ejecta presents two symmetry axes along two of the three jet axes: one of a pair of rings and one of a pair of nozzles, resembling the structure of the point-symmetric SNR J0450.4-7050. (5) The three pairs of jets compress two dense blocks between their axes. The blocks exhibit a Doppler-shift bipolar outflow highly inclined to the morphological axes along the jet axes. The inclined Doppler-bipolar outflow and morphology axis resembles the CCSNRe W49B and SNR G292.0+1.8. Our study supports the claim that the JJEM is the primary explosion mechanism of CCSNe.

astro-ph.HE↗

arXiv2026

Quantifying Symmetry: Transformation Information for Planetary Nebulae and Supernova Remnants

We present a quantitative symmetry-identification pipeline for astrophysical images based on Transformation Information (TI), an information measure of self-similarity under geometric transformations. TI is expressed as a Kullback-Leibler (cross-entropy) divergence between an image and its rotated or reflected counterpart on the overlapping domain. By scanning rotation angles and reflection axes, we obtain TI curves whose local minima identify symmetry operations. We validate the method on a wind-rose pattern and then apply it to planetary nebulae, where the recovered axes trace bipolar and multipolar lobes consistent with morphology-based classifications. Applying TI to supernova remnants yields estimate axes associated with protrusions, rims, and substructure. To emphasize global morphology, we introduce a thresholded two-level variant that compares binary silhouettes and can reveal outline-driven symmetries. Finally, we quantify symmetry using a minima prominence-to-width score and show that this compact descriptor separates Type Ia and core-collapse remnants into distinct populations for an X-ray sample. TI provides a non-parametric, reproducible framework for symmetry identification, classification and population studies.

astro-ph.IM↗

arXiv2025

It's always the quiet ones: Single Degenerate Double Detonation Type Ia Supernova from Quiescent Helium Accretion

We investigate a sub-Chandrasekhar mass double detonation pathway for Type Ia supernovae arising from single degenerate helium accreting carbon-oxygen white dwarfs. Building on our previous one dimensional study of recurrent helium novae (Hillman et al. 2025), we evolve a 0.7 solar mass white dwarf through steady accretion at 10^-8 Msun yr^-1 until it reaches 1.1 solar mass, yielding realistic, time evolved helium rich profiles. These profiles are mapped into FLASH simulations, incorporating nuclear burning for helium and carbon-oxygen detonation, in multi-dimensional hydrodynamic runs. A localized, modest temperature perturbation near the base of the helium shell robustly triggers an outward helium-shell detonation. The ensuing inward propagating shock converges in the carbon-oxygen core, igniting a secondary detonation that unbinds the star. We obtain a Ni56 yield of ~0.64 solar mass, an intermediate-mass element (Si-Ca) mass of ~0.41 solar mass, and maximum ejecta velocities approaching 22,000 km/s, values consistent with normal Type Ia supernovae. Our results demonstrate that recurrent helium accretors, typically quiescent over long timescales, can evolve under subtle, "quiet" conditions to trigger robust double detonations, supporting their role as viable progenitors of sub-Chandrasekhar mass Type Ia supernovae.

astro-ph.HE↗

arXiv2025

The Single-Degenerate Channel Leads to Type Iax and Not Type Ia Supernovae due to Premature Ignition

Type Ia supernovae (SNe Ia) are a critical tool for cosmology and galactic enrichment, yet the progenitor systems of normal SNe Ia remain a central puzzle. The long-debated single-degenerate (SD) channel, where a white dwarf (WD) accretes mass from a companion, faces major observational conflicts. Here, we present 3D hydrodynamic simulations that resolve these tensions by showing a fundamental dichotomy: accreting WDs predominantly ignite prematurely at sub-Chandrasekhar masses, producing low-energy, incomplete explosions consistent with Type Iax supernovae. Only WDs reaching a narrow mass threshold of 1.37 solar mass undergo complete destruction, characteristic of normal SNe Ia. This "safety valve" mechanism effectively recasts the SD channel as the main pathway to SNe Iax, not normal SNe Ia, providing a unified explanation for the observed scarcity of progenitor signatures in the latter and suggesting alternative channels dominate normal SNe Ia production.

astro-ph.SR↗

arXiv2025

Helium Accumulation and Thermonuclear Instabilities on Accreting White Dwarfs: From Recurring Helium Novae to Type Ia Supernovae

We investigate helium accumulation on carbon-oxygen (CO) white dwarfs (WDs), exploring a broad parameter space of initial WD masses ($0.65$--$1.0M_{\odot}$) and helium accretion rates ($10^{-10}$--$10^{-4}M_{\odot}\text{yr}^{-1}$). Our simulations, which were allowed to run for up to the order of a Gyr, reveal distinct regimes determined by the given accretion rate: at higher rates ($\gtrsim10^{-5}M_\odot\rm yr^{-1}$), the mass is repelled by radiation pressure without accretion; intermediate rates ($\sim10^{-8}$--$10^{-5}M_{\odot}\text{yr}^{-1}$) produce periodically recurring helium nova eruptions, enabling gradual WD mass growth; and lower rates ($\lesssim 10^{-8}M_{\odot}\text{yr}^{-1}$) facilitate prolonged, uninterrupted helium accumulation, eventually triggering a thermonuclear runaway (TNR) which for some cases is at sub-Chandrasekhar masses, indicative of a type Ia supernova (SNe) ignition, i.e. providing a potential single-degenerate channel for sub-Chandra SNe. Our models indicate that the WD mass and the helium accumulation rate critically determine the ignition mass and TNR energetics. We identify compositional and thermal signatures characteristic of each regime, highlighting observational diagnostics relevant to helium-rich transients. We discuss these theoretical results in the context of the observed helium nova V445 Puppis, emphasizing helium accretion's pivotal role in shaping diverse thermonuclear phenomena.

astro-ph.SR↗

arXiv2025

Simulating the shaping of point-symmetric structures in the jittering jets explosion mechanism

We conduct three-dimensional hydrodynamical simulations of core-collapse supernovae by launching several pairs of jets into a collapsing core model and show that the jittering jets explosion mechanism (JJEM) can form a point-symmetric morphology that accounts for observed morphologies of about a dozen core-collapse supernovae (CCSN) remnants. Point-symmetric morphologies are composed of pairs of opposite structures around the center of the CCSN remnant. In the JJEM, the newly born neutron star launches several to a few tens of pairs of jets with stochastically varying directions, and these jets explode the star. In the simulations with the FLASH numerical code, we launch pairs of jets with varying directions, energies, opening angles, and durations into the massive stellar core and follow their evolution for about two seconds. We show that the jets form pairs of opposite filaments, clumps, bubbles, and lobes, namely, prominent point-symmetric morphologies. The interaction of the jets with the core leads to vigorous Rayleigh-Taylor instabilities and excites many vortices, which also shape clumps and filaments. Our results suggest that the JJEM could play a central role in the explosion mechanism of CCSNe; neutrino heating can boost the role of jets.

astro-ph.HE↗

arXiv2022

Rapid decline in the lightcurves of luminous supernovae by jet-driven bipolar explosions

We calculate the lightcurves of jet-driven bipolar core collapse supernova (CCSN) explosions into a bipolar circumstellar mater (CSM) and show that an equatorial observer finds the lightcurves to possess a rapid, and even an abrupt, drop. The scenario that might lead to such an explosion morphology is a common envelope evolution (CEE) where shortly before the CCSN explosion the RSG progenitor interacts with a more compact companion that spirals-in and spins-up the core. The companion can be a main sequence star, a neutron star, or a black hole. The binary interaction ejects a shell through an intensive wind and the CEE ejects a denser gas in the equatorial plane. We assume that the companion accretes mass and launches jets. We conduct three-dimensional (3D) hydrodynamical simulations where we launch weak jets, the shaping jets, into the dense shell and show that the interaction forms a bipolar CSM. As a result of the rapid pre-collapse core rotation jets drive the CCSN explosion. We simulate the interaction of the jets with the bipolar CSM and use a simple scheme to calculate the lightcurves. We show that the abrupt drop in the lightcurve of an observer not too close to the polar directions can account for the lightcurve of the hydrogen poor luminous supernova (LSN) SN 2018don. Our study strengthens the claim that jet-driven explosions account for many, even most, CCSNe.

astro-ph.HE↗

arXiv2022

The Grand Canonical Multiverse and the Small Cosmological Constant

We consider the Multiverse as an ensemble of universes. Using standard statistical physics analysis we get that the Cosmological Constant (CC) is exponentially small. The small and finite CC is achieved without any anthropic reasoning. We then quantize the CC. The quantization allows a precise summation of the possible contributions and using the measured value of the CC yields a prediction on the temperature of the Multiverse that we define. Furthermore, quantization allows the interpretation of a single Universe as a superposition of different eigenstates with different energy levels rather than the existence of an actual Multiverse.

hep-th↗

arXiv2022

Accretion in massive colliding wind binaries and the effect of wind momentum ratio

We carry out a numerical experiment of ejecting winds in a massive colliding wind binary system, and quantifying the accretion onto the secondary star under different primary mass loss rates. We set a binary system comprising a Luminous Blue Variable (LBV) as the primary and a Wolf-Rayet (WR) star as the secondary, and vary the mass loss rate of the LBV to obtain different values of wind momentum ratio $η$. Our simulations include two sets of cases: one where the stars are stationary, and one that includes the orbital motion. As $η$ decreases the colliding wind structure moves closer to the secondary. We find that for $η\lesssim 0.05$ the accretion threshold is reached and clumps which originate by instabilities are accreted onto the secondary. For each value of $η$ we calculate the mass accretion rate and identify different regions in the $\dot{M}_{\rm acc}$ - $η$ diagram. For $0.001 \lesssim η\lesssim 0.05$ the accretion is sub- Bondi-Hoyle-Lyttleton (BHL) and the average accretion rate satisfies the power-law $\dot{M}_{\rm acc} \propto η^{-1.73}$ for static stars. The accretion is not continuous but rather changes from sporadic to a larger duty cycle as $η$ decreases. For $η\lesssim0.001$ the accretion becomes continuous in time and the accretion rate is BHL, up to a factor of 0.4--0.8. The simulations that include the orbital motion give qualitatively similar results, with the steeper power law $\dot{M}_{\rm acc} \propto η^{-1.86}$ for the sub-BHL region and lower $η$ as an accretion threshold.

astro-ph.SR↗