Cellular Dynamics of Helium-rich Detonation on sub-Chandrasekhar Mass White Dwarf

summary

The gist

The gist The cellular structure was observed at all the parameter range we explored; the upstream density in the range of 105 - 106g cm−3 and the envelope composition of XHe =0.0 and 0.6-1.0 (with

In short

The study investigated cellular dynamics of helium detonation in white dwarf envelopes using terrestrial cell-based theories to understand initiation and quenching thresholds. Results showed that C/O contamination rapidly reduces cell width, suggesting nickel production delay for C/O-rich compositions. The small cell width poses a challenge for full supernova simulations, highlighting the need for sub-grid modeling.

Key concepts

Cellular Structure: This refers to the physical size and arrangement of cells within a detonation wave. In this study, it was observed across various densities and helium compositions. The structure is driven by shock front instability related to nuclear energy generation, and its size is crucial for determining detonation thresholds.
Cell Width Reduction: The width of the cells decreases significantly when C/O contamination from the white dwarf core material is present. This reduction is accelerated by alpha-capture reactions. This finding implies that in C/O-rich environments, the detonation structure becomes very fine, which complicates modeling.
Sub-grid Modeling: This approach involves incorporating the detailed cellular dynamics found in high-resolution simulations into larger, coarser simulations. It is suggested as a solution to overcome the difficulty of resolving the extremely small cell widths in full supernova models, bridging terrestrial and astrophysical detonation research.

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This episode discusses

The paper

Cellular Dynamics of Helium-rich Detonation on sub-Chandrasekhar Mass White Dwarf · Read on arXiv

Kazuya Iwata, Keiichi Maeda

Department of Mechanical Engineering and Science, Kyoto University · Department of Astronomy, Kyoto University

Most previous efforts for hydrodynamic studies on detonation in the context of Type Ia supernovae did not take into account the scale of the cellular structure for a criterion in initiation, propagation, quenching, and the resolution requirement of detonation, whereas it is quite common to consider cell sizes in the discussion on terrestrial detonation in chemically reactive systems. In our recent study, the terrestrial cell-based theories, which incorporates the cell-size data acquired in 2D simulations of helium detonation in the double-detonation model, were demonstrated to be a powerful diagnostics in reproducing the thresholds in the initiation and quenching provided by previous studies. In the present study, 2D simulation results of the cellular detonation in the base of white-dwarf (WD) envelope are described in detail, in terms of the dynamic wave morphology and chemical abundance structure. The cellular structure is observed at a range of upstream density and envelope composition explored in the present work. C/O contamination by the WD core material reduces the cell width rapidly, as accelerated by the α-capture reaction. It is also indicated that nickel production could be significantly delayed for the C/O-rich composition. The small cell width makes it extremely demanding to resolve the detonation structure in full-star simulations of SNe Ia; this could raise a concern on the robustness of the outcomes of some numerical simulations in terms of the success and failure of detonation. This issue may be overcome by sub-grid modeling that incorporates the cellular dynamics acquired in resolved simulations.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Cellular Dynamics of Helium-rich Detonation on sub-Chandrasekhar Mass White Dwarf".

Jocelyn: The gist The cellular structure was observed at all the parameter range we explored;

Vera: First, who's behind it and why it matters.

Paper summary: Vera: This study focuses on the 2D simulation results of cellular detonation happening in the base of a white dwarf envelope <ref:2412.15580#pg1>. They describe how this structure looks in terms of both the dynamic wave shape and how the chemical elements are distributed.

Jocelyn: They found that this cellular structure shows up across all the parameter ranges they explored, including upstream densities between one hundred five and one hundred six g cm−three and different envelope compositions for helium, specifically XHe = zero point zero and ranging from zero point six to one point zero.

Subrahmanyan: And they mentioned something interesting about the C/O contamination from the white dwarf core material; this contamination rapidly shrinks the cell width because of an alpha-capture reaction, which also suggests that nickel production might be significantly delayed if you have a C/O-rich composition.

Conclusion: Vera: Looking at the whole picture, the paper "Cellular Dynamics of Helium-rich Detonation on sub-Chandrasekhar Mass White Dwarf" is showing us that for these white dwarfs, the size of the cellular structure is usually much smaller than the scale height of that star's envelope.

Jocelyn: Except when it's a pure helium medium, which suggests that the double-detonation model could still be a viable scenario for normal type Ia supernovae if you can get that high contamination from the core material in the envelope.

Subrahmanyan: I think what this means is that if we can delay nickel production for those intermediate helium mass fractions, it might help meet some of the constraints coming from early-time observations of these events.

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