Periodic Reporting for period 4 - SNeX (The origins of thermonuclear supernova explosions)
Berichtszeitraum: 2025-02-01 bis 2025-07-31
Supernovae (SNe) are the universe's most energetic explosions, playing a vital role in galaxy evolution and building up the universe's chemical composition. Type Ia SNe, arising from the thermonuclear explosion of white dwarfs (WDs) (either through accretion or merger), are crucial as "standard candles" for accurate cosmic distance measurement; they were used to discover the universe's accelerated expansion. Despite their importance, the exact origins of Type Ia SNe remain debated. Furthermore, large SN surveys have revealed a wide variety of non-standard, peculiar SNe sub-types. Although these lack the standardizability of normal Ia's, their estimated rates are comparable, and they are important for chemical evolution. Their unique properties open new questions that likely hold clues to the origins of all thermonuclear SNe. In this ERC project, we explored all types of thermonuclear explosions of WDs producing both "normal" and peculiar SNe, developing novel explosion models to explain their origin and relate them directly to observations. We used extensive simulations to explore a large phase space of initial conditions (including hybrid WDs and the role of Helium) and formation channels, such as Neutron Star–White Dwarf (NS–WD) mergers. Simulation results were followed using radiative transfer codes to provide detailed predictions for observable properties (light-curve, spectra, chemical composition). We also explored expected rates and host environments to link our theoretical models to observed peculiar SNe families.
Understanding the origin of such SNe is a crucial part of our understanding of the evolution of the universe, the origin of the elements, and essentially trying to answer key issues about the universe at large.
Understanding the origin of such SNe is a crucial part of our understanding of the evolution of the universe, the origin of the elements, and essentially trying to answer key issues about the universe at large.
The SNEX project successfully delivered an integrated, observation-facing theoretical framework for modeling thermonuclear supernovae (SNe) and fast transients. This framework simultaneously addressed the three primary progenitor channels—double-degenerate (DD; WD–WD) mergers, single-degenerate (SD; accretion-grown WDs), and neutron-star–white-dwarf (NS–WD) systems—by combining advanced 2D/3D hydrodynamics (AREPO, FLASH, SPH) with tracer-based nucleosynthesis and radiative transfer (LTE and non-LTE). All modeling priorities were rigorously guided by population synthesis (BPS) data, rates, and DTDs.
Core Scientific Results
- DD Channel Revolutionized: We provided the first consistent full model for the origin of Calcium-rich Supernovae (Ca-rich SNe). Focused 3D simulations of comparable-mass WD mergers led to the discovery of novel thermonuclear explosions and new channels for producing hyper-velocity White Dwarfs (WDs). This established a unified model for faint, fast transients and the origin of hyper-runaway WDs (results published in Nature Astronomy). We also finalized models for a new type of peculiar sub-luminous explosion where only the helium shell detonates.
- SD Channel Re-Framed:
- Iax Origin: First-principles 3D deflagration models using FLASH suggested that Type Iax SNe are the most likely outcome from the single-degenerate channel.
- Realistic Double-Detonation: We produced the most realistic initial conditions for the SD channel by mapping WDs evolving through long-term quiescent helium accretion into 3D FLASH simulations. These time-evolved structures robustly yielded normal-Ia observables with testable early-time spectral/UV signatures.
- Dynamics and Rates: The project extended its scope to include the neglected role of triple stellar systems and dynamics in dense stellar environments (clusters) as SN progenitors. This resulted in new analytical methods and the first ever hydrodynamical simulations of common envelopes in triple systems. These results establish the environmental priors necessary for realistic cluster-specific BPS forecasts.
- NS-WD and BH-WD Mergers: We provided detailed 2D models of NS-WD and BH-WD disruptions leading to thermonuclear explosions and producing various faint transients, predicted to be identified by upcoming deep surveys like the Rubin (LSST) survey.
The project successfully acquired and expanded a dedicated HPC facility to over ∼2100 CPU cores and built a cross-disciplinary team. Results were widely disseminated through 28 publications in major astronomy journals (including Nature Astronomy), as well as numerous conference presentations, press releases, public lectures, popular science coverage, and radio interviews.
Core Scientific Results
- DD Channel Revolutionized: We provided the first consistent full model for the origin of Calcium-rich Supernovae (Ca-rich SNe). Focused 3D simulations of comparable-mass WD mergers led to the discovery of novel thermonuclear explosions and new channels for producing hyper-velocity White Dwarfs (WDs). This established a unified model for faint, fast transients and the origin of hyper-runaway WDs (results published in Nature Astronomy). We also finalized models for a new type of peculiar sub-luminous explosion where only the helium shell detonates.
- SD Channel Re-Framed:
- Iax Origin: First-principles 3D deflagration models using FLASH suggested that Type Iax SNe are the most likely outcome from the single-degenerate channel.
- Realistic Double-Detonation: We produced the most realistic initial conditions for the SD channel by mapping WDs evolving through long-term quiescent helium accretion into 3D FLASH simulations. These time-evolved structures robustly yielded normal-Ia observables with testable early-time spectral/UV signatures.
- Dynamics and Rates: The project extended its scope to include the neglected role of triple stellar systems and dynamics in dense stellar environments (clusters) as SN progenitors. This resulted in new analytical methods and the first ever hydrodynamical simulations of common envelopes in triple systems. These results establish the environmental priors necessary for realistic cluster-specific BPS forecasts.
- NS-WD and BH-WD Mergers: We provided detailed 2D models of NS-WD and BH-WD disruptions leading to thermonuclear explosions and producing various faint transients, predicted to be identified by upcoming deep surveys like the Rubin (LSST) survey.
The project successfully acquired and expanded a dedicated HPC facility to over ∼2100 CPU cores and built a cross-disciplinary team. Results were widely disseminated through 28 publications in major astronomy journals (including Nature Astronomy), as well as numerous conference presentations, press releases, public lectures, popular science coverage, and radio interviews.
The SNEX project fundamentally advanced the state of the art by delivering a fully integrated, multi-channel 3D theoretical framework guided by progenitor demographics, significantly moving beyond previous fragmented studies.
Progress Highlights:
- DD Merger Cartography: We created a unified, phase-connected view of DD mergers, linking explosion outcomes (faint/fast transients) to stellar remnants (hyper-runaway WDs). This provided the first consistent explanation for Ca-rich SNe.
- Physically Seeded SD Models: We developed the first 3D sub-Chandrasekhar models using time-evolved, quiescent He-accretion structures, resolving a major weakness found in previous modeling that relied on simplified ad hoc shells.
- SD Channel Clarified: The framework successfully reframed the SD channel's primary observable outcome as Type Iax SNe through first-principles 3D deflagration, addressing a decades-old theoretical tension.
- NS/BH-WD Mergers: Our detailed 2D models of NS-WD and BH-WD disruptions leading to thermonuclear explosions provided predictions for various faint transients observable by upcoming deep surveys.
- Environment-Aware Progenitors: The project pioneered the integration of advanced three-body/cluster dynamics into the progenitor modeling pipeline, providing the essential environmental priors required to make population synthesis for cluster-based SNe realistic.
The remaining outputs expected from the final work phase are:
- Publication of four (under review) papers detailing the new peculiar sub-luminous explosions from low-mass hybrid WD mergers; Iax SNe from the SD channel; 3D models of peculiar SNe from very low-mass WDs with large helium shells.
Progress Highlights:
- DD Merger Cartography: We created a unified, phase-connected view of DD mergers, linking explosion outcomes (faint/fast transients) to stellar remnants (hyper-runaway WDs). This provided the first consistent explanation for Ca-rich SNe.
- Physically Seeded SD Models: We developed the first 3D sub-Chandrasekhar models using time-evolved, quiescent He-accretion structures, resolving a major weakness found in previous modeling that relied on simplified ad hoc shells.
- SD Channel Clarified: The framework successfully reframed the SD channel's primary observable outcome as Type Iax SNe through first-principles 3D deflagration, addressing a decades-old theoretical tension.
- NS/BH-WD Mergers: Our detailed 2D models of NS-WD and BH-WD disruptions leading to thermonuclear explosions provided predictions for various faint transients observable by upcoming deep surveys.
- Environment-Aware Progenitors: The project pioneered the integration of advanced three-body/cluster dynamics into the progenitor modeling pipeline, providing the essential environmental priors required to make population synthesis for cluster-based SNe realistic.
The remaining outputs expected from the final work phase are:
- Publication of four (under review) papers detailing the new peculiar sub-luminous explosions from low-mass hybrid WD mergers; Iax SNe from the SD channel; 3D models of peculiar SNe from very low-mass WDs with large helium shells.