Jittering-Jets Explosion Mechanism (JJEM)

• JJEM is a hydrodynamic mechanism for core-collapse supernovae that relies on episodic, stochastically oriented jets launched by a nascent neutron star.
• 3D simulations and observations reveal that repeated jet episodes create multipolar ejecta and point-symmetric supernova remnant structures.
• The model explains key phenomena including explosion energetics, nucleosynthesis patterns, and neutron star kicks, offering an alternative to neutrino-driven explosions.

The Jittering-Jets Explosion Mechanism (JJEM) is a hydrodynamic paradigm for core-collapse supernova (CCSN) explosions in which the newly born neutron star (NS) launches multiple episodic, stochastically oriented bipolar jets. Each jet episode is powered by transient angular momentum fluctuations in the accreting material, leading to intermittent accretion disks or belts whose axes jitter rapidly on timescales of tens of milliseconds to tenths of a second. The cumulative energy deposited by these jets unbinds the stellar envelope, produces multipolar ejecta, and leaves characteristic point-symmetric morphologies in the remnants. JJEM now provides a comprehensive, physically motivated framework that directly addresses the explosion energetics, observed morphologies, and nucleosynthetic and dynamical signatures of CCSNe (Soker et al., 2024, Shishkin et al., 26 Jun 2026, Soker, 2023, Soker, 2024).

1. Physical Principles and Theoretical Framework

The fundamental premise of JJEM is that stochastic, time-dependent angular momentum—seeded by pre-collapse convection in the Si/O/Ne shells and amplified by post-bounce hydrodynamic instabilities (notably the spiral SASI)—enables the formation of short-lived accretion disks or thick belts around the proto-NS. Each episode lasts τ_episode ≈ 0.01–0.1 s and launches a bipolar jet pair. The disk's axis randomly changes by tens of degrees between episodes, leading to “jittering” in jet directions (Soker et al., 2024, Soker, 2024, Braudo et al., 12 Jun 2026).

Each jet episode has typical parameters:

• Mass per jet: $M_{jet} \sim 10^{-3} - 10^{-2} \, M_\odot$
• Velocity: $v_{jet} \sim (3-10) \times 10^3$ km/s
• Kinetic energy per episode: $E_{jet} \sim 10^{49} - 10^{50}$ erg

The total number of episodes is $N_{episode} \sim 5 - 30$, summing to a canonical CCSN explosion energy $E_{exp} \sim 10^{51}$ erg. The episodic, misaligned launching naturally imprints multipolar, point-symmetric density and velocity structures in the ejecta (Soker et al., 2024, Braudo et al., 13 Mar 2025).

2. Observational Imprints and Validation

JJEM receives direct empirical support from the point-symmetric morphologies of numerous CCSN remnants:

• Vela SNR: Seven identified pairs of clumps/ears and an S-shaped jet-etched O/Ne/Mg-rich main axis, requiring tens of percent of explosion energy in multiple jet episodes. Angular spacings and energetics match JJEM predictions; neutrino-driven or CSM effects are excluded by the symmetry and heavy-element pattern (Soker et al., 2024).
• SNR 0540-69.3: JWST data reveal nearly 180° point symmetry between clumpy ejecta bubbles, with at least three jet episodes required. Quantitative information-theoretic analysis confirms a best-fit rotation of 189°, and a symmetry center offset from the pulsar confirms natal kick induced by asymmetric jets (Shishkin et al., 26 Jun 2026).
• N63A: Three point-symmetric ear-pairs, with jet–counter-jet asymmetries (jet energy ratios up to 3:1 for a given episode) directly ascribed to the inability of thick, transient disks to fully relax over the launching episode. Magnetic reconnection timescales are similar, preserving face asymmetries (Soker, 2023).
• G11.2-0.3, RCW 89, Puppis A, SN 1987A: Additional remnants displaying multipolar, rings, bars, and blowouts, all robustly reproduced in recent 3D JJEM simulations (Akashi et al., 12 May 2026, Soker, 15 Apr 2025, Bear et al., 2024, Soker, 24 Feb 2026).

These features cannot be produced with neutrino-driven convection or CSM influence, which form stochastic, non-symmetric structures with significantly lower energies per finger or spike (Soker et al., 2024, Soker, 2024).

3. Numerical Modeling and Hydrodynamic Simulation

3D hydrodynamic simulations with the FLASH code implement source terms for sequential jet injection, varying axes, opening angles, energetics, and durations according to physically motivated JJEM prescriptions (Braudo et al., 12 Jun 2026, Akashi et al., 12 May 2026, Akashi et al., 31 Mar 2026, Braudo et al., 13 Mar 2025). Key outcomes:

• Morphology: Multiple inclined jet pairs generate a pronounced multipolar ejecta structure, with rings, bars, nozzles, dense blocks, and blowouts that closely match observed SNR morphologies (e.g., Cygnus Loop, SNR J0450.4-7050, W49B).
• Instabilities: Interaction of jets with ambient core leads to the growth of RT and KH instabilities, producing clumpy filaments and enhancing mixing, but the large-scale point symmetry is set by jet episode axes (Braudo et al., 12 Jun 2026, Braudo et al., 13 Mar 2025).
• Ring and bar genesis: Successive pairs of jets with different opening angles compress ejecta into rings (circum-jet rings), bars, and nozzles. Observed projection effects (e.g., partial rings, bright spots) are robustly recovered as a function of viewing geometry (Akashi et al., 12 May 2026, Akashi et al., 31 Mar 2026).

Simulation energetics and timescales agree with both ejecta mass and velocity distributions inferred from SNRs and with the necessary $E_{exp} \approx 10^{51}$ erg (Braudo et al., 12 Jun 2026).

4. JJEM Across Progenitor Types and the NS-BH Mass Gap

JJEM is established as a universal mechanism for all CCSNe progenitor types:

• Stripped-envelope SNe: One-dimensional MESA modeling reveals that convective shells in all models (12–40 $M_\odot$), regardless of envelope loss, harbor zones with $j > 2\times10^{15}$ cm$^2$ s$^{-1}$ beneath the NS mass coordinate, ensuring the formation of intermittent accretion disks (Wang et al., 2 Oct 2025).
• Electron-capture SNe: Helium-rich convective shells supply sufficient stochastic $v_{jet} \sim (3-10) \times 10^3$0 for jet launching after core collapse, with final NS mass $v_{jet} \sim (3-10) \times 10^3$1 and explosion energies matching ECSN observations (Wang et al., 2024).

The JJEM framework also explains the observed NS–BH mass gap (2.5–5 $v_{jet} \sim (3-10) \times 10^3$2) via the ratio of ordered (from pre-collapse core rotation) to stochastic angular momentum. Only when the ordered component dominates are jets confined to polar regions and fail to remove equatorial infall, producing fallback BHs; this transition is sharp and accounts for the sparsity of intermediate-mass remnants (Soker, 2023).

5. Microphysics: Disk Lifetimes, Magnetic Fields, and Jet Collimation

Each jet-launching accretion disk episode is short-lived, with disk lifetime typically only several times the local Keplerian period, $v_{jet} \sim (3-10) \times 10^3$3 (with $v_{jet} \sim (3-10) \times 10^3$4 s at 20 km). Viscous and magnetic relaxation timescales, $v_{jet} \sim (3-10) \times 10^3$5–0.1 s, are typically comparable to or longer than the disk lifetime, preserving asymmetries and allowing for intrinsically unequal jet–counter-jet energy ratios (Soker, 2023, Soker, 2024).

Magnetic field amplification (“stochastic-ω dynamo”) and rapid reconnection in regions $v_{jet} \sim (3-10) \times 10^3$6 thick ($v_{jet} \sim (3-10) \times 10^3$7 km near the NS) are required for efficient jet launching. Current 3D MHD simulations do not reach sufficient resolution to capture these layers, indicating a key limitation for future numerical work (Soker, 2024).

Opening angles of the jets that imprint observable features in SNRs are inferred as $v_{jet} \sim (3-10) \times 10^3$8–$v_{jet} \sim (3-10) \times 10^3$9 from momentum balance arguments and imaging (“ears” and clumps), and jet velocities are consistently estimated at $E_{jet} \sim 10^{49} - 10^{50}$0 km s$E_{jet} \sim 10^{49} - 10^{50}$1 (Soker, 2024, Braudo et al., 12 Jun 2026).

6. Associated Phenomena: Gravitational Waves, Neutron Star Kicks, and Nucleosynthesis

JJEM predicts a distinctive gravitational wave (GW) signature: the turbulent cocoons inflated by jittering jets produce narrowband GW emission at $E_{jet} \sim 10^{49} - 10^{50}$2–30 Hz with strain amplitudes $E_{jet} \sim 10^{49} - 10^{50}$3 Hz$E_{jet} \sim 10^{49} - 10^{50}$4 for Galactic CCSNe, in contrast to the 100–2000 Hz spectrum of neutrino-driven instabilities (Soker, 2023). GW detection of such a low-frequency, temporally modulated signal would unambiguously identify jet-driven CCSNe.

Natal NS kicks are explained by the “kick-by-early asymmetrical pair” (kick-BEAP) mechanism: if the earliest jet episode is asymmetric, the NS receives a recoil velocity of order hundreds of km s$E_{jet} \sim 10^{49} - 10^{50}$5 aligned opposite the most energetic jet (Bear et al., 2024). Subsequent jet episodes launched from the moving NS further preserve or enhance this alignment.

Point-symmetric, jet-driven regions in the ejecta are correlated with enhanced heavy elements (O, Ne, Mg) and also with asymmetric dust production and clumpy nucleosynthetic yields, as observed in SNRs such as Cassiopeia A and SN 1987A (Soker, 23 Sep 2025, Soker, 24 Feb 2026).

7. Comparative Efficacy and Theoretical Status

JJEM offers solutions to several major shortcomings of the delayed-neutrino mechanism:

• Energetics: Neutrino heating alone fails to produce $E_{jet} \sim 10^{49} - 10^{50}$6 values above $E_{jet} \sim 10^{49} - 10^{50}$7 erg for average-mass NSs, while JJEM naturally delivers $E_{jet} \sim 10^{49} - 10^{50}$8 erg (Soker, 2024).
• Remnant statistics: The lack of observed failed CCSNe is consistent with JJEM, as all massive stars are expected to develop convective seed perturbations leading to jets (Wang et al., 2 Oct 2025, Wang et al., 2024).
• Morphology: Only JJEM, with its stochastic, multipolar jets, can account for the observed global point symmetry, ring/nozzle structures, and multi-axis wind-rose features; neutrino-driven explosions can produce small-scale clumps but not persistent global symmetry (Soker et al., 2024, Shishkin et al., 26 Jun 2026).

Current simulation codes implement jet injection at the inner boundary but do not fully resolve disk formation and feedback self-consistently due to the required resolution and magnetic complexity (Soker, 2024, Soker, 2024). Advanced high-resolution, multidimensional MHD studies are a critical next step.

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This mechanism is now supported both by morphologically distinctive, energy-consistent observations of Galactic and extragalactic SNRs and by state-of-the-art 3D simulations. JJEM is emerging as the primary, and possibly universal, explosion mechanism for core-collapse supernovae (Soker, 2024, Braudo et al., 12 Jun 2026, Soker et al., 2024).