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Simulating the jittering-jets explosion mechanism: circum-jet rings account for observed core-collapse supernova remnant morphologies

This paper presents three-dimensional hydrodynamical simulations demonstrating that the jittering-jets explosion mechanism can generate opposite circum-jet rings, thereby successfully explaining the distinct morphological features observed in core-collapse supernova remnants such as G46.8-0.3 and G11.2-0.3.

Original authors: Muhammad Akashi (Technion, Israel), Noam Soker (Technion, Israel)

Published 2026-04-01

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CC BY 4.0

Original authors: Muhammad Akashi (Technion, Israel), Noam Soker (Technion, Israel)

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: How Stars Explode

Imagine a massive star as a giant, over-pressurized balloon. When it runs out of fuel, it collapses in on itself. For decades, scientists have debated exactly how this collapse turns into a massive explosion (a supernova).

One leading theory is called the Jittering Jets Explosion Mechanism (JJEM). Think of the collapsing star's core as a chaotic dance floor. As it spins and wobbles, it shoots out pairs of high-speed "fire hoses" (jets) of energy in random directions. These jets blast outward, shattering the star and creating the explosion.

The Experiment: Simulating the Blast

The authors, Akashi and Soker, used a supercomputer to simulate this explosion in 3D. They wanted to see what happens when you have two rounds of these "fire hoses" shooting out one after the other.

Round 1 (The Wide Jets): First, they launched two wide, powerful jets. Imagine these like a giant, wide-mouthed garden hose spraying water in a broad cone. These jets smash into the star's core, compressing it into a thick, fast-moving shell of gas (like a snowplow pushing a pile of snow).
Round 2 (The Narrow Jets): A few seconds later, they launched a second pair of jets. These were much thinner and faster, like high-pressure water pistols.

The Surprise: The "Donut" Effect

Here is the magic part. When the thin, fast jets catch up to the thick, slow-moving shell created by the first jets, something cool happens:

The thin jets punch a hole through the center of the thick shell.
Instead of just flying straight through, they push the gas sideways.
This sideways push squeezes the gas into two giant, glowing rings (or donuts) surrounding the jets.

The Analogy: Imagine you are pushing a heavy, thick blanket (the first jet's shell) across a table. Then, someone shoots a fast, thin laser beam (the second jet) through the center of the blanket. The laser doesn't just cut a hole; it pushes the fabric of the blanket out to the sides, creating two raised, circular ridges around the hole. That's what the simulations show happening with gas and energy.

What Does This Look Like from Earth?

The shape of these rings depends on how we are looking at them from Earth (the "viewing angle").

Looking from the Side (High Angle): If we look at the rings from the side, we don't see a full circle. Instead, the rings cross our line of sight at two points. It looks like two bright, glowing spots on opposite sides of the explosion, with faint wisps of gas connecting them.
Looking from an Angle: If we look from a bit higher up, we see the full shape: two bright, elliptical rings facing each other like a pair of eyes or a figure-eight.

Connecting the Dots to Real Stars

The authors compared their computer simulations to real photos of two famous supernova remnants (the debris left behind after a star explodes):

SNR G46.8-0.3: This object looks a bit messy, with a "nose" shape and bright spots. Previous theories suggested it was shaped by crashing into clouds of gas in space. However, the authors argue that the clouds don't fit the evidence. Their simulation of the "two pairs of jets" perfectly recreates the "nose" and the bright spots, suggesting the explosion itself created the shape, not the clouds.
SNR G11.2-0.3: This object has two very distinct, bright rings on its outer edge. The authors' simulation shows that when the narrow jets hit the wide-jet shell, they create rings that look almost identical to what we see in this real star remnant.

Why This Matters

This paper strengthens the idea that the Jittering Jets Explosion Mechanism is the real way massive stars explode.

The Claim: If the "two pairs of jets" theory is correct, it should leave behind specific ring-shaped scars.
The Proof: The computer simulation shows that these rings do form naturally from this process.
The Match: Real stars in the sky (like G11.2-0.3) actually have these exact scars.

In short: The universe is like a cosmic art gallery. The authors figured out the "brushstroke" (two pairs of jittering jets) that creates a specific "painting" (the ring-shaped supernova remnants). By matching their simulation to the real paintings in the sky, they are proving that their theory of how stars explode is likely correct.

1. Problem Statement

The paper addresses the challenge of identifying the primary explosion mechanism for Core-Collapse Supernovae (CCSNe). While the Jittering Jets Explosion Mechanism (JJEM) is a leading candidate, it requires robust observational evidence linking specific hydrodynamical outcomes to observed Supernova Remnant (SNR) morphologies.

The Gap: Previous studies have shown that jets can create point-symmetric structures, but the specific formation of circum-jet rings (rings of dense material surrounding the jet axis) and their appearance at various viewing angles needed further investigation.
The Goal: To determine if the interaction between consecutive pairs of jets (a wide pair followed by a narrow pair) within the JJEM framework can reproduce the specific ring-like morphologies observed in SNRs such as G46.8-0.3 and G11.2-0.3, distinguishing them from features caused by interactions with the ambient interstellar medium (ISM).

2. Methodology

The authors conducted three-dimensional hydrodynamical simulations using the Eulerian Adaptive-Mesh Refinement (AMR) code FLASH v4.8.

Physical Setup:
- Stellar Model: A stripped-envelope (Wolf-Rayet) progenitor model (15 $M_\odot$ ) with a dense inner core and an outer envelope.
- Jet Injection: Two consecutive pairs of conical jets were launched along the same symmetry axis (with one misaligned test case):
  1. First Pair (Wide Jets): Launched at $t=0$ for 0.5 s. Half-opening angle $\alpha = 60^\circ$ , velocity $v = 8 \times 10^4$ km/s, total energy $3 \times 10^{51}$ erg. These compress the core to form a dense, fast-expanding shell.
  2. Second Pair (Narrow Jets): Launched at $t_2$ (typically 3 s, also tested at 1 s and 2 s). Half-opening angles varied (e.g., $10^\circ$ and $5^\circ$ ), velocity $v = 8 \times 10^4$ km/s. These catch up to the dense shell, penetrate it, and push material sideways.
Numerical Simplifications:
- Jets were launched at $7 \times 10^8$ cm rather than the physical $\sim$ 10–100 km to save computational resources.
- Gravity was neglected, justified by the high jet energy accelerating material well above escape velocity.
- Only two pairs of jets were simulated; later pairs expected in JJEM were omitted, focusing the analysis on the outer ejecta.
Analysis Metrics:
- Emission Integral (EI): Calculated as $EI = \int \rho^2 dl$ to simulate observational intensity maps.
- Instability Diagnostics: Used the Rayleigh-Taylor diagnostic ( $f_{RT}$ ) and vorticity ( $\nabla \times \vec{v}$ ) to analyze mixing and turbulence.
- Viewing Angles: Simulations were projected at various inclination angles ( $i$ ) from the jet axis to the line of sight ( $49^\circ$ to $90^\circ$ ).

3. Key Contributions

Mechanism of Ring Formation: The study identifies a specific hydrodynamical pathway for ring formation: Wide jets create a dense shell; narrow jets subsequently penetrate this shell, compressing gas laterally to form circum-jet rings.
Robustness of Morphology: The formation of these rings is shown to be a robust process across a wide parameter space (varying jet energies, opening angles, and launch times), requiring no fine-tuning.
Projection Effects: The paper details how the 3D ring structure projects onto the 2D plane of the sky:
- High Inclination ( $i \gtrsim 60^\circ$ ): Rings appear as two distinct bright zones (where the ring crosses the plane of the sky) connected by fainter filaments.
- Low/Medium Inclination: The rings appear as complete, bright elliptical rims.
Jet-Driven Dynamo (JEDD): The simulations confirm that jet-induced shear and vorticity can efficiently amplify magnetic fields in the interaction regions.

4. Key Results

Simulation Evolution: The narrow jets break out of the dense shell formed by the wide jets, creating "ears" that evolve into nozzles. The material pushed to the sides forms dense, clumpy rings due to Rayleigh-Taylor instabilities.
Comparison with SNR G46.8-0.3:
- The observed "nose" structure (two bright zones with faint filaments between them) and the "pipe" (low-density zone) in G46.8-0.3 are poorly explained by interactions with molecular clouds (lack of X-ray/optical emission, mismatch with magnetic field lines).
- The simulation of interacting jets (Run A) at a $90^\circ$ inclination successfully reproduces the two bright zones and the filamentary structure, suggesting the morphology is jet-driven.
Comparison with SNR G11.2-0.3:
- This SNR exhibits two prominent rings on its outer shell.
- The simulation at an inclination of $\approx 50^\circ$ (matching estimates for G11.2-0.3) reproduces the observed features: rings on the outer shell, an inner faint zone, and an extended bright region on the side of the ring ("ring's side").
- The size of the simulated rings can be matched to observations by adjusting jet energy (lower energy yields smaller rings).
Parameter Sensitivity:
- Launch Time ( $t_2$ ): Rings are more prominent when the second pair of jets interacts with a more developed (denser/narrower) shell ( $t_2 \gtrsim 2$ s).
- Misalignment: Introducing a misalignment between jet pairs (Run M) creates asymmetrical ring sides, consistent with observed irregularities in SNRs.

5. Significance

Support for JJEM: The ability of the simulations to reproduce complex, specific morphologies (rings, bright zones, filaments) in real SNRs without fine-tuning provides strong evidence that the Jittering Jets Explosion Mechanism is the primary driver of CCSNe.
Diagnostic Tool: The paper establishes that the presence of circum-jet rings and their specific projection effects can serve as a diagnostic tool to infer the explosion geometry and the sequence of jet ejections in historical supernovae.
Rejection of Alternative Models: By demonstrating that jet interactions explain features in G46.8-0.3 that ambient cloud interactions cannot, the study challenges models relying solely on ISM interaction to explain SNR morphology.
Future Directions: The results suggest that many CCSNRs with high-quality images likely contain signatures of multiple jet pairs, encouraging further observational searches for these specific ring structures to constrain explosion physics.