🔭 astrophysics

Explodability matters: how realistic neutrino-driven explosions change explosive nucleosynthesis yields

This study demonstrates that using realistic, time-dependent neutrino-driven explosion simulations across diverse progenitors yields more accurate nucleosynthetic results than simplified bomb or piston models, which tend to artificially overproduce Fe-peak elements and misrepresent lighter element abundances due to inaccurate explosion dynamics.

Original authors: Luca Boccioli, Lorenzo Roberti

Published 2026-03-30

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CC BY 4.0

Original authors: Luca Boccioli, Lorenzo Roberti

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

Imagine a massive star as a giant, cosmic pressure cooker. For millions of years, it cooks up heavy elements like carbon, oxygen, and iron in its core, layer by layer, like an onion. Eventually, the star runs out of fuel, the pressure cooker collapses, and it explodes in a spectacular supernova. This explosion is the universe's way of scattering these ingredients across the cosmos, eventually forming new stars, planets, and even us.

For a long time, scientists trying to predict exactly what gets scattered and how much have been using a very rough recipe. They've been like chefs who say, "Okay, let's just blast the whole thing open with a fixed amount of dynamite and see what happens."

This paper, written by astronomers L. Boccioli and L. Roberti, says: "Hold on, that's not how it works."

Here is the breakdown of their discovery, using some everyday analogies:

1. The Problem: The "One-Size-Fits-All" Explosion

In the past, scientists used two simple methods to simulate a supernova explosion:

The "Bomb" Model: Imagine dropping a giant stick of dynamite right in the center of the star and blowing it up.
The "Piston" Model: Imagine a giant mechanical piston pushing the star's layers outward from the inside.

The problem is that these models are like using a sledgehammer to crack a nut. They force the explosion to happen with a specific amount of energy and a specific "cut-off point" (where the explosion stops and the leftover core begins). They assume every star explodes the same way, regardless of how heavy or dense it is.

2. The Solution: The "Neutrino-Driven" Engine

The authors used a much more sophisticated simulation called GR1D+. Instead of a sledgehammer, they simulated the actual engine of a supernova: neutrinos.

Think of neutrinos as tiny, ghostly particles that flood out of the collapsing core. They don't just sit there; they act like a high-pressure steam engine. They heat up the material behind the shockwave, pushing it outward. If the steam is strong enough, the star explodes. If it's too weak, the star collapses into a black hole.

This new method is "self-consistent." It doesn't force the explosion; it lets the star decide if it can explode and how hard it explodes based on its own internal structure.

3. The Big Discovery: "Explodability" Matters

The paper found that how easy it is to blow up a star (which they call "explodability") changes the recipe for the universe.

The Old Way (Bomb/Piston): Because they used a fixed explosion, they artificially created too many heavy elements like Iron, Cobalt, and Nickel. It's like if every chef in the world used the same amount of salt, regardless of the soup they were making. Some soups would be too salty, and others too bland.
The New Way (Neutrino-Driven): They found that lighter stars might not explode at all (they just collapse), while heavier stars might explode with different strengths.
- Result: When they used the realistic model, they found less Iron-peak elements than the old models predicted. The "sledgehammer" models were overcooking the heavy elements.

4. The "Mass Cut" Mystery

Imagine the star is a layered cake. When it explodes, the shockwave travels up through the layers.

The "Mass Cut" is the line where the explosion stops. Everything below that line stays behind (becoming a neutron star or black hole), and everything above gets flung into space.
The Old Models: They drew this line arbitrarily, often to make sure exactly the right amount of a specific radioactive element (Nickel-56) was ejected to match one famous explosion (SN 1987A).
The New Models: The line moves naturally. For some stars, the explosion fizzles out early, leaving a bigger chunk of the cake behind. For others, it blasts through more layers. This changes the mix of elements we see in the universe.

5. Why This Matters to You

You might think, "Who cares about how much Iron a star makes?" But this matters because:

We are made of stardust. The iron in your blood, the calcium in your bones, and the oxygen you breathe were all forged in these explosions.
The "Recipe" was wrong. If the old models said stars produced 20% more Iron than they actually do, then our understanding of how the universe evolved over billions of years is slightly off.
Predicting the Future. By understanding the "neutrino engine" better, we can predict which stars will explode and which will silently collapse into black holes, helping us understand the life cycle of the galaxy.

The Bottom Line

This paper is like upgrading from a toy explosion to a realistic physics simulation.

The authors showed that the old, simple ways of simulating supernovae were "cooking" the universe's ingredients incorrectly, producing too much heavy metal. By using a more realistic engine (neutrinos) and letting the stars explode on their own terms, they found a more accurate recipe for the chemical makeup of our universe.

In short: The universe isn't a factory with a single setting; it's a diverse kitchen where every star has its own unique recipe, and we finally have a better way to read the menu.

1. Problem Statement

Core-collapse supernovae (CCSNe) are the primary source of heavy elements in the universe. However, current predictions of nucleosynthetic yields suffer from significant uncertainties arising from two main sources:

Stellar Evolution: Differences in pre-supernova (pre-SN) progenitor structures generated by different stellar evolution codes (e.g., treatment of convection, rotation, binary interactions).
Explosion Physics: The reliance on simplified, non-physical explosion models (such as "piston" or "bomb" models) in the literature. These models arbitrarily set the explosion energy, mass cut (the boundary between the remnant and ejecta), and explosion dynamics to match specific observational constraints (like SN 1987A), rather than deriving them self-consistently from the physics of the explosion.

This arbitrary approach leads to large errors in predicted yields, particularly for Iron-peak elements and lighter isotopes, and fails to capture the complex relationship between progenitor compactness, explosion energy, and remnant mass.

2. Methodology

The authors conducted a comprehensive study comparing nucleosynthesis yields derived from state-of-the-art neutrino-driven explosions against those from traditional simplified models.

Progenitor Sets: They utilized three distinct sets of pre-SN progenitors from leading stellar evolution codes:
- WH07 (Kepler): 32 single stars (12–120 $M_\odot$ ) at solar metallicity.
- LC18 (Franec): 108 single stars with varying masses, metallicities ($[Fe/H] = 0$ to $-3$), and initial rotation velocities.
- F23 (MESA): 35 single and 31 binary-stripped stars (solar metallicity).
Explosion Simulations:
- Used GR1D+, a spherically symmetric code incorporating general relativity, state-of-the-art neutrino transport (M1 moments scheme), and a time-dependent mixing-length theory (MLT) model for neutrino-driven convection.
- Simulations ran for several seconds post-bounce to allow for self-consistent shock revival and the natural emergence of the mass cut and explosion energy.
- Nuclear Equation of State: SFHo.
Nucleosynthesis Calculations:
- Performed in post-processing using SkyNet with a network of 1500 isotopes.
- Trajectories were extrapolated up to 30 seconds post-bounce.
- Electron fraction ( $Y_e$ ) evolution was tracked self-consistently based on neutrino interactions within the simulation.
Comparative Analysis:
- Results were compared against the original yields from the progenitor papers (WH07, LC18, F23) and other 1D neutrino-driven studies (e.g., Curtis et al. 2019 using the PUSH method).
- Yields were weighted by a Salpeter Initial Mass Function (IMF) to assess the impact on Galactic Chemical Evolution (GCE).

3. Key Contributions

Self-Consistent Explosion Modeling: The paper demonstrates that using a neutrino-driven engine (GR1D+) yields explosion energies and remnant masses that align with observations of Type II-P, IIb, and Ib supernovae, as well as recent 3D simulations.
Systematic Comparison: It provides the first extensive comparison of nucleosynthesis yields across three different stellar evolution codes using a single, sophisticated explosion engine, isolating the effects of stellar structure versus explosion dynamics.
Quantification of Simplified Model Errors: The study quantifies the systematic biases introduced by piston and bomb models, specifically regarding Fe-peak element production and the treatment of "explodability" (which stars explode vs. which collapse to black holes).
Black Hole Supernovae (BHSNe): The authors identify a class of high-compactness progenitors that undergo successful shock revival but subsequently collapse into black holes due to excessive mass accretion, leading to weak explosions and low $^{56}\text{Ni}$ ejection.

4. Key Results

A. Explosion Properties and Explodability

Correlations: A strong correlation exists between progenitor compactness ( $\xi_{2.0}$ ), iron core mass, explosion energy, and the gravitational mass of the resulting cold neutron star.
Explodability Differences: The neutrino-driven model predicts different explodability outcomes compared to previous 1D studies (e.g., Curtis et al. 2019, Ertl et al. 2016). Specifically, the GR1D+ model predicts that some low-mass stars ( $\sim12-15 M_\odot$ ) may fail to explode, while some intermediate-mass stars ( $\sim25-40 M_\odot$ ) that failed in other models do explode.
BHSNe: Several high-compactness progenitors ( $\xi_{2.0} > 0.5$ ) successfully revive the shock but form black holes shortly after, resulting in significantly lower $^{56}\text{Ni}$ yields than standard models predict.

B. Impact on Nucleosynthesis Yields

Fe-Peak Elements (Fe, Co, Ni, Cu, Zn):
- Overestimation in Simple Models: Piston and bomb models systematically overestimate Fe-peak yields. This is because they often use fixed, high explosion energies (e.g., 1.4–2.5 B) and arbitrary mass cuts that force the ejection of material that would otherwise fall back or remain in the remnant in realistic simulations.
- Temperature Dependence: The simplified models often have shallower temperature gradients, allowing larger regions of the star to undergo incomplete silicon burning, producing more Co, Ni, and Zn.
Light Elements (C, O, Ne, Mg, Si, S):
- Explodability Dominance: The yields of lighter elements are primarily driven by explodability. If a star fails to explode, its light elements are not ejected (only stellar winds contribute).
- Binary vs. Single: The study highlights that binary-stripped stars have different explodability thresholds, significantly altering the relative contribution of Oxygen and light elements to the ISM compared to single-star populations.
Radioactive Isotopes:
- $^{44}\text{Ti}$ and $^{56}\text{Ni}$ : The production of $^{44}\text{Ti}$ is highly sensitive to peak temperatures. The study notes that the choice of the Nuclear Statistical Equilibrium (NSE) threshold temperature in post-processing can artificially enhance $^{44}\text{Ti}$ yields if neutrino interactions are not properly accounted for.
- $Y_e$ Evolution: The self-consistent tracking of $Y_e$ (electron fraction) via neutrino transport leads to different nucleosynthesis outcomes compared to models that assume a fixed $Y_e \approx 0.5$ or use simplified neutrino treatments.

C. Comparison with Previous Works

vs. WH07 (Piston): The authors' yields show better agreement with light elements when WH07 yields are re-weighted by the new explodability criteria. However, Fe-peak elements remain overproduced in WH07 due to the fixed 1.4 B explosion energy.
vs. LC18 (Bomb): LC18 yields are heavily skewed by the fixed ejection of $0.07 M_\odot$ of $^{56}\text{Ni}$ . This forces a large mass cut and high explosion energy, leading to excessive production of Co, Ni, and Zn, and underproduction of Ti, V, Cr, and Mn compared to the neutrino-driven results.
vs. F23 (Bomb): Similar to LC18, the fixed 1 B explosion energy in F23 leads to an overproduction of Fe-peak elements. The study shows that F23's assumption that all stars explode (or fail based on Ertl criteria) significantly alters the ISM enrichment of Oxygen and light elements compared to the GR1D+ explodability.

5. Significance

This paper establishes that explodability and explosion dynamics are critical, non-negligible factors in Galactic Chemical Evolution models.

Correction of Systematic Biases: It demonstrates that the widespread use of piston and bomb models introduces systematic errors, particularly an overproduction of Iron-peak elements.
Validation of 1D+ Models: The results validate that 1D+ simulations with advanced neutrino transport can reproduce trends seen in expensive 3D simulations, making them a viable and necessary tool for generating large yield tables for population studies.
Future Directions: The authors emphasize the need to incorporate realistic explodability criteria and self-consistent explosion dynamics into chemical evolution models to accurately interpret stellar abundances and supernova remnants. They also highlight the importance of pre-SN events (like C-O shell mergers) and multi-dimensional effects (like neutrino-driven winds) for specific isotopes, which remain areas for future investigation.