Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae

arXiv:2605.16504 · astro-ph.HE, astro-ph.SR, hep-ph · Submitted 2026-05-15 · Read on arXiv

Listen

Transcript

Introduction to the show: ident: Astrophysics Radio.

Vera: Next we'll be talking about the paper "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae".

Jocelyn: The paper was written by Mariam Gogilashvili and Irene Tamborra from University of Copenhagen.

Vera: Stay tuned as we take you through the paper and discuss its implications.

Title: Vera: Welcome back to the show. Today we're looking at a paper that's been making waves in the astrophysics community, and it has a bit of a mouthful for a title: "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae." Jocelyn, I think this is one of those papers where the title really does tell you exactly what's going on, but let's unpack it for our listeners.

Jocelyn: Absolutely, Vera. So when a massive star runs out of fuel, its core collapses, and whether it explodes as a supernova or just collapses straight into a black hole depends on neutrinos. These are nearly massless particles that are produced in huge numbers during the collapse. And the key thing this paper investigates is something called neutrino flavor conversion — basically, neutrinos can change from one type, or flavor, to another as they're streaming out of the collapsing core.

Vera: And that matters because not all neutrino flavors are equally good at driving the explosion. The electron neutrinos and antineutrinos are the ones that deposit energy behind the shock wave and help push it outward. If some of those convert into other flavors before they get to the shock, the energy deposition changes. And this paper, by Mariam Gogilashvili and Irene Tamborra at the Niels Bohr Institute, simulates what that does to the fate of the star.

Jocelyn: Right. They took one hundred ninety-five different progenitor stars, with masses ranging from nine up to one hundred twenty times the mass of the Sun, and ran simulations of the collapse with and without this flavor conversion included. And the results are pretty dramatic. Without flavor conversion, about twenty-five point six percent of their models fail to explode. But when they turn on flavor conversion, that fraction jumps up significantly — depending on how deep in the star they trigger the conversion, it goes from about fifty-one percent all the way up to ninety-six percent.

Vera: So essentially, neutrinos changing flavor can turn a would-be supernova into a quiet collapse into a black hole. And that's a huge shift in our understanding of what happens to massive stars at the end of their lives. Now, one thing I want to emphasize is that this is a schematic treatment — they're not simulating the full quantum mechanics of neutrino oscillations, but they're using a parametric model that captures the essential effect. And the fact that even this simplified approach has such a big impact suggests the real thing could be just as important.

Jocelyn: And that's the hook for our next segment, because the implications go beyond just individual stars — this could actually help solve some long-standing puzzles about the rates of supernovae we observe in the universe.

Paper discussion segment 2: Vera: So we've established that "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae" shows that flavor conversion makes failed explosions much more common. But why should we care about the rate of failed supernovae in the first place? Jocelyn, what's the observational situation?

Jocelyn: Well, Vera, there are actually a couple of known problems in the field. The first is called the red supergiant problem. When astronomers look at the progenitors of Type IIP supernovae — these are explosions from red supergiant stars — they notice that there are very few progenitors with masses between about sixteen and thirty solar masses. But stellar evolution theory says there should be plenty of stars in that range. So either those stars are exploding in a way we're not seeing, or they're not exploding at all.

Vera: And this paper suggests that flavor conversion could be exactly what's suppressing those explosions. In their simulations, the sixteen to thirty solar mass range is particularly sensitive to flavor conversion — many of those stars that would have exploded without flavor conversion end up failing when it's included. That would explain why we don't see them as supernovae: they're quietly collapsing into black holes instead.

Jocelyn: Exactly. And there's also the supernova rate problem. The observed cosmic rate of core-collapse supernovae is systematically lower than what we'd expect from the rate of star formation. If a significant fraction of massive stars are failing to explode, that discrepancy starts to make sense. The paper even calculates this using the Salpeter initial mass function, which weights the importance of different stellar masses. Without flavor conversion, about twenty-seven percent of collapses fail. With flavor conversion at the lowest threshold they consider, that jumps to about forty-eight percent.

Vera: Now, I should note that the paper is careful here — they're not claiming this definitively solves these problems. The fraction of failed explosions they get for the more aggressive flavor conversion scenarios, like seventy-four or eighty-eight percent, would actually be too high compared to observational constraints. So it's not that more flavor conversion is always better. It's that the right amount of flavor conversion could naturally explain why we see fewer supernovae than we expect.

Jocelyn: And that's a really important nuance. The observational constraints on failed supernovae — from surveys that look for disappearing stars, and from the diffuse supernova neutrino background — suggest that somewhere between five and fifty percent of collapses fail. So the no-flavor-conversion case at twenty-seven percent is actually consistent with that range. But the flavor conversion cases push it higher, and the question is whether the real physics lands in the sweet spot.

Vera: So the next question is: what does this mean for the actual objects that are left behind? Because if flavor conversion changes which stars explode and which don't, it should also change the masses of the neutron stars and black holes that form. And that's exactly what we're going to dig into next.

Paper discussion segment 3: Vera: We're back with "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae," and we've talked about how flavor conversion increases the rate of failed explosions. But the paper also looks at something more subtle: the masses of the compact remnants that are left behind. Jocelyn, what did they find there?

Jocelyn: This is where things get really interesting, Vera. For the stars that do successfully explode, the presence of flavor conversion actually leads to less massive neutron stars. In their simulations, the baryonic mass of the remnant — that's the mass before you account for the gravitational binding energy — ends up lower when flavor conversion is included. And the reason is that flavor conversion, when it happens at the right place, can actually help revive the shock earlier.

Vera: That seems counterintuitive at first, because we just said flavor conversion makes explosions fail more often. But the paper distinguishes between different scenarios. When flavor conversion happens deep in the star, near the neutrinosphere, it tends to suppress the explosion. But when it happens closer to the stalled shock, it can actually enhance the neutrino heating and trigger the explosion sooner. And an earlier explosion means less time for the proto-neutron star to accrete matter, so it ends up less massive.

Jocelyn: Right. And the numbers bear this out. Without flavor conversion, the baryonic masses of the remnants from successful explosions span a range up to about one point nine solar masses. With flavor conversion, they tend to cluster lower, around one point two to one point four solar masses after you account for the gravitational mass correction. And that's actually a big deal, because the observed neutron star mass distribution peaks right around one point two to one point four solar masses.

Vera: So the standard simulations without flavor conversion tend to produce neutron stars that are too heavy compared to what we actually observe. And this paper shows that flavor conversion naturally brings the theoretical predictions into better agreement with the observed low-mass tail of the neutron star population. That's a really elegant result — it's not just about the rate of explosions, but about the properties of the objects that survive.

Jocelyn: For the failed explosions, the effect is a bit different. The remnant masses tend to be slightly larger when flavor conversion is included, because the shock never revives and accretion continues for longer. But the paper notes that these masses shouldn't be interpreted as the final black hole masses, because there could be significant fallback of the stellar envelope later on.

Vera: So the picture that emerges is that flavor conversion isn't just a detail — it's a fundamental ingredient that shapes both which stars explode and what they leave behind. And this has implications for gravitational wave observations, for the neutron star mass distribution, and for our understanding of how black holes form. But I should also mention that the authors are careful to note the limitations of their approach. They're using a schematic treatment of flavor conversion, and the results are sensitive to things like the nuclear equation of state and the details of the progenitor models.

Jocelyn: And that's the perfect setup for our final segment, where we'll wrap up what this means for the field and what questions remain open.

Conclusion: Vera: So let's bring it all together. "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae" has shown us that the humble neutrino, changing flavor as it streams out of a collapsing star, can dramatically alter the fate of that star. More failed explosions, especially in that problematic sixteen to thirty solar mass range, and lighter neutron stars when explosions do happen.

Jocelyn: And the implications ripple outward. This could help explain the red supergiant problem, the supernova rate problem, and the fact that observed neutron stars tend to be lighter than many simulations predict. It's a reminder that the microphysics of neutrinos — particles that barely interact with anything — can have macroscopic consequences for the populations of neutron stars and black holes across the universe.

Vera: Of course, the authors are the first to admit that this is a schematic treatment. The real physics of neutrino flavor conversion is enormously complex, involving quantum mechanical effects that are still not fully understood. But papers like this are crucial because they show us what's at stake — they tell us that getting the neutrino physics right isn't just an academic exercise, it's essential for interpreting observations from gravitational wave detectors, X-ray telescopes, and neutrino observatories.

Jocelyn: And that's the takeaway for today. This paper identifies a key missing ingredient in our models of stellar death, and it gives us a roadmap for what needs to be done next — embedding more realistic treatments of flavor conversion into full three-dimensional simulations of core collapse.

Vera: Well said. So we'll be watching for those follow-up papers. For now, we've said goodbye to "Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae" — thanks to Gogilashvili and Tamborra for this thought-provoking work. Join us next time when we'll be looking at a new paper on a completely different corner of the cosmos. Until then, keep looking up.

Jocelyn: And keep asking questions. The universe is full of surprises, and the neutrinos are always up to something. See you next time.

Niels Bohr International Academy and DARK, Niels Bohr Institute, University of Copenhagen · University of Copenhagen

astro-ph.HE, astro-ph.SR, hep-ph

Submitted: 2026-05-15

Updated: 2026-08-18

Comments: 8 pages, 2 figures, 1 table

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 91/100

The gist: * The study addresses a major unsolved problem in astrophysics: determining which massive stars undergo core-collapse supernovae (CCSN) leading to neutron stars, and which fail to explode, leading to

Key concepts

Neutrino flavor conversion: Neutrinos can change between types (flavors) as they travel. In core-collapse supernovae, this affects which neutrinos deposit energy behind the shock wave, influencing whether the star explodes or collapses into a black hole.
Failed core-collapse supernova: When a massive star's core collapses but the shock wave is not revived, the star collapses directly into a black hole instead of exploding. This is called a failed supernova.
Red supergiant problem: Observations show fewer Type IIP supernova progenitors in the 16–30 solar mass range than stellar evolution predicts. The paper suggests that flavor conversion causes many of these stars to fail to explode, explaining the discrepancy.
Baryonic mass: The total mass of a neutron star before accounting for gravitational binding energy. The paper finds that flavor conversion leads to lower baryonic masses for successful explosions, matching observed neutron star masses around 1.2–1.4 solar masses.

Terminology

Core — 45× in this paper · explained in 2 episodes
Metallicity — 4× in this paper · explained in 3 episodes
Adam — 1× in this paper · explained in 2 episodes
Alignment — 1× in this paper · explained in 1 episode
Conservation Laws — 1× in this paper · explained in 3 episodes
Decoupling — 1× in this paper · explained in 2 episodes
Initial Mass Function (IMF) — 1× in this paper · explained in 2 episodes
Modeling Flavor Conversion — 1× in this paper
Multi-messenger Astronomy — 1× in this paper · explained in 3 episodes
Stellar Feedback — 1× in this paper · explained in 2 episodes
Supernova Turbulence in Reduceddimensionality — 1× in this paper
alpha — 1× in this paper · explained in 1 episode

Summary

The study addresses a major unsolved problem in astrophysics: determining which massive stars undergo core-collapse supernovae (CCSN) leading to neutron stars, and which fail to explode, leading to black holes. This uncertainty has direct implications for the birth rates and mass distributions of compact remnants. While initial beliefs suggested black hole formation was limited to progenitors exceeding 40 M, recent spherically symmetric simulations have shown that the CCSN explodability is non-monotonic with the progenitor mass, and black holes can originate from CCSN progenitors with mass as low as 13 M.

Observational evidence of failed explosions suggests that about 5–50% of all collapses fail to produce a visible explosion. These failures are hypothesized to contribute to addressing two key astrophysical issues: the red supergiant problem (the absence of red supergiant progenitors in the mass range 16–30 M) and the CCSN rate problem (the observed cosmic CCSN rate falling below the rate inferred from the cosmic star formation rate).

The core-collapse supernova mechanism is driven by neutrinos, which carry away about 99% of the gravitational binding energy. However, neutrino physics in these events is not fully understood. The paper notes that state-of-art multi-dimensional hydrodynamic simulations of CCSNe do not account for the fact that neutrinos can change their flavor while propagating in the CCSN core. While early on, it was assumed FC (flavor conversion) would have a negligible effect, recent insights question this, showing that FC can take place even in the surroundings of the proto-neutron star.

The authors simulated 195 progenitors with solar metallicity ranging in mass from 9 M to 120 M. The simulation methodology is detailed as follows:

Hydrodynamics: The stellar collapse was modeled using the open-source, spherically symmetric code GR1D, which couples general-relativistic hydrodynamics with energy-dependent neutrino transport.
Resolution: A radial grid of 850 zones was used, resolving the innermost 20 km with uniform spacing and increasing logarithmically at larger radii.
Physics: Neutrino transport utilized an energy-dependent moment formalism (M1 closure) for three species (nu e, e, and nu x). To account for turbulence, the Supernova Turbulence in Reduced dimensionality (STIR) model was employed, with a dimensionless parameter alpha MLT = 1.51.
Modeling Flavor Conversion (FC): FC was implemented using a parametric scheme that instantaneously leads to flavor equipartition while conserving electron lepton number and neutrino momentum for each energy bin. This scheme was applied shortly after bounce (t = 0.02 s) in regions where the matter density is below a threshold baryon density rho c, varied between 10 13 and 10 9 g/cm cubed, spanning the radial region between the neutrinosphere and the stalled shock.

The results demonstrate that FC significantly impacts the probability of a successful explosion.

Overall Trend: Our results suggest that FC increases the fraction of failed explosions, especially in the 16–30 M mass range.
Impact of rho c: The data shows a strong correlation between the depth of flavor equilibration and suppression of shock revival. The fraction of failed collapses increases with increasing rho c. Hence, the deeper inside the proto-neutron star flavor equilibration is achieved, the greater the suppression of shock revival.
Quantitative Results (Table I): The failure rates vary dramatically based on rho c:
In the absence of FC (No FC), f fail is 25.6% at rho c = 109 g/cm3 and 93.3% at rho c = 1013 g/cm3. The IMF-weighted fraction is 27.0%.
When FC is applied, the failure rates increase substantially: For rho c = 109 g/cm3, the IMF-weighted fraction of failed explosions rises to 47.6%. For rho c = 1013 g/cm3, it reaches 88.3%.
Tension with Observations: The authors note that for rho c = 1011 and 10 13 g/cm cubed, the IMF-weighted fractions of failed collapses are 73.9% and 88.3%, seemingly in tension with observational constraints.

FC also influences the baryonic mass (M f) of the resulting compact remnant (Figure 2).

Successful Explosions: For successful CCSNe, FC leads to remnants more compact than those obtained when FC is not taken into account. This results in systematically lower M f values (1.2–1.9 M), which agree better with the bulk of the observed neutron star population, easing the tension regarding the low-mass end of the distribution.
Failed Explosions: For failed explosions, M f tends to be larger in the presence of FC because the absence of shock revival allows for accretion onto the proto-neutron star to continue up to t = 1 s post-bounce. This effect is most pronounced when FC is triggered at higher rho c.

The study concludes that FC has a profound impact on the CCSN explodability and that, overall, FC tends to reduce the net energy deposition behind the stalled shock, systematically favoring failed explosions. The models with mass in the 16–30 M range are particularly sensitive to FC. The authors suggest that The changes induced by FC in this mass range may help alleviate the red supergiant problem [27, 28] as well as the supernova rate problem [29].

Ultimately, the paper asserts that Neutrino FC is a key ingredient in modeling the birth rates and mass distributions of black holes and neutron stars.

Improvements for AI systems

AI System Improvements and Capabilities Based on the Paper

The AI system will be improved by integrating a probabilistic framework that maps progenitor characteristics to the probability of explosion/collapse, incorporating Neutrino Flavor Conversion (FC) as a deterministic factor.

Input Parameters: Zero-Age Main Sequence (ZAMS) mass (M ZAMS), Initial Core Compactness (xi 2.5), and Critical Baryon Density (rho c).
Improved Function: The AI can calculate the fraction of failed explosions (f fail) for a given M ZAMS, accounting for the non-linear impact of FC, especially within the critical 16–30 M range.
Output Capability: A predictive landscape (similar to Figure 1) that quantifies how much deeper flavor equilibration (rho c) increases shock suppression, allowing users to identify failure risk based on input parameters.

The AI will incorporate the specific physics governing the baryonic mass (M f) of the resulting compact object, distinguishing between success and failure modes.

Improved Function: The system accurately models how FC affects energy deposition behind the stalled shock, allowing it to simulate M f based on whether shock revival occurs.
Output Capability (Successful CCSNe): Predict a systematic reduction in M f when FC is active, providing results that align with observed low-mass neutron star populations (peaking around 1.2–1.4 M).
Output Capability (Failed/Black Hole Formation): Estimate the resulting baryonic mass (M f) when shock revival fails, quantifying the tendency for M f to be slightly larger due to sustained accretion.

The AI will incorporate a rigorous framework for handling known physical and observational uncertainties inherent in the current models.

Improved Function: The system allows users to adjust parameters (e.g., choice of Equation of State, e.g., SFHo vs others) and quantify how these variations affect the overall explosion rate, providing sensitivity analysis beyond a single fixed model.
Output Capability: A Confidence Metric for all predictions, explicitly stating how sensitive the predicted f fail is to:
The specific progenitor set used (e.g., Ref [12] vs. others).

*The degree of FC modeling (schematic vs. fully dynamic integration).

The AI will provide a precise mechanism-based explanation for the observed trends, linking the microphysics of flavor conversion directly to macroscopic outcomes.

Improved Function: The system can trace the energy flow: FC to Reduced Neutrino Energy Deposition to Suppressed Shock Revival.
Output Capability: Automatically identifying and highlighting specific progenitor models where FC converts a successful explosion into a failure, specifically detailing the corresponding change in M f for that particular mass range (16-30 M).

Abstract

The relative rate of neutron stars and black holes produced by the collapse of massive stars is highly uncertain. We simulate the stellar collapse of 195 progenitors with masses between 9, M and 120, M, incorporating a schematic treatment of neutrino flavor conversion. We find that flavor transformation reshapes the explodability of massive stars-especially in the 16 - 30, M mass range-and modifies the compact remnant mass distribution. Our findings identify neutrino flavor conversion as a fundamental ingredient in predicting neutron star and black hole populations, while naturally easing the red-supergiant and the supernova-rate problems, as well as reconciling theoretical expectations with the low-mass tail of the observed neutron star mass distribution.