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Neutrino Constraints on memory-burdened Primordial Black Holes from Dwarf Spheroidal Galaxies

Using 10 years of IceCube muon-track data from 14 dwarf spheroidal galaxies, this study finds no evidence of neutrino signals from memory-burdened primordial black holes and establishes improved upper limits on their abundance fraction, particularly for the $k=1$ case.

Original authors: Xiu-Hui Tan, Jun-qing Xia, Yu-Feng Zhou

Published 2026-06-16

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CC BY 4.0

Original authors: Xiu-Hui Tan, Jun-qing Xia, Yu-Feng Zhou

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 Idea: Hunting for "Ghostly" Black Holes

Imagine the universe is filled with invisible "dark matter" that holds galaxies together. Scientists have a wild theory: maybe this dark matter isn't made of mysterious particles, but of Primordial Black Holes (PBHs). These are tiny black holes that formed in the very first split-second after the Big Bang.

Usually, we think black holes are eternal. But according to physics, they actually "evaporate" like a melting ice cube, shooting out particles as they shrink. The problem is, if they were too small, they would have melted away billions of years ago.

The Twist: The "Memory Burden"
This paper introduces a new idea called the "Memory Burden" effect. Think of a black hole as a hard drive. As it evaporates, it loses mass, but it also has to "process" all the information (memory) it stored.

Normal Evaporation: The black hole melts fast.
Memory Burden: Once the black hole loses about half its weight, it gets "stuck" in a traffic jam of its own memories. The information it holds pushes back, slowing down the melting process significantly.
The Result: This allows even very light black holes (some as light as a mountain) to survive until today, potentially making up our dark matter.

The Detective Work: Listening for a Whisper

If these "memory-burdened" black holes are still around and slowly evaporating, they should be shooting out high-energy neutrinos.

What are neutrinos? They are "ghost particles." They can pass through planets, stars, and people without hitting anything. They are incredibly hard to catch.
The Detector: The scientists used IceCube, a massive detector buried deep in the Antarctic ice. It's like a giant net made of sensors waiting to catch a ghost particle.

The Strategy: The "Quiet Neighborhoods"

To find these ghostly signals, the team looked at Dwarf Spheroidal Galaxies (dSphs).

The Analogy: Imagine you are trying to hear a single person whispering in a crowded stadium. It's impossible because of the noise. But if you go to a library where no one is talking, that whisper becomes clear.
Why dSphs? These are tiny, lonely galaxies that are packed with dark matter but have almost no stars or gas to create "noise" (background radiation). They are the perfect "libraries" for listening to dark matter whispers.

The Investigation: What They Did

The Data: They looked at 10 years of data from IceCube, specifically tracking "muon-tracks" (paths left by particles created when a neutrino hits something).
The Targets: They focused on 14 specific dwarf galaxies. They gathered data from four different scientific studies to get the most accurate map of how much dark matter is in each galaxy (this map is called the "D-factor").
The Search: They ran a complex statistical check (a "likelihood analysis") to see if there were more neutrinos coming from these galaxies than expected by random chance.

The Results: The Silence Speaks

The bad news: They found no excess signal. They didn't hear the whisper. The number of neutrinos they saw was exactly what you'd expect from random background noise.

The good news (The Constraints): Even though they didn't find the black holes, they learned something very important by not finding them.

The Analogy: Imagine you are looking for a specific type of rare bird in a forest. You don't see any. You can't say the bird doesn't exist, but you can say, "If this bird exists, it can't be more common than 1 in a million, or we would have seen it."
The Findings:
- Case 1 (k=1): If the "memory burden" slows the black holes down moderately, the scientists can now rule out that these black holes make up all the dark matter for a wide range of masses (up to about $10^{10}$ grams). This is a much stricter limit than previous studies.
- Case 2 (k=2): If the memory burden slows them down a lot (k=2), the black holes emit so few neutrinos that IceCube isn't sensitive enough to see them yet. The limits here are weaker.
- The Power of Teamwork: By combining the data from all 14 galaxies, they got a much clearer picture than looking at just one. It's like having 14 people listening in the library instead of just one; the chance of missing a whisper drops significantly.

The Bottom Line

This paper didn't find the "memory-burdened" black holes, but it successfully tightened the net. It proved that if these black holes exist and make up our dark matter, they must be much rarer or have different properties than we previously thought (specifically for the "moderate slowdown" scenario).

The authors suggest that future, bigger detectors (like IceCube-Gen2) will be needed to catch the faint signals from the "heavy slowdown" (k=2) scenario, but this study has set a very strong foundation for that future hunt.

Technical Summary: Neutrino Constraints on Memory-Burdened Primordial Black Holes from Dwarf Spheroidal Galaxies

Problem Statement
Primordial Black Holes (PBHs) formed from early-universe overdensities remain compelling dark matter (DM) candidates. However, standard semi-classical Hawking evaporation predicts that PBHs with masses below $\sim 5 \times 10^{14}$ g would have evaporated by the present epoch. Recent theoretical developments regarding the "memory burden" (MB) effect—arising from the black hole quantum information paradox—suggest that PBH evaporation rates can be significantly suppressed once a PBH loses approximately half its initial mass. This mechanism extends the viable mass window for PBHs as DM candidates down to $\sim 10^4$ g. While these memory-burdened PBHs are expected to emit high-energy particles, including neutrinos, their specific signatures have not been comprehensively searched for using current neutrino observatory data. Dwarf spheroidal galaxies (dSphs), characterized by high DM content and low astrophysical backgrounds, serve as ideal targets for such indirect detection searches.

Methodology
The authors conduct a search for neutrino signals from memory-burdened PBHs using 10 years of publicly available muon-track data from the IceCube Neutrino Observatory (April 2008–July 2018). The analysis focuses on 14 dSphs common to four independent literature sources providing Dark Matter (D-factor) measurements:

GS set: Geringer-Sameth et al., utilizing uniform Jeans modeling.
E set: Evans et al., employing simple analytic formulae.
P set: Pace & Stigari, using empirical scaling relations.
C set: LHAASO collaboration, providing updated constraints.

The study employs an unbinned maximum-likelihood analysis to evaluate the significance of potential PBH neutrino emission. The likelihood function incorporates:

Signal Model: Neutrino flux derived from the memory-burdened PBH evaporation spectrum, calculated using the BlackHawk 2.30 code. The model accounts for the suppression factor $k$ (where $k=1$ and $k=2$ are tested) and the parameter $q$ (defining the transition to the MB phase, typically $q=0.5$ ).
Flavor Oscillation: The analysis assumes a flavor-unbiased initial flux ( $1:1:1$ ) and applies Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing to determine the flux at Earth, though the total event rate is noted to be independent of specific mixing angles.
D-factor Treatment: To handle uncertainties in DM distributions, the authors utilize a profile likelihood framework with an asymmetric Gaussian prior for the D-factors, allowing for independent error treatment across the 14 dSphs.
Statistical Framework: A test statistic (TS) based on the likelihood ratio is used to compare the background-only hypothesis against the PBH signal hypothesis.

Key Contributions

Comprehensive Dataset: The work compiles a robust sample of 14 dSphs by cross-referencing four independent D-factor datasets, addressing the variability in astrophysical modeling.
Memory Burden Application: This is the first application of the memory burden effect to neutrino searches from dSphs using IceCube data, specifically testing the $k=1$ and $k=2$ suppression scenarios.
Joint Analysis: The paper implements a combined analysis of all 14 dSphs, demonstrating that independent error treatment effectively reduces statistical uncertainties compared to single-source analyses.

Results

Null Detection: No significant excess of neutrino events over the background-only hypothesis was detected in the 10-year IceCube dataset.
Upper Limits on Abundance ( $f_{PBH}$ ):
- $k=1$ Case: The analysis yields significantly improved upper limits on the PBH abundance fraction compared to previous studies. For $k=1$ , the combined analysis excludes PBHs as the dominant component of DM up to masses of approximately $10^{10}$ g. The constraints are particularly tight for PBH masses between $10^7$ and $10^{10}$ g, where the neutrino spectra align well with IceCube's sensitivity.
- $k=2$ Case: Constraints are less restrictive due to the strong entropy suppression reducing the neutrino flux in the energy range where IceCube is most sensitive.
Dataset Comparison: The C set (LHAASO) generally provides the strongest constraints due to higher D-factor values, while the GS and E sets still yield tighter limits than previous literature even under conservative assumptions.
Individual vs. Combined: The joint analysis of all 14 dSphs produces substantially tighter exclusion limits across the parameter space than any individual dSph analysis.

Significance
The paper establishes that neutrino searches from dSphs provide competitive and, in the $k=1$ scenario, superior constraints on memory-burdened PBHs compared to previous gamma-ray and cosmic-ray studies. The authors claim that their results robustly demonstrate that for $k \lesssim 1.3$ (or $k \lesssim 1.5$ with the combined dataset), PBHs cannot constitute the entirety of dark matter up to $\sim 10^{10}$ g. While constraints on lower mass PBHs remain less stringent than existing limits, the analysis highlights the growing sensitivity of neutrino detectors to the harder spectra associated with more massive PBHs under the MB framework. The work provides a methodological foundation for future searches using next-generation instruments like IceCube-Gen2, which are expected to further probe the $k=2$ scenario and extend mass reach.