REVIEW
Axions from Betelgeuse: Probing Axion Couplings with $^{23}\rm{Na}$ and $^{55}\rm{Mn}$
High Energy Physics - Phenomenology · Submitted 25 Oct 2026 · 46 references
Pith's verdict: Solid technical analysis of ALP production in Betelgeuse via 23Na and 55Mn, but the headline claim for the decay channel depends heavily on the debated assumption that Betelgeuse is near the end of core carbon burning.
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Referee report
The paper
The paper claims
Betelgeuse yields strongest astrophysical axion-proton limits at 155–440 keV
The reading
What carries the argument
The central mechanism is the production of mono-energetic ALPs via thermal de-excitation of excited nuclear states of 23Na (440.2 keV) and 55Mn (125.9 keV) in the hot interior of Betelgeuse. The ALP emission rate depends on the core temperature through the Boltzmann factor and on nuclear-structure parameters such as the ratio Γ_a/Γ_γ for M1 transitions. The ALPs then propagate to Earth and are detected either through conversion into photons in the Galactic magnetic field (for ultralight ALPs, using the formalism of Raffelt and Stodolsky) or through decay into two photons (for heavier ALPs, with a rest-frame decay rate proportional to g_{aγ}^2 $m_a^{3}$). The predicted photon signals are searched for in INTEGRAL-ISGRI and NuSTAR data using a binned likelihood analysis with profiled background models.
Extended reading notes
Core claim
The paper establishes new 95% CL upper limits on the product |g_aγ g_ap| (ALP-photon times ALP-proton coupling) using nuclear de-excitation of 23Na and 55Mn in Betelgeuse. For the decay channel, the 23Na line observed with INTEGRAL-ISGRI gives the strongest astrophysical constraint yet on |g_aγ g_ap| in the ALP mass range 155–440 keV, reaching 3.0×$10^{{-22}}$ $GeV^{{-1}}$ near 400 keV and improving on the combined M82 and neutron-star cooling bound. For magnetic-field conversion, the 23Na limits improve on previous 57Fe limits by two orders of magnitude but are still weaker than the SN 1987A bound. The 55Mn limits, though weaker than the 23Na ones, are considerably less sensitive to the uncertain evolutionary stage of Betelgeuse.
Load-bearing premise
The 23Na limits assume Betelgeuse is at the end of core carbon burning with a central temperature of about 95 keV; if Betelgeuse is instead in core helium burning (~15 keV), the limits weaken by up to a factor of 5×$10^{6}$ (five orders of magnitude).
Editorial extensions
If this is right
- The 23Na decay limits become the strongest astrophysical constraint on the ALP-proton coupling product |g_aγ g_ap| for ALP masses between 155 and 440 keV, surpassing the combined M82 and neutron-star cooling bound.
- The 55Mn limits, although weaker, are more robust against uncertainties in Betelgeuse's evolutionary stage, providing a reliable floor on the coupling in the mass range up to 124 keV.
- The magnetic conversion limits from 23Na improve on previous 57Fe limits by two orders of magnitude in the ultralight mass regime, though they are still weaker than the SN 1987A bound.
- The method demonstrates that a single nearby evolved star can host multiple independent ALP searches covering many decades in mass, using only archival X-ray and gamma-ray data.
- Future MeV astronomy instruments such as COSI or newASTROGAM could extend the sensitivity significantly in both the magnetic conversion and decay channels.
Reading between the lines
- If Betelgeuse is independently confirmed to be in core carbon burning (e.g., through asteroseismology or neutrino detection), the 23Na limits become a benchmark for the ALP-proton coupling in the sub-MeV mass range, potentially motivating laboratory searches such as resonant absorption in NaI detectors.
- The same technique applied to other nearby supergiants with different core temperatures could probe different mass windows and reduce the stellar-model dependence, creating a grid of complementary constraints.
- Combining the 23Na (proton-sensitive) and 57Fe (neutron-sensitive) limits from the same star could, in principle, disentangle the ALP-proton and ALP-neutron couplings, though both channels have different systematic uncertainties.
Original abstract
We investigate axion-like particle (ALP) production in the interior of Betelgeuse via nuclear de-excitation of thermally populated excited states of $^{23}$Na and $^{55}$Mn. As these ALPs propagate to Earth, they can produce photons either through their conversion in the Galactic magnetic field or through their decay. Using INTEGRAL-ISGRI and NuSTAR observations, we search for these photon signals, find no significant excess, and derive 95% CL exclusion limits on the ALP couplings. For magnetic-field conversion of ALPs, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI constrains $|g_{a\gamma}g_{ap}| < 4.1\times10^{-21}$ ($6.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ for $m_a < 10^{-10} \mathrm{eV}$. For ALP decays, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI (NuSTAR) constrains $|g_{a\gamma}g_{ap}|$ down to $3.0\times10^{-22}$ ($2.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ at $m_a \simeq 400$ ($83$) keV, weakening in both cases as $m_a^{-3/2}$ for lower ALP masses, and as $m_a^{-2}$ for $^{23}$Na below $m_a \sim 1$ keV, with sensitivity extending to $m_a \simeq 440.2$ ($124$) keV. Although our $^{23}\mathrm{Na}$-based limits are the strongest for both channels, their larger transition energy makes them more sensitive to the precise evolutionary stage of Betelgeuse, whereas the $^{55}\mathrm{Mn}$-based limits are considerably more robust against such uncertainties.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We investigate axion-like particle (ALP) production in the interior of Betelgeuse via nuclear de-excitation of thermally populated excited states of $^{23}$Na and $^{55}$Mn. As these ALPs propagate to Earth, they can produce photons either through their conversion in the Galactic magnetic field or through their decay. Using INTEGRAL-ISGRI and NuSTAR observations, we search for these photon signals, find no significant excess, and derive 95% CL exclusion limits on the ALP couplings. For magnetic-field conversion of ALPs, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI constrains $|g_{a\gamma}g_{ap}| < 4.1\times10^{-21}$ ($6.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ for $m_a < 10^{-10} \mathrm{eV}$. For ALP decays, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI (NuSTAR) constrains $|g_{a\gamma}g_{ap}|$ down to $3.0\times10^{-22}$ ($2.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ at $m_a \simeq 400$ ($83$) keV, weakening in both cases as $m_a^{-3/2}$ for lower ALP masses, and as $m_a^{-2}$ for $^{23}$Na below $m_a \sim 1$ keV, with sensitivity extending to $m_a \simeq 440.2$ ($124$) keV. Although our $^{23}\mathrm{Na}$-based limits are the strongest for both channels, their larger transition energy makes them more sensitive to the precise evolutionary stage of Betelgeuse, whereas the $^{55}\mathrm{Mn}$-based limits are considerably more robust against such uncertainties.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We investigate axion-like particle (ALP) production in the interior of Betelgeuse via nuclear de-excitation of thermally populated excited states of $^{23}$Na and $^{55}$Mn. | contribution 0.98 | 0.77 | 0.04 | asserted 0.91 |
| s1 | As these ALPs propagate to Earth, they can produce photons either through their conversion in the Galactic magnetic field or through their decay. | background 0.64 | 0.06 | 0.03 | hedged possibility 0.98 |
| s2 | Using INTEGRAL-ISGRI and NuSTAR observations, we search for these photon signals, find no significant excess, and derive 95% CL exclusion limits on the ALP couplings. | result 0.75 | 0.98 | 0.64 | asserted 1.00 |
| s3 | For magnetic-field conversion of ALPs, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI constrains $|g_{a\gamma}g_{ap}| < 4.1\times10^{-21}$ ($6.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ for $m_a < 10^{-10} \mathrm{eV}$. | result 1.00 | 0.92 | 0.22 | asserted 1.00 |
| s4 | For ALP decays, the $^{23}\mathrm{Na}$ ($^{55}\mathrm{Mn}$) line observed with INTEGRAL-ISGRI (NuSTAR) constrains $|g_{a\gamma}g_{ap}|$ down to $3.0\times10^{-22}$ ($2.9\times10^{-19}$) $\mathrm{GeV}^{-1}$ at $m_a \simeq 400$ ($83$) keV, weakening in both cases as $m_a^{-3/2}$ for lower ALP masses, and as $m_a^{-2}$ for $^{23}$Na below $m_a \sim 1$ keV, with sensitivity extending to $m_a \simeq 440.2$ ($124$) keV. | result 1.00 | 0.94 | 0.32 | asserted 1.00 |
| s5 | Although our $^{23}\mathrm{Na}$-based limits are the strongest for both channels, their larger transition energy makes them more sensitive to the precise evolutionary stage of Betelgeuse, whereas the $^{55}\mathrm{Mn}$-based limits are considerably more robust against such uncertainties. | interpretation 0.83 | 0.63 | 0.18 | asserted 0.99 |
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Figures
Figures reproduced from arXiv:2610.34540 by the authors.
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Discussion
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