Positron accumulations from stellar nucleosynthesis

1 Introduction

There are many unresolved questions presented by Earth’s nearest companion star, the Sun. These include the mechanisms behind the solar cycle, solar flares, sunspots, and solar energetic particles (SEP). Adequately resolving these questions in our Sun could help explain other unresolved observations in astronomy, including intergalactic cosmic rays, distant star behaviors, galaxy development, and the observed abundance of heavy elements. To help solve these questions and more, it is practical to explore unconventional ideas.

For this study, we examine whether departures from the assumption of short-lived antimatter could provide insight into some of these outstanding questions. In an electron-depleted environment, positrons could survive indefinitely. Without electrons and with ongoing fusion reactions, positrons also could accumulate.

Positrons are the antimatter equivalent to an electron. First posited to exist by Dirac (1928), they were later proven experimentally by Anderson (1932). Positrons are a relatively common by-product of nuclear decay, but they can also be formed in other manners, including pair production and nuclear fusion. Nuclear fusion, in this case through stellar nucleosynthesis, will be the focus of this study.

In matter-dominated environments, antimatter is inherently short-lived due to rapid annihilation with surrounding normal matter. Whenever a positron and electron come into contact, their interaction typically results in annihilation, with caveats. This annihilation event is very well understood and produces two well-defined 511 keV photon emissions. This is the conventional expectation; that the production of antimatter quickly leads to its destruction from the abundant normal matter in the environment.

There is no existing method to observe or detect an accumulation of electron-segregated positrons below a stellar surface. The positrons’ charge would be the same as the numerous protons in the core. Their interaction with particles outside of electrons would have almost no perceivable indicators on the stellar surface. Photons produced by internal stellar annihilation events are repeatedly absorbed and scattered, effectively erasing information about their initial energies. However, from our understanding of stellar nucleosynthesis, it can be inferred that the quantity of positrons produced approaches the quantity of neutrinos produced. Neutrinos are emitted by the Sun in an extremely high flux, and these can be observed through neutrino counting.

The Sun’s layers include the central core, the radiative zone, the convection zone, the photosphere, the chromosphere, and then outer corona (Priest, 2014). The radiative zone and convection zone are separated by the tachocline, a boundary region between the differentially rotating regions. The Sun is well described as a quasi-neutral plasma composed primarily of hydrogen and helium ions alongside charge-balancing electrons (Gopalswamy, 2020). Fusion reactions primarily occur in its dense core, where positron production is likewise concentrated.

The Proton-Proton Fusion Chain (pp-chain) in our Sun fuses 3.34 × 10⁺³⁸ protons per second (Mullan, 2023; Loveland and Seaborg, 2017). Each fusion produces a positron and an electron neutrino by-product, as shown in Figure 1, and can also be expressed in the equation (p + p → d + e ^**+** + ν _**e**). This is equivalent to approximately 1.67 × 10⁺³⁸ positrons/neutrinos per second from the pp-chain alone (Mullan, 2023; Loveland and Seaborg, 2017). We can observe the neutrinos on Earth where we receive a dose of approximately 6 × 10⁺¹⁰ neutrinos/cm²/sec (Mullan, 2023; Suzuki, 2020). That is over a trillion neutrinos passing through one square centimeter every 17 s. Furthermore, this is the dose at a large distance of roughly 150 million kilometers away from the Sun. With this massive quantity of neutrinos, consider that there is an equal number of positrons being created in the Sun’s core, yet they are rarely observed. While nearly all the neutrinos escape the Sun and then flood the Earth with a shower of neutrino particles, each of the positrons is conventionally expected to annihilate with an electron from the solar environment (Gopalswamy, 2020). Though only neutrinos are regularly observed, the high production rate of both particles motivates further investigation into the possibility of localized stellar positron populations.

Other reactions in stellar nucleosynthesis also produce positrons and neutrinos together similar to the pp-chain, however the majority of positrons are produced in this foundational first chain. Other positron/neutrino producing reactions include the pp-III branch’s ⁸Be production (referred to as ⁸B neutrinos), the pp-IV (hep) branch’s ⁴He production, and ¹³N and ¹⁵O reactions in the carbon-nitrogen-oxygen (CNO) cycle (Suzuki, 2020; Davis, 2003). There are other processes that only produce neutrinos, but also some that only produce positrons. For instance, there are low quantities of positrons produced through beta decay of isotopes. In some high-energy environments within stars, pair production of an electron and positron can occur from high-energy photons. As this reaction is producing both opposite particles, it has a lower likelihood of contributing to an increasing positron population. As the pp-chain dominates production, the overall quantity of neutrino and positron production is similar.

The objective of this initial work is not to demonstrate that long-lived stellar positron accumulations have been established, but rather to identify plausible mechanisms, observational consequences, and falsifiable predictions that can be evaluated by future theoretical modeling and high-energy observations.

2 Observational implications and astrophysical context

If the solar core is ever locally deprived of electrons, then there is a potential for an antimatter accumulation in the form of positrons. Electron deprivation mechanisms may result from a combination of continuous annihilation events near positron production, local electric or magnetic field properties, or other unique circumstances in the solar core. In this theoretical situation, regions might develop that are composed of normal matter ions and positrons residing without electrons. It is unclear what the consequences of large antimatter accumulations might be, but changes in the electric and magnetic fields or other anti-matter inclusive HED physics would be expected. Predictions would include observation of the annihilation line from stars and high energy emissions, as well as nucleosynthesis rate adjustments. An improved understanding of stellar functions could aid in the prediction of solar weather, further increasing the understanding of phenomenon such as the solar cycle, solar flares, and sunspots.

An ongoing question in solar physics is the detailed mechanism underlying the 11-year solar cycle (Kallenrode, 2004). The cycle is understood to arise from magnetohydrodynamic processes involving the coupling of plasma flows and magnetic fields within the solar interior (Gizon, Birch and Spruit, 2010). While this large-scale behavior can be described by dynamo theory, the role of microphysical processes in modulating these dynamics remains an area of active study. Positrons produced in nuclear reactions within the solar core are conventionally expected to annihilate rapidly, depositing energy locally into the surrounding plasma. Although they are not known to contribute to large-scale charge separation or particle transport, their continuous production and annihilation represent a persistent, localized source of energy. It is therefore worth considering whether such microphysical energy inputs could contribute to variations in plasma properties that influence magnetic field generation, flux emergence, or other processes associated with the solar cycle. Positron annihilation has been widely observed in solar flares (Chupp, Forrest and Suri, 1973; Murphy, Share, Skibo and Kozlovsky, 2005; Fleishman, Altyntsev and Meshalkina, 2013), providing direct evidence of positron production in high-energy solar environments. These positrons are assumed to be produced locally during flare-associated particle acceleration, rather than transported from the solar core. This suggests that positrons are naturally present in high-energy solar environments, motivating consideration of whether their associated energy deposition could influence the plasma conditions underlying flare activity.

If particles would have to pass through an electrical potential difference over a long distance, there is logic for acceleration towards high energies. Accelerations in solar flares, particularly characteristic of positively charged ions, have been observed and researched in recent literature (Drake, et al., 2009; Russell, Polito, Testa, De Pontieu and Belov, 2025). In some cases, these positively charged ions reach extreme velocities (Russell, Polito, Testa, De Pontieu and Belov, 2025). One might consider the similarities to a particle accelerator, where positively charged particles could be accelerated towards a negatively charged region. In the case of a positively charged solar core, the positrons might find a path of low-density electrons around magnetic field lines, leading towards an opportunity for acceleration outwards to a more negatively charged region. In some cases, this might reach the surface in a solar flare.

Solar sunspots are also a candidate for positron presentation related to the previously discussed solar flares that typically erupt in proximity to sunspots. Sunspots are considered to be sourced from deep within the sun and anchored to the tachocline, the boundary region between the radiative and convective zones (Gizon, Birch and Spruit, 2010). The proposed positron accumulations would be expected deeper toward the solar core, and therefore sunspots could be a potential mechanism to present such material outward.

Beyond the Sun, there are increasing observations of positron production throughout the galaxy. Pulsars are producing high energy positrons in excess of 10 GeV (Harding, 1987). The gamma ray burst referenced as the BOAT (Brightest of All Time), has high-confidence positron annihilation emission lines (Burns et al., 2023; Ravasio, 2024). This high energy emission could provide additional clues into the role of positrons in stellar processes.

The Milky Way Galaxy itself holds a long-standing observational puzzle in the form of a massive 511 keV annihilation line toward the galactic center bulge region (Frontera, et al., 2021; Kierans, et al., 2020). It is one of the most relevant issues of modern astro-physics with a galaxy-wide flux of approximately 2.7 × 10⁻³ photons/cm²/s amounting to a positron annihilation rate of 5 × 10⁺⁴³ electrons per second (Frontera, et al., 2021; Prantzos, et al., 2011). In this case, small percentages of the photons have been attributed to radioactive decay, however, most of the sources remain unknown. The relevance of where this source originates could be the numerous stars producing positrons. If stellar interiors supply a significant portion of galactic positrons, the resulting annihilation radiation should mirror evolved stellar populations rather than isolated compact objects or radioactive areas.

A positron population could also be relevant in the context of the “cosmological lithium problem.” This long-standing discrepancy in the predictions of Big Bang Nucleosynthesis (BBN) presents a higher abundance of lithium than what has been observed in stellar atmospheres (Fields, 2011). Formation of ⁷Li proceeds primarily through the electron-capture reaction from ⁷Be in both BBN and stellar nucleosynthesis (O'Malley, et al., 2011; Loveland and Seaborg, 2017). Electron-capture depends on local plasma conditions that include temperature, ionization state, and importantly electron density. If there is a decrease in the electron density, or if there are local positron accumulations, then the production rate of lithium through electron-capture should also decrease in stellar nucleosynthesis. This decreased production throughout the ongoing galactic chemical evolution could result in the lower lithium abundance observed in stellar atmospheres.

In further consideration of galactic chemical evolution, there is also a longstanding question around the abundance of the p-nuclei, and how they are synthesized in nature (Rauscher, 2010). These are proton rich isotopes that are not derived in such observed abundance from the standard nucleosynthesis processes. It has been hypothesized that they could be formed through positron-capture (Reeves and Stewart, 1965). Again, in a positron rich stellar interior, application of this theory could explain the abundance of p-nuclei. This potentiality also opens the door to additional antimatter inclusive nucleosynthesis processes.

Proceeding to observational potentials, the production of ⁷Li in stellar environments also provides a potential probe of plasma conditions in stellar interiors. Electron-capture reactions involving ⁷Be produce neutrinos with characteristic energies, making them sensitive to the local thermodynamic state of the plasma. While electron densities in stellar cores are expected to remain sufficiently high enough that capture processes proceed efficiently, small variations in plasma conditions can still influence reaction rates at a measurable level. Neutrino observations continue to provide important constraints on solar models, including those involving ⁷Be and ⁸B neutrinos, where uncertainties remain at the level of several tens of percent (Bahcall and Serenelli, 2005). Continued refinement of these measurements, alongside improved modeling of plasma effects, may help further constrain the conditions under which these reactions occur, and by extension, the role of microphysical processes such as positron production and annihilation.

A pathway for accumulated positrons to present outside of the stellar interior could come from low-mass X-ray binary stars (LMXBs) (Kierans, et al., 2020; Frontera, et al., 2021). These are typically characterized as a dense black hole or neutron star pulling material away from a neighboring star. In a situation where a star’s core is composed of standing positron populations, pulling away outer layers could expose deeper stellar layers that, if they contain long-lived positron populations, would be expected to exhibit enhanced annihilation signatures.

Furthermore, it could be reasoned that some large energy bursts from stars and supernova could be attributed to large-scale mixture of matter and antimatter. In the event of a stars collapse, if there is a large presence of antimatter, the sudden exposure to the exterior normal matter could lead to a presentable annihilation event. From observations of core collapse supernova, it has been shown that these explosions form two regions of perpendicularly polarized photons (Nagao, et al., 2024). As positron/electron annihilation similarly forms perpendicularly polarized photons, the observation could further present evidence that is closely related to antimatter accumulations (Ivashkin, et al., 2023).

Stellar mechanisms that could allow for local positron accumulations are being investigated. Modeling of magnetic and electric field dynamics to investigate local environments that may favor positively charged particles is one key area. The variability of a plasma’s electron density in a magnetic field has been studied and found to increase or decrease with the proximity to the field lines (Park, Lee, Go and Chung, 2025; Khaleeq-ur-Rahman, Bhatti, Rafique, Latif and Chaudhary, 2009). Favored regions could exist along field lines or could expand during regular solar pole flips. Layered zones of alternating charge have consistently been observed in plasmas under varying circumstances, appealing to this potential (Cornolti, Ceccherini, Betti and Pegoraro, 2005; Economou, 2007; Kolobov and Economou, 1997; Kushner, 2003; Sternberg, Godyak and Hoffman, 2006).

Long-term electron escape from the surface, due to the low mass and high energy of these particles, could lead to electron depletion that then positively charges the outer solar layers (Cornolti, Ceccherini, Betti and Pegoraro, 2005; Malheiro, Ray and Zanchin, 2003; Halekas, et al., 2020; Halekas, et al., 2021; Halekas, et al., 2022). With a more positive surface charge, electron migration downward into lower strata is restricted. Classical studies have also modeled a star in such a way that electrons are likely to rise to the outer regions simply due to their lower mass in comparison to other ions in the environment, thus depleting the core (Eddington, 1926; Malheiro, Ray and Zanchin, 2003). Furthermore, continuous electron annihilation rates, locally within the positron producing core, are being evaluated over extremely long timespans to determine possible depletion rates through exhaustion.

Immediate applications for this mechanism could include improving models for solar activity and subsequent weather events. It could also present a new outlook on HED plasma processes that consider the inclusion of anti-matter. For instance, there are potential positron relevant nucleosynthesis processes that are not thoroughly explored, such as positron capture for heavier elements. Perhaps there is a chance for even further antimatter relevant chains in stellar nucleosynthesis. HED physics application of a standing positron population could lead to a better understanding of new processes and field configurations in large plasmas. As plasmas are a notoriously difficult study, the possibility of sustained antimatter populations within an ion field could radically alter stellar models used in a variety of star types. An example could be the effects of reduced electron screening during fusion reactions (Gillespie, et al., 2025). Behaviors of positively charged ion/positron populations in a plasma can further inform star behaviors during different parts of their lifetime, aiding in space weather understanding.

Matter-antimatter annihilation represents the most efficient known mechanisms for converting mass into radiation. While energy extraction from stellar interiors is not currently feasible, the annihilation process highlights the extreme energy densities available. Even small quantities of matter–antimatter interaction correspond to substantial energy release, making positrons of interest in both astrophysical and laboratory plasma contexts. Further theoretical application of positron populated stellar interiors could also aid in the study of dark matter, baryon asymmetry, black hole formation, supernova initiation, and more.

Future observational efforts should focus on identifying signatures that distinguish long-lived stellar positron populations from conventional positron production mechanisms. While temporary 511 keV emission from solar flares and compact objects are well-known, discovering continuous or repeating positron annihilation in quiescent stars, interacting binaries, or specific evolutionary stages would confirm the presence of long-lived stellar positron reservoirs. Observing the 511 keV line profile, photon polarization, and related neutrino signals can help differentiate between positrons that undergo prolonged confinement before annihilating and those that annihilate shortly after being accelerated. Future MeV gamma-ray observatories could directly test these observational predictions.

3 Discussion

In this paper, we have discussed the potential ramifications of antimatter accumulations in the form of positrons within stellar cores. The nature of positrons, the solar composition, and solar nucleosynthesis were reviewed. Observational evidence of positron annihilation was studied and applied to theoretical positron accumulations in stars and our galaxy. Early review of mechanisms for positron accumulation were presented. Applications of antimatter accumulations are also discussed with respect to HED physics and energy.

Positron accumulation could contribute to our understanding of solar cycle related phenomena that are important for the prediction of space weather. Refined modeling these events is of paramount concern as the fragility of modern technological systems has increased. Close review of the predictions and their relevance to positrons is suggested, along with future computational models that incorporate such behavior. These areas of study could lead to new HED applications, more resilient space infrastructure, and a greater understanding of the solar system, galaxy, and universe.

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Footnotes

Edited by: Douglas Alexander Singleton, California State University, Fresno, United States

Reviewed by: Oem Trivedi, Ahmedabad University, India

Amar Aryan, National Central University Graduate Institute of Astronomy, Taiwan