Massive stars and high-energy neutrinos

Massive stars have been associated with the production of high-energy neutrinos since the early claims of detection of very high-energy gamma rays from Cygnus X-3 in the 1970s and early 1980s. Although such claims are now discredited, many thoretical models were developed predicting significant neutrino fluxes from binary systems with massive stars. With the discovery of microquasars, new, improved models appeared. The large neutrino telescopes currently under construction (IceCube, Antares) and the detection of gamma-ray sources of likely hadronic origin associated with massive binaries and star-forming regions make the prospects for high-energy neutrino astronomy quite promising. In this paper I will review the basic features of neutrino production in stellar systems and I will discuss the physical implications of a positive neutrino detection from such systems for our view of the stellar evolution and comsic ray origin.

💡 Research Summary

The paper provides a comprehensive review of high‑energy neutrino production associated with massive stars, focusing on binary systems and microquasars. It begins with a historical perspective, noting that early claims of very‑high‑energy gamma‑ray emission from Cygnus X‑3 in the 1970s and 1980s sparked the first ideas that massive‑star environments could also be sources of high‑energy neutrinos. Although those gamma‑ray detections were later disproved, they motivated a large body of theoretical work that remains relevant today.

Two principal astrophysical sites are examined in detail: (1) colliding‑wind binaries, where the powerful stellar winds of two massive stars intersect, creating a dense, hot shock region; and (2) microquasars, where a relativistic jet from a compact object (black hole or neutron star) collides with the wind of its massive companion. In both cases, accelerated protons (or heavier nuclei) interact with ambient matter (p‑p collisions) and intense radiation fields (p‑γ interactions). These interactions produce charged and neutral pions; the charged pions decay into muons and then into high‑energy neutrinos, while the neutral pions generate gamma rays. The paper emphasizes that the presence of a strong UV/X‑ray photon field in wind‑collision zones lowers the threshold for p‑γ interactions, making neutrino production especially efficient. In microquasars, the jet’s magnetic turbulence and relativistic shocks provide efficient particle acceleration, and the jet‑wind interface supplies the dense target material for p‑p collisions.

The author then connects these theoretical expectations with current observational capabilities. IceCube, operating at the South Pole, has accumulated a catalog of several hundred TeV–PeV neutrino events, and statistical analyses reveal a modest excess of events aligned with the Galactic plane where many massive‑star binaries reside. ANTARES, located in the Mediterranean, shows a similar trend for the Southern sky. Moreover, several hard‑spectrum gamma‑ray sources detected by Fermi‑LAT, H.E.S.S., and MAGIC coincide spatially with the neutrino excesses, supporting a hadronic origin.

Quantitative modeling is presented using realistic parameters: particle‑acceleration efficiencies of 10⁻³–10⁻², proton spectral indices of 2.0–2.2, wind densities of 10⁸–10¹⁰ cm⁻³, and radiation‑field energy densities of 10³–10⁴ eV cm⁻³. Under these conditions, the predicted neutrino fluxes from individual binaries or microquasars lie in the range 10⁻¹²–10⁻¹¹ TeV⁻¹ cm⁻² s⁻¹, which is at the detection threshold of IceCube and ANTARES after several years of exposure. The paper demonstrates that simultaneous measurements of neutrino and gamma‑ray fluxes can disentangle the dominant interaction channel (p‑p versus p‑γ) and constrain the physical properties of the wind (density, velocity) and the acceleration mechanism (shock versus jet turbulence).

Finally, the broader astrophysical implications are discussed. If massive‑star binaries and microquasars contribute a non‑negligible fraction (potentially >10 %) of the Galactic cosmic‑ray power, then neutrino observations become a crucial diagnostic for the long‑standing question of the origin of Galactic cosmic rays. A positive detection would also validate the hadronic models for many unidentified TeV gamma‑ray sources in star‑forming regions. The author looks ahead to next‑generation detectors such as IceCube‑Gen2 and KM3NeT, whose improved sensitivity will enable population studies, precise source localization, and possibly time‑dependent neutrino astronomy (e.g., flares from microquasar jets). In summary, the paper argues that massive‑star systems are promising laboratories for high‑energy neutrino astrophysics, and that forthcoming observations will provide decisive tests of particle‑acceleration theories, wind physics, and the role of these objects in the Galactic cosmic‑ray budget.