In the realm of energy and particle physics, a team of researchers from the University of Torino, the University of Hamburg, the University of Amsterdam, and the National Institute for Astrophysics (INAF) in Italy, led by Saurabh Mittal, has been delving into the mysterious world of axion-like particles (ALPs). These hypothetical particles are of great interest in the energy sector due to their potential role in dark matter and their possible applications in energy storage and transfer.
The research team has been focusing on the search for ALPs from nearby pre-supernova stars. These stars, in the late stages of their evolution, provide an ideal environment for the production of ALPs due to their high core temperatures and densities. The researchers utilized the full public 22-year INTEGRAL/SPI dataset to search for a combined signal of ALP-induced hard X-ray and soft gamma-ray emission from 18 nearby pre-supernova stars.
The team constructed individual stellar spectra and linked them in a coherent analysis. They used a maximum-likelihood approach to extract fluxes in the 20-2000 keV energy range. Stellar evolution models were employed to obtain the expected spectral shapes of ALP production processes, which peak between 50-500 keV, depending on the star’s mass and evolutionary stage.
The researchers constructed a joint likelihood that incorporates uncertainties in stellar parameters to derive combined constraints on the coupling constants gaγ and gae as a function of the ALP mass ma. The hard X-ray and soft gamma-ray fluxes of all selected stars were consistent with zero within uncertainties. The team provided upper limits on the continuum emission and on the 511 keV and 1809 keV line fluxes.
The combined upper limit on gaγ × gae was found to be (0.008 – 2) x 10^-24 GeV^-1 (95% C.I.), while the ALP-photon coupling was constrained to gaγ = (0.13 – 1.26) x 10^-11 GeV^-1 (95% C.I.) for ma ≤ 10^-11 eV, depending on the time to core collapse and magnetic field assumptions. Conservative limits of (0.27 – 1.25) x 10^-24 GeV^-1 (95% C.I.) were obtained assuming all but one star were in the early He-burning phase.
These results, published in the journal Physical Review D, rank among the strongest limits on ALP couplings to date. They demonstrate the importance of soft gamma-ray observations for probing ALPs and massive star evolution. While the practical applications for the energy sector are still speculative, the understanding and manipulation of ALPs could potentially revolutionize energy storage and transfer technologies, making this an exciting area of research to watch.
In the meantime, the energy industry can benefit from the advanced data analysis techniques and stellar evolution models used in this research. These tools can be adapted to improve energy forecasting, resource management, and the development of new energy technologies. As our understanding of the universe continues to grow, so too will the potential for innovative energy solutions.
This article is based on research available at arXiv.