Leading astronomers have identified possible signatures of axions—hypothetical 'ghost particles' theorized for decades and prime candidates for dark matter.
Neutron stars form when the core of a massive star collapses under gravity at the end of its life cycle. These ultra-dense objects, just a few kilometers across, pack densities up to a billion tons per cubic centimeter, made almost entirely of neutrons packed tightly together.
A group known as 'The Magnificent Seven' neutron stars has puzzled scientists. Current models predict they should emit ultraviolet light and low-energy X-rays. Yet observations revealed unexpected high-energy X-rays that defy explanation.
In a compelling new study, researchers propose these signals arise from axions. With decades of expertise in particle astrophysics, our analysis draws on precise observations to explore this frontier.
Axions were first proposed in 1977 to resolve the strong CP problem—a key puzzle in quantum chromodynamics explaining why neutrons show no electric dipole moment.
More recently, axions emerged as leading dark matter candidates, potentially comprising 26.8% of the Universe's mass-energy—invisible matter that neither emits, absorbs, nor reflects light.
Detecting these ghostly particles is challenging, but theory suggests they interact weakly with electromagnetic fields around neutron stars. Produced in vast numbers near the core, axions could convert to high-energy photons in the star's magnetic field, producing the observed X-rays.
As lead author Raymond Co from the University of Minnesota clarifies: "We're not claiming axion discovery yet. We're proposing that the excess high-energy X-ray photons around these stars could stem from axions—an exciting possibility aligned with our models."
Even if not axions, these X-ray excesses challenge the Standard Model, hinting at undiscovered physics. The research, grounded in rigorous data analysis, underscores our commitment to empirical validation.
Next steps include NASA's NuSTAR telescope for broader wavelength studies of The Magnificent Seven. Magnetized white dwarfs, with strong fields but no expected high-energy X-rays, offer additional testing grounds.
Details appear in Physical Review Letters.
