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For the first time, scientists have spotted how a solar storm twists the stream of ultra-high-energy particles, turning them into a remote probe for magnetic fields.
Abstract
Large-scale anisotropy of cosmic rays at teraelectronvolt energies had not previously shown temporal variability. LHAASO data for the first time recorded transient anisotropy in ion fluxes. Analysis of hourly excess/deficit intensity maps revealed a gradient characterizing the direction and magnitude of the anisotropy. On November 4, 2021, over a few hours, the significance of the enhancement exceeded 5σ in four energy bands (median values 0.7–3.1 TeV). The gradient follows an E^{-0.5} dependence; at ≤1 TeV it corresponds to a dipole anisotropy of at least 1% (or a weaker higher-order component). This opens a new way to study interplanetary magnetic structures using wide-angle detectors, complementing direct plasma measurements.
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Cosmic rays are like a downpour pelting from all sides. But when the wind blows, the droplets change direction. In the same way, a solar storm—a cloud of magnetized gas from the Sun—bends the paths of these particles that normally rain down on Earth evenly.
Cosmic rays are invisible messengers from distant galaxies. They are mostly atomic nuclei accelerated by explosions of supernovae or other cosmic catastrophes.
On November 4, 2021, such a storm swept over our planet. The LHAASO observatory in China detected a temporary ‘warp’ in the stream of particles with energies trillions of times higher than visible light. And the higher the energy, the weaker the particles responded to the magnetic hurricane—a simple relationship akin to a power law. These wanderers travel for millions of years to reach us, yet are deflected by a storm in just a few hours. Now, just as ripples on puddles tell of the wind, astronomers reconstruct the picture of invisible magnetic fields in space from the bending of these streams.
🎯 Cosmic rays may travel for millions of years before hitting our atmosphere, but a solar storm can deflect them in just a few hours.
🎬 In his novel 'Solar Storm', Arthur C. Clarke depicted a catastrophic flare; real storms are less menacing, but they still spring surprises like this discovery.
E^\gamma
E — the particle's energy, γ — the exponent, in this case about −0.5
