In a groundbreaking discovery, researchers have identified the second-most powerful cosmic ray originating from outside our galaxy. Named the ‘Amaterasu’ particle after the Japanese sun goddess, the ultra-high-energy cosmic ray was observed in Utah, marking a significant milestone in cosmic exploration. The findings, published in the journal Science, have left scientists intrigued as the exact origin of this powerful particle remains shrouded in mystery.
The ‘Amaterasu’ particle, with an energy equivalent to “dropping a brick on one’s toe from waist’s height,” was measured at 2.4 x 10^20 electron Volts (eV) and was detected on May 27, 2021.This discovery is considered the most powerful cosmic ray detection since the enigmatic ‘Oh-My-God’ particle in 1991, which had baffled physicists at the time.
Cosmic rays, charged particles like protons or electrons traveling at nearly the speed of light, traverse the universe and may be remnants of celestial events breaking down matter to its subatomic constituents. The flight path of these charged particles resembles a ball in a pinball machine as they zigzag against electromagnetic fields through the cosmic microwave background.
John Matthews, a co-author of the study, remarked, “The particles are so high energy, they shouldn’t be affected by galactic and extra-galactic magnetic fields. You should be able to point to where they come from in the sky.” However, researchers are grappling with the mystery of the particle’s source, with no conventional explanation in sight.
The research, conducted at the Telescope Array at the University of Utah, echoes the historical significance of the ‘Oh-My-God’ particle discovery in 1991 during the ‘Fly’s Eye’ experiment. Like its predecessor, the ‘Amaterasu’ particle poses challenges to conventional astrophysical explanations, suggesting potential unknowns in particle physics.
Matthews highlighted the rarity of such phenomena, stating, “Things that people think of as energetic, like supernova, are nowhere near energetic enough for this. You need huge amounts of energy, really high magnetic fields to confine the particle while it gets accelerated.”
The composition analysis of the cosmic ray hints that the ‘Amaterasu’ particle is likely a proton due to its relatively unbent trajectory, distinguishing it from heavier particles like iron nuclei.
The researchers delved into particle physics theories, noting that a cosmic ray with energy beyond the Greisen-Zatsepin-Kuzmin (GZK) cutoff, such as ‘Amaterasu,’ is too powerful for the microwave background to distort its path. Yet, the mystery deepened when back-tracing the particle’s trajectory pointed to empty space, leaving scientists puzzled.
Study co-author John Belz, a professor at the University of Utah, remarked, “Maybe magnetic fields are stronger than we thought, but that disagrees with other observations that show they’re not strong enough to produce significant curvature at these ten-to-the-twentieth electron volt energies. It’s a real mystery.” The quest for understanding the origin of this powerful cosmic ray continues, unraveling new mysteries in the vastness of outer space.
