Cosmic rays represent the most energetic particles discovered in nature, surpassing the energy levels achieved by even the most sophisticated accelerators on Earth. These particles are believed to originate from some of the universe's most tumultuous phenomena, such as supernova explosions, black hole jets, and pulsars.
The DAMPE space telescope, launched in December 2015, was specifically engineered to delve into the mysteries of cosmic rays while exploring potential links to dark matter. This mission has seen significant contributions from the astrophysics team at the Department of Nuclear and Particle Physics (DPNC) at the University of Geneva (UNIGE).
By analyzing the meticulously collected data from DAMPE, researchers have identified a universal trend in the energy spectra of primary cosmic ray nuclei, which range from lightweight protons to heavier iron nuclei.
According to Andrii Tykhonov, an associate professor at DPNC and co-author of the study, "Cosmic rays consist mainly of protons, but also include helium, carbon, oxygen, and iron nuclei." These particles are classified based on their energy levels: low (up to a few billion electron-volts), intermediate (from a few billion to several hundred billion electron-volts), and high (beyond 1,000 billion electron-volts).
Uncovering a Universal Cosmic Ray Phenomenon
The research revealed that, for each type of nucleus analyzed, the number of particles declines significantly after reaching a specific threshold, a phenomenon termed "spectral softening."
While it is typical for higher-energy cosmic rays to be less abundant as energy increases, DAMPE's findings indicated a steeper decline once a rigidity of approximately 15 TV (teraelectron-volts) is surpassed. Rigidity refers to the extent to which a particle's trajectory resists alteration by magnetic fields.
This consistent behavior across various particle types lends substantial support to theories suggesting that cosmic ray acceleration and their journey through space are governed by rigidity. The data effectively dismisses competing theories based on energy per nucleon, achieving a confidence level of 99.999% against those alternative models.
Innovative Techniques Propel Discovery
The Geneva team played a pivotal role in this groundbreaking research, employing advanced artificial intelligence techniques to reconstruct particle events detected by the telescope. They also made crucial measurements related to proton and helium fluxes and contributed to the analysis of carbon nuclei data.
Moreover, the Geneva group was instrumental in developing the Silicon-Tungsten Tracker (STK), a key instrument of DAMPE, which is vital for accurately tracing particle trajectories and determining the electrical charge of incoming cosmic rays.
This discovery marks a significant leap in our understanding of cosmic ray formation and their traversal through the galaxy. The new insights refine existing models of particle acceleration in astrophysical environments and enhance our comprehension of how high-energy particles navigate interstellar space, paving the way for future explorations in astrophysics.