A telescope array experiment has detected an extremely high-energy cosmic ray for the first time, which casts doubt on its origin because it points to the void of the universe and challenges current theories of the origin of cosmic rays and high-energy physics. Researchers involved in a telescope array experiment announced the detection of a cosmic ray of extraordinary energy.

Illustration of high-energy cosmic ray "Amaterasu particles" observed by the Telescope Array Experiment's surface detector array. Source: Osaka Metropolitan University/L-INSIGHT, Kyoto University/Takeshige Ryunosuke

This particle originates from outside the Milky Way and has an astonishing energy of more than 240 angstroms of electron volts (EeV). Despite this significant discovery, its exact origin remains elusive, as its direction of arrival does not point to any known astronomical entity.

Cosmic rays are subatomic charged particles coming from space, of which ultra-high-energy cosmic rays (UHECRs) are a rare and unusually powerful type. The energy of these ultra-high-energy cosmic rays exceeds 1EeV, which is approximately one million times the energy of human-made particle accelerators. They are thought to originate from the most energetic phenomena in the universe, such as those involving black holes, gamma-ray bursts and active galactic nuclei. However, their exact physics and acceleration mechanisms are still not fully understood. The frequency of these high-energy cosmic rays is so low—estimated at less than one particle per square kilometer every hundred years—that their detection is rare and requires instruments with huge collection areas.

Artist's astronomical map of ultra-high-energy cosmic rays, contrasted with weaker cosmic rays affected by electromagnetic fields, to illustrate extremely energetic phenomena. Source: Osaka Metropolitan University/Kyoto University/Takeshige Ryunosuke

Unique discovery of telescope array

On May 27, 2021, the "Telescope Array" (TA) experiment, a large-scale surface detector array located in Utah with an effective detection area of ​​700 square kilometers, successfully detected an ultra-high-frequency electromagnetic pulse with an energy of approximately 244EeV, which is of epoch-making significance.

The researchers note that given the particle's extremely high energy, it should be deflected only relatively slightly by the foreground magnetic field, and therefore its arrival direction should be more closely related to its source. However, the results show that its arrival direction does not reveal an obvious source galaxy, nor any other known objects thought to be potential sources of UHECR.

Instead, its arrival direction points to a hole in the large-scale structure of the universe - a region with very few galaxies. Scientists believe this may indicate a much larger magnetic deflection than predicted by models of the Milky Way's magnetic field, an unknown source in the extragalactic neighborhood, or an incomplete understanding of the associated high-energy particle physics.

References:

DOI:10.1126/science.abo5095

Compiled source:

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