DIAS scientist helps reveal the mysterious cosmic ray factories in the Milky Way

Professor Felix Aharonian from the Dublin Institute for Advanced Studies (DIAS) has played a key role in the discovery of a dozen sources of the highest energy cosmic rays in our Galaxy.

The findings, which are published in Nature today, provide an important new insight into the origin of Galactic cosmic rays. These cosmic-ray factories, one of which is located in the famous Crab Nebula, were detected by observations with the Large High-Altitude Air Shower Observatory (LHAASO) in China.

Professor Felix Aharonian is Senior Scientific Advisor to the LHAASO collaboration and a co-author of the report in Nature.  Commenting on their findings, Professor Aharonian said: “Cosmic rays are charged particles that move at nearly the speed of light, with an energy spectrum that goes beyond one quadrillion electronvolts (1 petaelectronvolt, PeV.)

The search for powerful cosmic accelerators capable of reaching the PeV range – called PeVatrons – can be challenging because the trajectory of the charged cosmic rays is altered by interstellar magnetic fields. However, cosmic rays can produce gamma rays (y-rays) inside or in the vicinity of their accelerators, so searching for high-energy ?-rays can uncover the location of PeVatrons.”

Because of the enhanced technology, the LHAASO successfully detected 12 ultrahigh-energy sources of ?-rays of energies extending up to 1.4 PeV demonstrating the existence of PeVatrons within the Milky Way.

Professor Aharonian continued, “Over several decades, supernova remnants – relics of exploding stars – have been considered as prime candidate sites for the acceleration of high-energy cosmic rays. However, the sources detected by LHAASO seem to be associated with other types of celestial objects.

The precise location of most of these extreme accelerators remains unclear, but we expect to identify further sources when construction on LHAASO is complete, helping us to learn more about the matter and energy content and transport in the Universe.

“This is the first unambiguous and unbiased detection of PeVatrons, perfectly designed by Nature cosmic-ray factories – incredibly efficient machines accelerating particles at a rate close to the absolute theoretical margin determined by the laws of physics. This discovery shows that clusters of young, massive stars should be considered as a serious alternative or addition to supernova remnants as the main contributors to the Galactic Cosmic Rays.”

Prof. Aharonian believes that the results reported in the Nature article reveal only the tip of the iceberg: “In the coming years, we anticipate breakthrough discoveries by LHAASO that could dramatically change the current concepts about the most energetic and extreme phenomena in the non-thermal Universe.”

Dr Jonathan Mackey of DIAS, who works in computational astrophysics, especially related to massive stars and supernovae added: “Young star clusters are spectacular and energetic objects, containing the most massive and luminous stars in the Galaxy.

Powerful stellar winds and radiation from these young stars can rival the explosive energy of supernova explosions associated with stellar death, and it is exciting to see new evidence that these young stars could be producing the highest energy Galactic Cosmic Rays.”

For more information, the findings of the report can be read here.