At an altitude of 13,000 feet (4000 meters), on the Sierra Negra volcano in Mexico, researchers from the High-Altitude Water Cherenkov (HAWC) observatory are tracking extreme phenomena. At the heart of the Milky Way, gamma rays of unprecedented power have been detected.
These gamma rays, exceeding 100 teraelectronvolts, come from a specific region: the galactic center. For the first time, an international team has traced them back to their origin, thereby revealing the presence of a PeVatron, a still mysterious source of extreme energy.
According to scientists, this observation constitutes an unprecedented breakthrough in the study of the most violent physical processes in the Universe. It helps to understand how certain gamma rays reach dizzying energies and the phenomena that lie behind them.
The PeVatron, the source of these ultra-energetic gamma rays, remains largely misunderstood. Researchers suggest that this entity could be associated with the hostile environments surrounding the Milky Way's supermassive black hole, a location largely inaccessible to conventional observations.
The central region of the Milky Way is known for its intense activity, where neutron stars and white dwarfs mix. Surrounded by clouds of searing gas, this area emits energy that is difficult to observe directly. However, gamma rays can penetrate this darkness, as they travel through dense gas.
The particles accelerated by the PeVatron reach energies of the order of 1 petaelectronvolt (PeV), well beyond the capabilities of human technology. These particles interact with the surrounding gases, producing the gamma rays that HAWC can observe. This phenomenon highlights a rarely seen power in the Milky Way.
To capture these rays, HAWC uses giant water tanks. When a high-energy particle travels through the water at a speed greater than that of light in this medium, it emits a blue glow, called Cherenkov radiation, similar to a sonic "boom" but for light.
Results of the analysis of the galactic center.
Credit: The Astrophysical Journal Letters (2024)
The analysis of this data allows tracing the origin of the detected particles and understanding the energy involved in these phenomena. HAWC, which extends the Milagro project's experiment in New Mexico, is located further south.
Researchers plan to expand their observations at a new observatory in Chile, the Southern Wide-field Gamma-ray Observatory. By broadening their observational field, they hope to unravel the mysteries of PeVatrons and the extreme phenomena at the heart of our galaxy.
What is a PeVatron?
The PeVatron is a source of extremely energetic gamma rays, capable of accelerating particles to energies close to a petaelectronvolt (PeV), or one quadrillion electronvolts. This term combines "PeV" for extreme energy and "tron" for particle acceleration.
The mystery of PeVatrons intrigues researchers, as it suggests violent physical processes, like those observed in the galactic center, around supermassive black holes or star explosions (supernovae). This type of source could also be linked to collisions of stellar cores or mergers of neutron stars.
PeVatrons are essential for understanding how cosmic particles are accelerated to speeds close to that of light. They help explain the propagation of gamma rays in our galaxy and are indicators of rare and intense energetic phenomena in the Universe.
The study of PeVatrons, facilitated by observatories like HAWC, deepens our understanding of the interactions between cosmic rays and the interstellar medium, shedding new light on extreme galactic environments.