Chinese scientists identify Milky Way origin of ultra-high energy cosmic rays

The existence of the bubble-like structure, which is about 10 million times the size of our solar system, suggests that, in contrast to previous theories about its origin, there is no way that ultra-high-energy gamma rays could be transported within the Milky Way. This could explain why this occurred, the researchers said.

“This is the first hypercosmic ray accelerator confirmed to date,” correspondent Cao Zhen, a professor at the Institute of High Energy Physics at the Chinese Academy of Sciences, told state-run Xinhua news agency.

Cosmic rays are charged particles that travel through space at nearly the speed of light. Although they were discovered more than 100 years ago, scientists still don’t know how the rays that reach Earth are formed or where they originate.

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Previous energy spectra of cosmic rays have shown an inflection point around the 1 petaelectronvolt (PeV) energy level. This is called a “knee” because of the shape of the graph.

Cosmic rays with energies below 1 PeV are thought to originate within the Milky Way galaxy, while cosmic rays with energies above this point are thought to originate from outside the galaxy, Cao told Sichuan News Network. told.

However, in 2020, Raaso discovered ultra-high-energy photons produced by cosmic rays with energies greater than 1 PeV originating from the constellation Cygnus. The latest paper details how these rays were formed.

The researchers found that bubble-like structures in the star-forming region of the constellation, called Cygnus X, contain photons larger than 1 PeV, including photons as high as 2.5 PeV.

The research team identified a huge star cluster called Cygnus OB2 at the center of the bubble. This cluster contains many young, hot stars, some of which have surface temperatures exceeding 35,000 degrees Celsius. This may be a supercosmic ray accelerator.

According to the paper, the bubble’s structure and energy spectrum are “reasonably reproduced by assuming a particle accelerator within the nucleus.”

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Cosmic ray accelerators can inject cosmic rays with energies of 10 to 25 PeV into interstellar space, where they collide with interstellar gas to produce observation photons with energies of 1 PeV or more.

Cao told Sichuan News Network that the stars in the cluster have a radiation intensity that is “1 million to 1 million times that of the Sun.” Material blown off the star’s surface by radiation pressure creates high-velocity winds that collide with the interstellar medium to form particle accelerators.

“After the accelerator is formed, microscopic particles dominated by protons are accelerated to very high energies, which become the cosmic rays observed on Earth,” Cao said.

The researchers found that the gas surrounding the bubble structure correlates with the intensity of gamma rays produced by energetic particles being accelerated into interstellar space.

“There is a strong assumption that all cosmic ray sources in our galaxy have such cosmic ray bubbles or halos,” the researchers wrote in their paper.

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The researchers were able to observe the bubbles because the cosmic rays spread much slower than expected, one-hundredth of the speed previously thought, Cao told Sichuan News Network. .

“As the observation time increases, Raso is expected to detect more hypercosmic ray accelerators,” he said in a Xinhua report. Cao added that he hopes further discoveries will “solve a century-old mystery about the origin of cosmic rays.”

Elena Amato, an astrophysicist at Italy’s National Institute of Astrophysics, said the results “have very relevant implications for the description of cosmic ray transport within galaxies.”