The new map developed by Chinese scientists of the Milky Way Galaxy turns the tables on theories of cosmic radiation

The results “will give new insight into the propagation and interaction processes and the origin of the highest energy cosmic rays in our galaxy,” said Kazumasa Kawata, of the University of Tokyo’s Cosmic Ray Research Institute in Kashiwa, Japan.


A “massive” black hole at the center of our galaxy is seen for the first time

A “massive” black hole at the center of our galaxy is seen for the first time

Since Austrian physicist Viktor Hess discovered cosmic rays in 1912, scientists have built detectors in… space And on Earth to search for these mysterious and powerful particles from outer space, Kawata wrote in the journal Physics.

The highest energy cosmic ray ever detected carries over a quintillion electron volts – equivalent to the kinetic energy of a baseball moving at 100 mph (160 km/h), or millions of times more energy than the particles created in the largest particle. . Collider on Earth.

Today, scientists still do not have a clear answer about the actual source of cosmic rays. Since they are mainly composed of protons, their electrically charged nature means that they do not move in a straight line, and are instead deflected by the magnetic fields of the universe. This means that basic information about their birthplace will be lost when they arrive on Earth, Kawata wrote.

However, if cosmic rays hit gas clouds on their way out, they generate electrically neutral gamma-ray light particles that are unaffected by magnetic fields. The energy of these light particles is about one-tenth the energy of their parent particles Cosmic rays.

Therefore, by studying the number, distribution and energy spectrum of these gamma rays, scientists can glimpse the origins of cosmic radiation.

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Due to the limited sensitivity of the detectors, previous observations of the gamma-ray haze in the Milky Way were performed with space telescopes at energies below a trillion electron volts.

When LHAASO was completed in 2021, it became the world’s largest and most sensitive observatory for detecting gamma rays and very high energies cosmic rays. A key component of LHAASO is called the Kilometer Square Array, or KM2A, which includes about 5,200 surface electromagnetic detectors and nearly 1,200 underground muon detectors.

The researchers first removed dozens of gamma-ray sources that are pointy — rather than diffuse — in the galaxy. They then made one of the most comprehensive and precise measurements of the gamma flare distribution over a wide energy range of 0.1-1 PeV and across a large area of ​​the galaxy, including the inner and outer galactic levels.

To their surprise, the number of scattered gamma rays measured by LHAASO is two to three times higher than expected cosmic ray collisions with interstellar gas.

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Also different from expectations, the energy spectrum of gamma emission can be expressed by a single power law without any discontinuity, contradicting the popular theory that very high-energy cosmic rays would be trapped by the galaxy’s magnetic fields for a long time. , anywhere between 10,000 and 10 million years ago, before they finally escaped from the pool.

“The discrepancy suggests that additional sources of gamma rays are hidden in our galaxy, or that cosmic ray densities change depending on the location in our galaxy,” said Kawata, who worked on a Sino-Japanese collaboration project called Tibet AS-gamma. Experience for many years.

Kawata noted that it will be important for the world’s major cosmic ray detectors to confirm each other’s observational results in the future.

For example, a recent map of the Milky Way released by the US-led IceCube Collaboration, which studies cosmic neutrinos thousands of meters below the South Pole, has provided strong evidence of interactions between cosmic rays and interstellar gas.

By putting these pieces together, scientists should be able to gain more knowledge about the mysterious origins of cosmic radiation, he said.

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