THE CENTER of the Milky Way may be more unusual than astronomers thought, according to a new study.
Something is preventing the fastest-moving particles in space from entering the center of our galaxy.
For this study, a team of researchers from the Chinese Academy of Sciences in Nanjing investigated a map of radioactive gamma rays – the largest energy form of light in the universe – that explode in or around the center of our galaxy.
The map revealed that something near the center of the galaxy accelerates particles to incredible speeds – almost to the speed of light – and creates an abundance of cosmic rays and gamma rays not far from the galactic center. However, although the galactic center is emitting a storm of high-energy radiation into space, something close to the core of the Milky Way prevents much of the cosmic rays from other parts of the universe from entering our galaxy, the team announced in the journal “Nature Communications”.
Researchers have described the effect as an invisible “shield” around the galactic center that keeps the density of cosmic rays significantly lower than the baseline level seen in the rest of our galaxy. In other words, cosmic rays can come out of the galactic center, but it is very difficult to enter it.
How this cosmic barrier works, or why it exists, remains a mystery.
A monster in the middle
The center of our galaxy is located about 26,000 light-years from Earth in the constellation Sagittarius. It is a dense and dusty place, containing more than a million times more stars per light year than the entire solar system – everything is wrapped around a supermassive black hole with about four million times the mass of the Sun.
Scientists have long suspected that this black hole, called Sagittarius A *, accelerates protons and electrons to a speed close to light, creating cosmic rays that propagate through our galaxy and further into intergalactic space. These rays propagate through the magnetic fields of our galaxy, creating an ocean of high-energy particles whose density is approximately uniform throughout the Milky Way. This stable particle soup is called a sea of cosmic rays.
In their new study, the researchers compared the density of cosmic rays in this sea with the density of cosmic rays within the galactic center. Cosmic rays cannot be seen directly, but scientists can find them in gamma-ray maps of the universe, which effectively show where cosmic rays collided with other types of matter.
Using data from Fermi’s large-area telescope, the team confirmed that something in the galactic center really acts as a giant particle accelerator, emitting cosmic rays into the galaxy. Possible culprits include Sagittarius A *, since black holes can theoretically throw out.
The map also revealed a mysterious “shield”, a clear point where the density of cosmic rays drops significantly on the edge of the galactic center. The source of this phenomenon is more difficult to determine, the researchers said, but it could involve the confusion of magnetic fields near the dense core of our galaxy.
For example, dense clouds of dust and gas near the galactic center could collapse, compressing the magnetic fields there and creating a shield resistant to cosmic rays, the team states in its work. Or maybe the stellar winds with countless stars in the galactic center are being pushed back towards the sea of cosmic rays, just as the solar wind does, writes Live Science.
Further research is needed to find out exactly what is happening in the bizarre depths of our galaxy.
Starry sky – Sputnik Serbia, 1920, 11/18/2021
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