Scientists have described this effect as an invisible "barrier" that wraps around the galactic center and keeps the density of cosmic rays there significantly lower than the baseline observed throughout the rest of our galaxy. In other words: cosmic rays can escape from the center of the Galaxy, but it is difficult for them to get inside.
For this study, a team of scientists from the Nanjing Academy of Sciences examined a map of the highest energy radioactive gamma rays in the universe that can occur when extremely high-speed particles called cosmic rays slam into ordinary matter, creating an explosion at the center of our galaxy and around it.
The map showed that something near the center of the galaxy is accelerating particles to incredible speeds - very close to the speed of light - and creating many cosmic rays and gamma rays just outside the galactic center. However, while the center of the galaxy is emitting a constant amount of high-energy radiation into space, something near the core of the Milky Way is preventing much of the cosmic rays from other parts of the universe from penetrating, as reported by the journal Nature Communications.
How this cosmic barrier works and why it exists remains a mystery.
The center of our Galaxy is located approximately 26,000 light-years away from the constellation Sagittarius ARS. It is a dense place with 1 million times more stars per light-year than the entire solar system - all surrounded by a supermassive black hole, about 4 million times the mass of the sun.
Scientists have long suspected that this black hole, called Sagittarius A *, or perhaps some other object in the center of the Galaxy, accelerates protons and electrons to near light speed, creating cosmic rays that spread throughout our galaxy and further into intergalactic space. These rays travel through the magnetic fields of our galaxy, creating an ocean of high-energy particles, roughly uniform in density throughout the Milky Way. This stable mixture of particles is called the sea of cosmic rays.
In their new study, scientists have compared the density of cosmic rays in this sea with the density of cosmic rays in the center of the Galaxy. Cosmic rays cannot be seen directly, but scientists can find them on gamma maps of the cosmos, which effectively show where cosmic rays collide with other types of matter.