A team of astronomers has made the astonishing discovery of a barrier in the Milky Way.
A team of researchers from the Chinese Academy of Sciences in Nanjing has investigated a map of radioactive gamma rays – the highest energy form in the universe, which can be created when high-speed particles called cosmic rays collide. Ordinary matter – blasting in and around the center of our galaxy.
The map revealed that something near the galactic center appears to be accelerating particles to dizzying speeds – very close to the speed of light – and creating an abundance of cosmic rays and gamma rays outside the galactic center. However, even when the galactic center is “blowing” a continuous storm of high-energy radiation into space, something near the heart of the Milky Way prevents much of the cosmic rays from entering from other parts of the universe.
The researchers describe the effect as an invisible “barrier” that wraps around the galactic center and keeps the intensity of cosmic rays there well below the baseline level seen throughout our galaxy. In other words, cosmic rays can come out of the center of the galaxy, but they find it difficult to reach them.
The monster in the middle
The center of our galaxy is located about 26,000 light-years from Earth in the constellation Sagittarius. It’s a dense, dusty place, housing more than a million stars per light-year as the entire Solar System – all wrapped around 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 galactic center, is accelerating protons and electrons to near the speed of light, creating cosmic rays that shoot throughout our galaxy and beyond into intergalactic space. These rays propagate through our galaxy’s magnetic fields, creating an ocean of high-energy particles that are nearly the same in density throughout the Milky Way. This is known as the “sea of cosmic rays”.
In their new study, the researchers compared the intensity of cosmic rays in this sea with the intensity of cosmic rays inside the galactic center. Cosmic rays can’t be seen directly, but scientists can find them in gamma-ray maps of space, which effectively show where cosmic rays collide with other types of matter.
Using data from the Large Fermi Telescope, the team confirmed that something in the galactic center is indeed acting as a giant particle accelerator, spewing cosmic rays into the galaxy. Among those suspicious of causing this is “Arc A,” where black holes could theoretically shoot certain particles into space even when they gobble up everything else around them, Live Science previously reported, or even strong stellar winds from many jammed stars. At the center of the galaxy.
But the map also revealed a mysterious “barrier,” a visible point where the intensity of cosmic rays drops dramatically at the edge of the galactic center. The researchers said it is difficult to pinpoint the source of this phenomenon, but it may involve a mixture of magnetic fields near the dense core of our galaxy.
For example, thick clouds of dust and gas near the galactic center might collapse in on themselves, compressing the magnetic fields there and creating a barrier against cosmic rays, or perhaps stellar winds from the myriad stars in the galactic center rush against a sea of cosmic rays. Just like the solar wind does.