Something is keeping cosmic rays out of the Milky Way’s center

A 'barrier' separating the cosmic ray sea from the galactic center.


The Milky Way’s center is dense and dusty. There is a supermassive black hole called Sagittarius A* at the middle of our Milky Way galaxy, which is about 4 million times the sun’s mass.

Scientists have long believed that the black hole or any other object at the galactic center accelerates protons and electrons to near light speed, creating cosmic rays. These cosmic rays pass out through the magnetic fields of the galaxy.

Thereby it creates an ocean of high-energy particles that’s roughly uniform in density throughout the entire Milky Way. This steady soup of particles is called the cosmic ray sea.

Recently, a team of scientists from the Chinese Academy of Sciences in Nanjing used data from the Fermi Gamma-ray Space Telescope and investigated a map of radioactive gamma-rays blasting in and around the center of our galaxy. The map revealed that something near the galactic center accelerates the particles at a similar speed of light and creates an abundance of cosmic rays and gamma rays just outside the galactic center.

However, there is something near the Milky Way’s core that obstructs a large portion of cosmic rays from other parts of the universe from entering.

This effect has been termed as ‘barrier,’ wrapped around the galactic center. It keeps the density of cosmic rays there significantly lower than the baseline level seen throughout the rest of our galaxy.

Xiaoyuan Huang at the Chinese Academy of Sciences said, “If there is no barrier, the cosmic ray sea component should also be present in the CMZ region. However, the data indicate that it is just the opposite and a barrier must be present.”

Scientists noted“The source of this phenomenon is harder to pinpoint, but it may involve the jumble of magnetic fields near our galaxy’s dense core.”

Further research is required to figure out precisely what is happening in the mysterious depths of our galaxy.

Journal Reference:

  1. Huang, X., Yuan, Q. & Fan, YZ. A GeV-TeV particle component and the barrier of the cosmic-ray sea in the Central Molecular Zone. Nat Commun 12, 6169 (2021). DOI: 10.1038/s41467-021-26436-z
Latest Updates