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Astronomers have discovered a massive 'barrier' separating the Milky Way's core from the cosmic ray sea.

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Something is preventing the universe's fastest-moving particles from entering our galaxy's core. According to a recent study, the heart of the Milky Way may be far weirder than scientists previously assumed.


A team of researchers from the Chinese Academy of Sciences in Nanjing investigated a map of radioactive gamma-rays — the highest-energy form of light in the universe, which can arise when extremely fast particles known as cosmic rays collide with ordinary matter — blasting in and around the centre of our galaxy for the study.


The map revealed that something around the galactic core appears to be accelerating particles to mind-boggling speeds — extremely close to the speed of light — and producing a plethora of cosmic rays and gamma-rays just outside the galactic center. 


Even though the galactic center emits a constant storm of high-energy radiation into space, something near the Milky Way's core prevents a large portion of cosmic rays from other parts of the universe from entering, according to the team's report published Nov. 9 in the journal Nature Communications.


The impact was described by the researchers as an unseen "barrier" that wraps around the galactic centre and keeps the density of cosmic rays there much lower than the baseline level seen throughout our galaxy. 


In other words, cosmic rays can leave the galactic core but have a difficult time entering.


It's unclear how this cosmic barrier works or why it exists.


The monster in the center

The core of our galaxy is approximately 26,000 light-years away from Earth in the constellation Sagittarius. It's a crowded and dusty environment, with more than a million times as many stars per light-year as the entire solar system — all encircled by a supermassive black hole 4 million times the mass of the sun.


Scientists have long hypothesized that this black hole, known as Sagittarius A*, or another object at the galactic center, is speeding protons and electrons to near light speed, resulting in cosmic rays that travel throughout our galaxy and beyond. 


These rays propagate across our galaxy's magnetic fields, forming an ocean of high-energy particles that is nearly homogeneous in density over the whole Milky Way. The cosmic ray sea is the name given to this constant soup of particles.


The researchers matched the density of cosmic rays in this sea to the density of cosmic rays in the galactic center in their latest study. Cosmic rays cannot be seen directly, but they can be found on gamma-ray maps of space, which reveal where cosmic rays have clashed with other types of matter.


Using data from the Fermi Large Area Telescope, the team determined that something in the galactic core is serving as a massive particle accelerator, ejecting cosmic rays into the galaxy.


Sagittarius A*, as black holes could theoretically shoot certain particles into space while gobbling up everything else around them, Live Science previously reported; the remnants of ancient supernovas; or even strong stellar winds from the many stars crammed into the galactic center, are all possible culprits.


However, the map revealed the enigmatic "barrier," a visible area where the quantity of cosmic rays goes off dramatically at the galactic center's border. The source of this anomaly is more difficult to determine, according to the researchers, but it could entail a jumble of magnetic fields at our galaxy's dense core.


According to the team's report, massive clouds of dust and gas surrounding the galactic center could collapse on themselves, compressing the magnetic fields and producing a cosmic-ray-proof barrier. 


Perhaps stellar winds from the galactic core are pushing back against the cosmic ray sea in the same way that the solar wind does.


More investigation is needed to determine what is going on in the strange depths of our galaxy.


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