According to a recent study, the core of the Milky Way may be considerably stranger than scientists 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 near the galactic core appears to be accelerating particles to incredible speeds — very close to the speed of light — and producing an abundance of cosmic rays and gamma-rays just outside the galactic centre. Despite the fact that the galactic centre is constantly releasing a torrent of high-energy radiation into space, something in the Milky Way’s core stops a major fraction of cosmic rays from other areas of the cosmos from entering, the team reported Nov. 9 in the journal Nature Communications.
The effect 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.
Monster in the Center
Our galaxy’s centre is around 26,000 light-years 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 hypothesised that this black hole, known as Sagittarius A*, or another object at the galactic centre, 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 centre in their latest study. Scientists can discover cosmic rays in gamma-ray maps of space, which effectively depict where cosmic rays have clashed with other types of matter.
The scientists established that something in the galactic centre is definitely serving as a huge particle accelerator, spewing cosmic rays out into the galaxy using data from the Fermi Large Area Telescope. Sagittarius A*, as black holes might hypothetically spew certain particles into space while gobbling up everything else around them, Live Science previously reported; leftovers of ancient supernovas; or even intense stellar winds from the galactic center’s countless stars.
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.
The scientists proposed in their paper that massive clouds of dust and gas surrounding the galactic centre may 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 happening in the strange depths of our galaxy.