A lone, high-energy neutrino struck Earth on September 22 last year. It came from a very distant galaxy spiraling with a supermassive black hole. This single finding is historical since it manages to answer a cosmological enigma that has intrigued the scientific community more than 100 years ago: where cosmic rays come from or the most powerful particle emissions known. The research was published in Nature.
This happens because the phantom particle (this is also known as neutrinos) that barely interacts with other materials, has left enough clues to understand where they really come from. For 4 billion years, this neutrino traveled through space without anything stopping it. He passed stars, pieces of rock and other galaxies.
It could have even passed through them since neutrinos often navigate through matter without leaving any clue, that’s why ghosts. So, all the time it took for life to emerge on Earth, for bacteria, fungi, plants and animals to emerge, and for a species of these animals (us) to know of their existence, this neutrino traveled without disturbances.
Finally, the neutrino crashed into an atom in a block of ice in Antarctica, firing another high-energy particle called a muon into the IceCube Neutrino Observatory, a particle detector under the Antarctic ice, and disappeared forever.
It happens all the time, but this was special
A high-energy neutrino stream from the depths of the cosmos hits the Earth all the time. Although this was special because the scientists were ready for it. For years, they refined their instruments to detect it, they understood from what part it could come, and they pointed their telescopes from all over the world to that part of the sky.
It was not the first time it was tried, but it worked. The Fermi Gamma-ray Space Telescope and dozens of additional observatories around the world picked up the weak signal from the neutrino source called blazar by its glow of electromagnetic energy thrown toward the Earth.
The researchers concluded that there is a blazar in deep space, part of the family of brightest objects in the universe (galaxies with supermassive black holes shooting energy beams towards the earth). And this blazar accelerates neutrinos to enormous energies to send them towards our planet.
The megaproject for detection
The finding is possible thanks to IceCube, according to one of the researchers who authored the work, Derek Fox, an astrophysicist at Pennsylvania State University.
“Most neutrinos that collide with our bodies on a daily basis are formed in the atmosphere as a result of collisions between gases and other high-energy cosmic particles. These local neutrinos blot out the most sensitive instruments like mists.
In 2013, however, IceCube managed to see through that haze. It was able to filter the higher energy cosmic neutrinos and separate them from the radiation of their lower energy atmospheric cousins. This was the first great direct proof that neutrinos originated very far away.
The next important step, according to Regina Caputo, a scientist who led the Fermi telescope team that detected blazar in the neutrino path of this story, was to understand how neutrino information could be used to trap its origin.
Fox went there to carve. His team managed to detect cosmic neutrinos through IceCube in less than a minute (it used to take hours), something that allowed other observatories to be alerted just moments after interesting detection occurred.
IceCube was able to follow the path of the neutrino thanks to the muon emitted to reduce the piece of sky to observe, an estimated twice the full moon. Taking that information quickly allowed a select group of the world’s most sensitive telescopes to scan the space for clues of its origin.
When the neutrino called IceCube-170922 hit the detector, it did not seem anything special. IceCube made this type of detections once a month. Days passed when the telescopes searched for clues of origin and nothing happened.
But suddenly, Fermi researchers warned: the blazar was shining. The gamma-ray telescope had seen it and it emitted 8 times more gamma rays than usual, the brightest ever seen before. Fermi, then, confirmed that the gamma radiation came from the blazar and other less powerful telescopes could follow up to confirm, through the range of its possibilities, that the blazar is the possible origin of the neutrino.
Another gamma-ray observatory, MAGIC from the Canary Islands, Spain, helped confirm these observations on the blazar, called TXS 0506 + 056, as the origin of the neutrino. More observatories resulted in similar conclusions. It is, confirmed by many scientists, the first time that the origin of a cosmic neutrino is identified in consensus.
The idea that the blazars are involved in the emission of cosmic neutrinos has been popular for many years but has not gone beyond the field of speculation. The result shows that at least some neutrinos come from blazars, and are a first step in understanding what a new field in astronomy would be like.
Another detail that is not known is how the blazars produce neutrinos. And there are other types of neutrino sources that have not yet been detected.