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Scientists are trying to resolve a mystery of a decade by determining the identity of the abnormal signals detected below the antarctic ice.
The strange radio waves emerged during a search for another unusual phenomenon: high energy cosmic particles called neutrinos. Arriving on the earth of the large range of the cosmos, neutrinos are often called “ghostly” because they are extremely volatile or vaporous, and can go through any kind of material without changing.
Over the past decade, researchers have conducted several experiences using large expanses of water and ice designed for Search for neutrinoswhich could shed light on mysterious cosmic rays, the most energetic particles of the universe. One of these projects was the antarctic impulsive transitional antenna of NASA, or Anita, which stole balloons bearing instruments above Antarctica between 2006 and 2016.
It was during this hunt that Anita picked up abnormal radio waves which did not seem to be neutrinos.
The signals came from under the horizon, suggesting that they had crossed thousands of kilometers of rock before reaching the detector. But the radio waves should have been absorbed by the rock. The Anita team thought that these abnormal signals could not be explained by the current understanding of particle physics.
Follow -up observations and analyzes with other instruments, including a recently led by the Pierre Auger observatory in Argentina, could not find the same signals. The results of the Pierre Auger collaboration were published in the journal Physical examination letters In March.
The origin of the abnormal signals remains clear, said the co-author of the Stephanie Wissel study, an associate professor of physics, astronomy and astrophysics at the Pennsylvania State University.
“Our new study indicates that such (signals) have not been seen by experience … like the Pierre Auger observatory,” said Wissel. “So that does not indicate that there is a new physics, but rather more information to add to the story.”
Larger and more sensitive detectors may be able to solve the mystery, or finally prove whether the abnormal signals were a stroke of luck, while continuing the search for enigmatic neutrinos and their sources, according to scientists.
The detection of neutrinos on earth allows researchers to trace them to their sources, which, according to scientists, are mainly cosmic rays which strike the atmosphere of our planet.
The most energetic particles of the universe, the cosmic rays are mainly composed of protons or atomic nuclei, and they are unleashed through the universe because everything that produces them is an accelerator of particles so powerful that it eclipses the capacities of the great collision of Hadrons. Neutrinos could help astronomers better understand the cosmic rays and what launches them through the cosmos.
But neutrinos are difficult to find because they have almost no mass and can pass through the most extreme environments, such as stars and whole galaxies, unchanged. However, they interact with water and ice.
Anita was designed to search for the highest energy neutrinos in the universe, to higher energies than that has not yet been detected, said Justin Vandenbroucke, an associate professor of physics at the University of Wisconsin, Madison. The radio antennas of the experience are looking for a short pulse of radio waves produced when a neutrino collides with an atom in the Antarctic ice, leading to a shower of low energy particles, he said.
During her flights, Anita found fountains of high -energy particles from ice, a kind of shower upside down with cosmic rays. The detector is also sensitive to ultra-vow cosmic rays that rain on earth and create a radio that acts like a beam of radio wave lamp.
When Anita looks at a cosmic ray, the pocket lamp beam is really an explosion of radio waves of a million seconds which can be mapped like a wave to show how it is reflected on the ice.
Twice in their data from Anita flights, the original team of the experience has identified signals through ice at a much clearer angle than ever planned by all models, which makes it impossible to trace signals at their original sources.
“The radio waves that we detected almost a decade ago were at really steep angles, like 30 degrees below the surface of the ice,” said Wissel.
Neutrinos can travel through a lot of matter, but not through Earth, said Vandenbroucke.
“They should arrive slightly below the horizon, where there is not much soil to absorb,” he wrote in an email. “Anita abnormal events are intriguing because they seem to come well below the horizon, so neutrinos should travel through a large part of the earth. This is not possible according to the standard model of particle physics.”
The Pierre Auger collaboration, which includes hundreds of scientists from around the world, has analyzed more than a decade of data to try to understand the abnormal signals detected by Anita.
The team also used their observatory to try to find the same signals. The Auger’s Observatory is a hybrid detector that uses two methods to find and study cosmic rays. A method is based on the search for high energy particles because they interact with water in the tanks on the surface of the earth, and the others follow potential interactions with the ultraviolet light raised in the atmosphere of our planet.
“The Auger observatory uses a very different technique for observing the air showers of ultra-souci energy cosmic rays, using the secondary glow of the charged particles while they cross the atmosphere to determine the direction of the cosmic ray that initiated it,” said Peter Gorham, professor of physics at the University of Hawaii in Mānoa. “Using computer simulations of what such a particle shower would look like if it had behaved like Anita abnormal events, they are able to generate a kind of model for similar events, then search for their data to see if something as it appears.”
Gorham, who was not involved in the new research, designed the Anita experience and carried out other research to better understand the abnormal signals.
While the Auger Observatory was designed to measure the downward particles produced in the atmosphere by ultra-energy cosmic rays, the team has redesigned their data analysis to search for upwards, said Vandenbroucke. Vandenbroucke did not work on the new study, but he evaluated it by peers before the publication.
“Auger has a huge collection area for such events, larger than Anita,” he said. “If the abnormal events Anita are produced by a particle traveling across the earth and then producing upward showers, the auger should have detected a lot, and this is not the case.”
A separate follow -up study Using the Icecube experience, which has sensors integrated in the depths of Antarctic ice, also looked for abnormal signals.
“Because the Icecube is very sensitive, if the abnormal events Anita were neutrinos, we would have detected them,” wrote Vandenbroucke, which served as a colead of the working group on the sources of Neutrinos Icecube between 2019 and 2022.
“This is an interesting problem because we still have no explanation for what these anomalies are, but what we know is that they probably do not represent neutrinos,” said Wissel.
Curiously, another type of neutrinos, called a tau neutrino, is a hypothesis that certain scientists have presented as the cause of abnormal signals.
Tau neutrinos can regenerate. When they break down to high energies, they produce another tau neutrino, as well as a particle called Tau Lepton – similar to an electron, but much heavier.
But what makes the scenario of neutrinos tau very unlikely is the slope of the signal angle, said Wissel.
“You expect all these tau neutrinos to be very, very close to the horizon, like perhaps one to five degrees under the horizon,” said Wissel. “These are 30 degrees under the horizon. There are simply too much equipment. They would really lose a little energy and would not be detectable.”
In the end, Gorham and the other scientists have no idea of the origin of Anita abnormal events. Until now, no interpretation corresponds to the signals, which makes it possible to bring the scientists back to try to resolve the mystery. The answer can however be in sight.
Wissel also works on a new detector, the payload for ultra-high or Pueo energy observations, which will fly over Antarctic for a month from December. Larger and 10 times more sensitive than Anita, Pueo could reveal more information on what causes the abnormal signals detected by Anita, Wissel said.
“Right now, this is one of these long -standing mysteries,” said Wissel. “I am delighted that when we pilot Pueo, we will have better sensitivity. In principle, we should be able to better understand these anomalies which will greatly contribute to understanding our history and ultimately detecting neutrinos in the future. ”
Gorham said Pueo, an acronym that refers to the Hawaiian owl, should have the sensitivity to capture many abnormal signals and help scientists find an answer.
“Sometimes just go back to the drawing board and really understand what these things are,” said Wissel. “The most likely scenario is that it is banal physique that can be explained, but we somehow strikes all doors to try to understand what it is.”