A collaboration of scientists from IceCube, the world’s largest neutrino observatory located deep in Antarctica, has obtained, for the first time, strong evidence that the Milky Way is a source of high-energy neutrino emission. The discovery, published today in the journal Science, confirms theoretical predictions that were made more than 40 years ago, and opens the door to investigate the origin of galactic cosmic rays, streams of charged particles that move at speeds close to that of the light.
The research team has applied machine learning techniques to more than 10 years of data from the observatory to identify previously undetected neutrinos. This treatment has finally confirmed the detection of galactic neutrinos from the Milky Way disk: “No previous attempt has come close to a level of statistical significance,” says Francis Halzen, principal investigator at the IceCube observatory and co-author of the article. of Science.
“The existence of this long-sought signal paves the way to the future of particle astrophysics in our Galaxy,” says Luigi Antonio Fusco, Professor of Particle Astrophysics at the University of Salerno, in Italy, in an analysis of the finding also published. Today in Science. “Observing neutrinos from the Galaxy tells us a lot about what cosmic rays do when they move through the Milky Way,” the expert, who has not participated in the research, develops in an email to La Vanguardia.
Neutrinos, extremely light particles with no electrical charge, are generated in the Universe when cosmic rays interact with the interstellar medium, that is, with the clouds of gas and dust found between the stars. In these same processes, very energetic electromagnetic radiation is also emitted, the so-called gamma rays.
Until now, various groups of scientists had been able to identify the radiation coming from the galactic disk but, beyond indications, they had not found any solid proof that neutrinos were also emitted. Since gamma rays can have other origins than cosmic rays, the finding presented today is essential to guarantee such an origin.
understand cosmic rays
Cosmic rays that reach Earth have been studied and measured for years. However, identifying their origin is a very difficult task, because they do not follow a straight line in their journey through the galaxy. Being charged particles, their trajectory is constantly deflected by the magnetic fields of stars and other celestial objects, making it impossible to follow their path.
Neutrinos, on the other hand, having no charge, move in a straight line and, furthermore, have the advantage that they practically do not interact with the interstellar medium, unlike radiation, which can be blocked by gas and dust. Therefore, the neutrinos that are created from cosmic rays and that leave in the direction of our planet will reach it and, if we are able to measure their trajectory, they will be able to indicate the point where they originated, revealing data about cosmic rays. initials.
The finding presented today in Science does not go into such detail, but it sets the first stone on this path. The members of the IceCube collaboration have not been able to precisely establish the origin of the detected neutrinos, although the most plausible interpretation of the data, according to the authors themselves, is that it is a diffuse emission. That is, that cosmic rays have interacted with matter while traveling through the galactic disk, far from where they originated.
One of the main goals of neutrino astronomy is to identify point sources of these particles. Finding them “would imply identifying individual sources of galactic cosmic rays, which is the ultimate goal of particle astrophysics,” says Fusco, who has been involved in the search for neutrinos for the past 10 years.
“Neutrinos are tracers of cosmic ray sources,” Halzen agrees. “Astronomers have observed very high-energy gamma ray sources that are potential sources of cosmic rays,” develops the researcher, whose objective is to confirm “some of them as cosmic ray sources by detecting the emission of neutrinos.”
However, these next steps are still some way off. “To identify point sources we need better angular precision […] than what we get with IceCube”, reasons Fusco, from the University of Salerna. “This is the goal of the next generation of neutrino telescopes like KM3NeT, which is being built in the Mediterranean Sea,” concludes the expert.
“The IceCube data suggest that there is a wealth of sources to be discovered with a more sensitive instrument,” agrees the principal investigator of the observatory.
