June 30 () –
Scientists have revealed a singularly different picture of the Milky Way by determining the galactic origin of thousands of neutrinos, invisible “ghost particles” that exist in large numbers but that normally they cross the Earth without being detected, according to what they publish in the magazine ‘Science’.
The neutrino-based image of the Milky Way is the first of its kind and is a galactic portrait made with particles of matter rather than electromagnetic energy.
From visible starlight to radio waves, the Milky Way has been observed for a long time through the different frequencies of electromagnetic radiation it emits. Now the breakthrough has been made possible thanks to the collaboration of researchers using the IceCube Neutrino Observatory at the NSF’s Amundsen-Scott South Pole Station in Antarctica.
The massive observatory detects subtle high-energy neutrino signals from space using thousands of networked sensors buried deep within a cubic kilometer of pristine, transparent ice.
“TO At this point in human history, we are the first to see our galaxy in a way other than light.“, explains Naoko Kurahashi Neilson, a physicist at Drexel University, referring to the moment when she and two doctoral students, Steve Sclafani, from Drexel (United States), and Mirco Hünnefeld, from the Technical University of Dortmund (Germany), first examined the image.
Kurahashi Neilson proposed the innovative computational analysis used to generate the image and received funding to carry out his idea through a grant from the NSF’s Faculty Early Career Development program.
“As is often the case, technological advances make major scientific breakthroughs possible. says Denise Caldwell, director of the NSF’s Division of Physics. The possibilities offered by the highly sensitive IceCube detector, together with new data analysis tools, have given us a completely new view of our galaxy, which until now has only been hinted at.”
“As these capabilities continue to be refined, we can expect to see this image emerge with ever higher resolution, potentially revealing hidden features of our galaxy never before seen by humanity,” he adds.
“What is intriguing is that, unlike light of any wavelength, in neutrinos the universe eclipses nearby sources in our own galaxy,” says Francis Halzen, a physicist at the University of Wisconsin-Madison and principal investigator for IceCube.
Beyond the challenge of detecting the elusive neutrinos and distinguishing them from other types of interstellar particles is the even more ambitious goal of determining their provenance. When neutrinos interact with ice under IceCube, those rare encounters produce faint patterns of light that IceCube can detect.
Some light patterns are highly directional and clearly point to a specific area of the sky, allowing researchers to determine the source of the neutrinos. These interactions were the basis for the discovery in 2022 of neutrinos from another galaxy 47 million light-years away.
Other interactions are much less directional and produce “cascading balls of light” on transparent ice, explains Kurahashi Neilson. Their IceCube Collaboration colleagues Sclafani and Hünnefeld developed a machine learning algorithm that compared the relative position, size, and energy of more than 60,000 neutrino-generated light cascades recorded by IceCube over 10 years.
The three researchers spent more than two years meticulously testing and verifying their algorithm with artificial data that simulated neutrino detections.
When they finally fed the actual data provided by IceCube into the algorithm, the result was an image showing bright spots corresponding to places in the Milky Way suspected of emitting neutrinos. These were places where the observed gamma rays were thought to be by-products of collisions between cosmic rays and interstellar gas, which theoretically should also produce neutrinos.
“Now a homologous neutrino has been measured, thus confirming what we know about our galaxy and the sources of cosmic rays,” stresses Sclafani.
Over many decades, scientists have revealed countless astronomical discoveries by expanding the methods used to observe the universe. Once revolutionary advances such as radio astronomy and infrared astronomy have been joined by a new class of observing techniques that use phenomena such as gravitational waves and now neutrinos.
Kurahashi Neilson says the neutrino-based image of the Milky Way is another step in that lineage of discovery. He predicts that neutrino astronomy will be perfected like the methods that came before it, until it too can reveal hitherto unknown aspects of the universe.
