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The Milky Way galaxy has always been studied using different types of light, from visible starlight to radio waves. However, scientists have now taken a unique approach by using invisible particles called neutrinos to create a new image of our galaxy. Neutrinos are ghost-like particles that usually pass through Earth without being noticed. By determining the origin of thousands of neutrinos, researchers have produced the first-ever galactic portrait using particles instead of light.
This breakthrough was made possible by a collaboration of scientists using the IceCube Neutrino Observatory, located at the Amundsen-Scott South Pole Station in Antarctica and supported by the U.S. National Science Foundation. The observatory consists of thousands of sensors buried deep within a cubic kilometer of pristine ice. It detects high-energy neutrinos from space and provides valuable data. The results of this research were presented at an event at Drexel University and will be published in the journal Science.
The moment Naoko Kurahashi Neilson, a physicist from Drexel University, and her two doctoral students examined the neutrino-based image, they realized its significance. This innovative computational analysis was made possible by funding from the NSF's Faculty Early Career Development program. Denise Caldwell, the director of NSF's Physics Division, emphasizes that breakthroughs in science often rely on technological advancements. The IceCube detector's sensitivity, combined with new data analysis tools, has given scientists a fresh perspective on our galaxy. As these capabilities continue to improve, we can anticipate a clearer and more detailed image of our galaxy, potentially uncovering hidden features that have never been seen before.
Francis Halzen, a physicist at the University of Wisconsin-Madison and the principal investigator at IceCube, highlights the intriguing fact that the universe shines brighter in neutrinos compared to any other form of light. However, detecting and distinguishing neutrinos from other interstellar particles is a challenging task. Determining the source of neutrinos is an even more ambitious goal. When neutrinos interact with the ice beneath IceCube, they produce faint patterns of light, which can be detected. Some patterns point to specific areas of the sky, enabling researchers to identify the sources of neutrinos. These interactions were crucial in the IceCube Collaboration's previous discovery of neutrinos originating from a galaxy 47 million light-years away.
However, some interactions produce less directional patterns, resulting in cascades of diffuse light in the ice. Kurahashi Neilson explains that her colleagues, Sclafani and Hünnefeld, developed a machine-learning algorithm to analyze more than 60,000 neutrino-generated light cascades recorded by IceCube over a decade. After meticulous testing and verification using simulated data, they applied the algorithm to the real data provided by IceCube. The result was an image showing bright spots corresponding to suspected neutrino-emitting locations in the Milky Way. These locations align with areas where gamma rays are observed, which are believed to be produced by collisions between cosmic rays and interstellar gas, a process that should also generate neutrinos.
Sclafani remarks that the measurement of a neutrino counterpart confirms our understanding of the galaxy and the sources of cosmic rays. Over the years, scientists have made numerous astronomical discoveries by expanding their observation methods. They have utilized radio waves, infrared light, gravitational waves, and now neutrinos. Kurahashi Neilson sees the neutrino-based image of the Milky Way as another significant step in this lineage of discovery. She predicts that neutrino astronomy will be refined, just like the methods that came before it, eventually unveiling previously unknown aspects of the universe. For scientists like her, the excitement lies in witnessing something never seen before and gaining a deeper understanding of the universe.