June 24, 2024

Science – the Milky Way through the eyes of neutrinos – Wikiwand

Madison (dpa) – With the help of ten years of measurements at the IceCube’s one cubic kilometer detector system in Antarctic ice, an international team of researchers has succeeded for the first time in detecting high-energy neutrinos from our Milky Way galaxy. Previously, IceCube had only recorded high-energy neutrinos from distant galaxies. Although theoretical considerations had predicted similar particle radiation from the Milky Way, astronomers have so far searched for it in vain. The scientists reported in Science that only using modern methods of machine learning made the signal visible in the data collected by the detector.

Neutrinos are shy fellows: they rarely interact with ordinary matter. In order to detect volatile particles, large amounts of matter are required, which consist of as pure substances as possible and can interact with neutrinos. Such a substance, for example, is water – and in Antarctic ice it is found in large quantities in a sufficiently pure form. If a neutrino interacts — which rarely happens — with a water molecule, electrically charged particles are formed that race through the ice at nearly the speed of light and emit light, something called Cherenkov radiation.

Where do neutrinos come from?

Researchers are looking for this light using the IceCube. This is – the name says it all – an ice cube. Huge ice cube: one kilometer long. Physicists in the “IceCube” project plunged a total of 5,160 photomultipliers to a depth of 2.5 kilometers into one cubic kilometer of Antarctic ice. In this way, not only can they capture Cherenkov light, but they can also determine the direction it is coming from — and thus also the direction of origin of the neutrinos.

Neutrinos play an important role in nuclear physics, for example in nuclear fusion inside the Sun. But the neutrinos IceCube is looking for are millions to billions of times more energetic and are produced in stellar explosions near supermassive black holes in distant galaxies. But also in our Milky Way, the interaction of cosmic rays with gas and dust should produce high-energy neutrinos, along with gamma rays. But while this gamma radiation can be detected by satellite observatories, the search for galactic neutrinos has so far been unsuccessful.

Filtered out the noise

The problem: Cosmic radiation also produces neutrinos in Earth’s atmosphere – and that noise is superimposed on the signal from the Milky Way being searched for. However, by improving their methods, the IceCube researchers have now succeeded in making neutrinos from the Milky Way visible. On the one hand, scientists have filtered out events that come from the southern sky and thus from the direction of the center of the Milky Way.

To determine the exact origin of the recorded neutrinos, a machine learning-based method developed primarily at TU Dortmund was used. “These improved methods mean that we have been able to use about ten times more neutrinos for evaluation than before, and with better directional accuracy,” explained Mirco Hünnefeld of TU Dortmund. “Overall, our analysis was three times more sensitive than previous research methods.”

Evaluating the IceCube data in this way for the first time imaged the Milky Way as it would appear with neutrino eyes. “This image confirms what we know so far about the Milky Way and cosmic rays,” IceCube researcher Steve Sclafani said. But this is just the beginning. “IceCube” data collection continues and methods need further improvement. “So we get an image with better and better resolution,” explained Denise Caldwell of the “IceCube” project. In this way, scientists want to know exactly where neutrinos originate from. “Of course, we also hope to discover previously unknown and never-before-seen structures in our Milky Way.”

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