Eavesdropping in the Arctic

Astrophysicist Anna Nelles searches for neutrinos on Greenland’s ice fields. She hopes to gain new insights into processes that occur in space.

In space, two black holes merge to form one, releasing huge amounts of energy. However, the location in the universe where this happened remains quiet and dark. This is because the light cannot escape from the surroundings of the black holes and is absorbed. This is also what happens to most of the particles that are released during this process. Only a small inconspicuous elementary particle penetrates the cloud of dust surrounding the black hole and then travels through galaxies and planets until it finally lands on Earth and penetrates the ice fields of Greenland.

Anna Nelles would like to find this particle. She is professor of experimental astroparticle physics at FAU and a researcher at the Deutsches Elektronen-Synchrotron (DESY) in Zeuthen, Germany. Her research focuses on finding evidence of exactly these particles, known as neutrinos. “Neutrinos are small neutral elementary particles that can be stopped by almost nothing,” Nelles explains. They can penetrate galaxies, planets, walls – and humans. Billions of neutrinos pass through us every second. But we don’t feel a thing as neutrinos only rarely interact with other matter, which is why they are very difficult to detect. However, this is not the case in high energy events such as those in space where extremely large amounts of energy are released. This occurs, for example, when two black holes merge to form one, or when a black hole rips a star apart. “There are various types of neutrinos,” explains Nelles. “The Sun produces many neutrinos and they also exist in our atmosphere. Extragalactic neutrinos are created during extremely high energy processes in the universe. I am interested in these extremely energy-rich neutrinos from space.” The problem is that neutrinos become rarer the more energy they have. “A neutrino like this occurs maybe once per year in a cubic kilometer of ice. This means we have to monitor very large quantities of ice at the same time.”

Eavesdropping on neutrinos in the ice

This is exactly what Anna Nelles and her team are doing in Greenland – with antennas. When a high-energy neutrino interacts with an atomic nucleus, the process generates radio waves that can be detected by special antennas. Anna Nelles says there are two reasons why she is trying to detect neutrinos in Greenland, of all places: “People emit a lot of radiation. Every tablet, every cigarette lighter you click generates radio emissions. We wouldn’t be able to identify the neutrinos because of the large number of background signals. This is why we need an extremely remote location.” In addition, says Nelles, the signals in a block of ice are much easier to map than in the floor, for example, since it would absorb radio emissions. “If we detect a radio impulse out of nowhere in the ice, we know that it must have been a neutrino.”

If you were to take a map of Greenland and mark the highest point directly in the center, you would know where the FAU team is setting up its antennas. At temperatures of minus 20 degrees Celsius, the researchers have to wear thick winter clothing and protective goggles to drill holes in the ground. A canopy protects them from the wind and flying snow. The holes for the antennas have to be 100 meters deep and 23 centimeters wide. A special drill is required to make them: “We use the world’s largest mechanical drill, which is used in glaciology or the study of ice and glaciers,” says Nelles. Each station has three of these holes that contain a total of 24 antennas. Red flags mark the location of the antennas after they have been installed. Electricity is generated using solar panels and wind turbines. 35 of these stations are to be built by 2027 that can collectively monitor 50 cubic kilometers of ice. Eight stations are already in place. This complex construction project is being financed by various sources of funding that the participants have put together. Among others, Nelles contributed an Emmy-Noether-Grant from the DFG. Since the stations operate independently from each other, data is already being transmitted from Greenland to Germany, 3000 kilometers away.

What happens with the data?

The data is analyzed by Nelles and her team in Erlangen and Berlin. To do this, her work has been funded by an ERC Starting Grant since 2023. The European Research Council (ERC) awards Starting Grants to promising young researchers to enable them to establish their own research groups and to independently pursue research projects with great innovative potential. Nelles hopes to gain new insights into the processes that occur in space such as black hole mergers and would like to see something unexpected: “I think it would be a bit boring if we detected just neutrinos that originate from precisely the source that we are observing. I really would like to see at least one neutrino from a completely unexpected source that will turn our known models upside down.”

 

studied physics and business and economics at RWTH Aachen, Germany, and completed her doctorate in physics at Radboud University Nijmegen, Netherlands from 2010. This was followed in 2015 by a period as a postdoctoral researcher at the University of California. Before coming to FAU, she worked as the head of an Emmy Noether research group at Humboldt Universität zu Berlin. Nelles has been professor of astroparticle physics at FAU since 2019. She also works as a researcher at the Deutsches Elektronen-Synchrotron (DESY) in Zeuthen, Germany. Her research has been funded by an ERC Starting Grant since 2023.

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Author: Miriam Weigand

This article is part of the FAU magazine

Innovation, diversity and passion: Those are the three guiding principles of our FAU, as stated in our mission statement. At FAU, we live these guiding principles every day in all that we do – in research, in teaching and when it comes to sharing the knowledge created at our university with society.

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