If you google "Messier 77", you will see a possibly familiar image of a bright, dusty spiral galaxy. It is located about 47 million light-years from Earth in the constellation of the Whale. The Hubble Space Telescope last photographed them in 2013. Under all the dust hides a supermassive black hole, which produces intense radiation. Now the international IceCube collaboration reports in "Science" that it has found evidence that the galaxy is also a source of high-energy cosmic neutrinos. The discovery could pave the way for using cosmic neutrinos for astrophysical measurements. With their help, the origin of the high-energy cosmic radiation that reaches us every day from the depths of the Milky Way and other galaxies could be fathomed and the mystery of dark matter could be solved.
"This observation marks the beginning of a real neutrino aastronomy," said Janet Conrad, IceCube member and professor at the Massachusetts Institute of Technology, to the "Physics Magazine". "We have worked and fought for so long to see potential cosmic neutrino sources with very high meaningfulness, and now it is finally time," she said. "We broke a barrier."
The neutrinos, once dubbed ghost particles, are created in very different ways: some have been around since the Big Bang, others are formed when cosmic rays collide with the Earth's atmosphere. The Sun is also a source of neutrinos. It is from the nuclear reactions inside them that most of these particles that hit the Earth originate. They fly almost unhindered through the universe and even through the Earth. Several quadrillions of them flow through us every second. And then there are the extremely high-energy cosmic neutrinos. Their origin gives the researchers a lot of riddles. Where in the cosmos are the particles accelerated so extremely? The fact that neutrinos interact so little with matter is problematic when it comes to detecting them, but it is advantageous if you want to trace the path that such a particle has taken from its source to Earth.
IceCube is a high-energy neutrino observatory near the Amundsen scott research station in the Antarctic. At several kilometers and on an area of around a square kilometer, more than 5000 highly sensitive optical measuring modules are embedded in the ice in the size of a basketball. When an incident neutrino collides with the atomic nucleus of an ice molecule, light is created that is registered by the measuring modules. From the arrival times of the light on the individual sensors, it can be calculated from which direction the neutrino came and what energy it had. In this way, cosmic neutrino sources can be located and perhaps also explored their interior in the future.
In 2018, IceCube discovered the first cosmic neutrino source to be assigned to the very distant Blazar TXS 0506+056. However, the electromagnetic signals that come from the blazar did not match those that would be expected from neutrinom models. The researchers were therefore very interested in tracking down other cosmic neutrino sources. The IceCube collaboration has had "Messier 77" on the radar for several years.
The more than 400 researchers from 63 different universities from all over the world, including 11 German institutions, were looking for neutrino emissions of astrophysical objects in the data recorded between 2011 and 2020. Then they compared the positions of 110 known gamma ray sources individually and subtracted the "background noise" of the ghost particles that are constantly pounding on us. So they found that a surplus of a good 79 Neutrinos in extremely high TERA electron volt energies comes from the direction of "Messier 77" and the galaxy could thus be another high-energy neutrino source.
With the recent findings, IceCube has come a step closer to the answer to the centuries -old question of the origin of cosmic radiation. In addition, these results indicate that there could be many other similar objects in the universe that have not yet been identified. In any case, Elisa Resconi, professor of physics at the Technical University of Munich, is certain: "The unveiling of the hidden universe has just just started, and Neutrinos will lead a new era of discoveries in astronomy."
