First neutrino image of an active galaxy

For over ten years the IceCube Observatory in Antarctica has been monitoring the faint trails of extragalactic neutrinos. While evaluating the observatory’s data, an international research team led by the Technical University of Munich (TUM) discovered a source of high-energy neutrino radiation in the active galaxy NGC 1068, also known as Messier 77.

The universe is full of mysteries. One of these mysteries involves active galaxies with supermassive black holes at their centers. “Today we don’t know exactly what processes are taking place there,” says Elisa Resconi, Professor of Experimental Cosmic Particle Physics at TUM. Now her team has taken a major step toward solving this puzzle: Astrophysicists have discovered a source of high-energy neutrinos in the spiral galaxy NGC 1068.

It is very difficult to probe the active centers of galaxies using telescopes that detect visible light or gamma or X-ray radiation from space, because clouds of cosmic dust and hot plasma absorb the radiation. Only neutrinos can escape the hells at the edges of black holes. these neutrinos have no electric charge and almost no mass. They penetrate space without being deflected by electromagnetic fields or absorbed. This makes them very difficult to detect.

The biggest hurdle in neutrino astronomy until now has been separating the very weak signal from the strong background noise created by particle impacts from the Earth’s atmosphere. It took many years of measurements using the IceCube Neutrino Observatory and new statistical methods to enable Resconi and her team to collect enough neutrino events for their discovery.

Detective project in the eternal ice

The IceCube telescope, located on the ice of Antarctica, has been detecting the light trails resulting from incident neutrinos since 2011. “Based on their energy and angle of incidence we can reconstruct where they come from,” says TUM scientist Dr . Theo. Glauch. “The statistical evaluation shows a highly significant cluster of neutrino impacts coming from the direction of the active galaxy NGC 1068. This means that we can assume with a probability bordering on certainty that the high-energy neutrino radiation originates from this galaxy.”

The spiral galaxy, 47 million light-years away, was discovered as early as the 18th century. NGC 1068 – also known as Messier 77 – is similar to our own galaxy in shape and size, but has an extremely bright center that is brighter than the entire Milky Way, although the center is only about the size of our solar system. This center contains an “active core”: a giant black mass with a mass of about one hundred million times that of our sun, absorbing large amounts of material.

But how and where are neutrinos produced there? “We have a clear script,” Resconi says. “We believe that high-energy neutrinos are the result of extreme acceleration of matter in the region of the black hole, raising it to very high energies. We know from particle accelerator experiments that high-energy protons create neutrinos when they collide with other particles. In other words : We found a cosmic accelerator.”

Neutrino observatories for new astronomy

NGC 1068 is the most statistically significant source of high-energy neutrinos discovered so far. More data will be needed to be able to detect and investigate fainter and more distant neutrino sources, says Resconi, who recently launched an international initiative to build a neutrino telescope several cubic kilometers in size in the northeastern Pacific Ocean. Neutrino Experiment, P-ONE. Together with the planned second generation IceCube observatory – IceCube Gen2 – it will provide the data for future neutrino astronomy.