First neutrino image of an active galaxy

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

The universe is full of mysteries. One of these mysteries concerns active galaxies with massive black holes at their centers. “Today we still don’t know exactly what processes are taking place there,” says Elisa Resconi, Professor of Experimental Physics with Cosmic Particles at TUM. Now his team has taken a big step towards solving this puzzle: Astrophysicists have discovered a high-energy neutrino source in 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 radiation. Only neutrinos can escape the hell at the edges of black holes; these neutrinos have no electric charge and almost no mass. They penetrate space without being deflected or absorbed by electromagnetic fields. This makes them very difficult to detect.

The biggest hurdle in neutrino astronomy has so far been the separation of the very weak signal from the strong background noise created by particle impacts from the earth’s atmosphere. Measurements were made over many years using the IceCube Neutrino Observatory and new statistical methods to enable Resconi and his team to accumulate enough neutrino events for their discovery.

Detective work on endless ice

Located in Antarctica’s ice, the IceCube telescope has been detecting light trails from event neutrinos since 2011. TUM scientist Dr. Theo Glauch. “The statistical evaluation shows a very significant cluster of neutrino influences coming from the direction of active galaxy NGC 1068. This means that we can assume with near certainty that high-energy neutrino radiation is coming from this galaxy.”

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

But how and where are neutrinos produced there? “We have a clear script,” Resconi says. “We think that the high-energy neutrinos are the result of the extreme acceleration of matter around the black hole, pushing it to very high energies. We know from particle accelerator experiments that high-energy protons produce neutrinos when they collide. 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 yet discovered. Resconi, who recently launched an international initiative to build a neutrino telescope several cubic kilometers in size in the Pacific Ocean, in the northeastern Pacific, says more data will be needed to be able to localize and investigate weaker and more distant neutrino sources. Neutrino Experiment, P-ONE. Together with the planned second-generation IceCube observatory – IceCube Gen2 – it will provide data for future neutrino astronomy.