The IceCube Observatory in Antarctica has been tracking the light traces of extragalactic neutrinos for over 10 years. An international research team headed by the Technical University of Munich (TUM) detected a high-energy neutrino radiation source in the active galaxy NGC 1068, better known as Messier 77, while analyzing the observatory’s data.
Prof. Dr Elisa Resconi. Image Credit: Andreas Heddergott/TUM
The universe is riddled with secrets. One of these mysteries includes active galaxies with massive black holes at their cores.
“Today we still don’t know exactly what processes take place there,” comments Elisa Resconi, Professor for Experimental Physics with Cosmic Particles at TUM. Her group has now achieved a significant breakthrough in answering this puzzle: they located a high-energy neutrino source in the spiral galaxy NGC 1068.
Since cosmic dust and hot plasma clouds absorb the radiation, it is particularly challenging to study the active cores of galaxies with telescopes that detect visible light, gamma, or X-ray radiation from space. Only neutrinos, which have no electric charge and almost no mass, may escape the infernos at the margins of black holes. They move through space without being absorbed or redirected by electromagnetic fields. They are therefore quite challenging to find.
The greatest challenge in neutrino astronomy has been separating the very weak signal from the substantial background noise caused by particle hits from the earth’s atmosphere. It took Resconi and her team several years of measurements using the IceCube Neutrino Observatory and innovative statistical approaches to accumulate enough neutrino occurrences for their discovery.
Detective Work in the Eternal Ice
Since 2011, the IceCube telescope in Antarctica’s ice has been monitoring light traces caused by incident neutrinos.
Based on their energy and their angle of incidence we can reconstruct where they come from. The statistical evaluation shows a highly significant cluster of neutrino impacts coming from the direction of the active galaxy NGC 1068. This means we can assume with a probability bordering on certainty that the high-energy neutrino radiation comes from this galaxy.
Dr. Theo Glauch, Scientists, Technical University of Munich
The spiral galaxy, which is 47 million lightyears away, was found in the 18th Century. NGC 1068, also known as Messier 77, has a form and size similar to the Milky Way galaxy, but it contains an extremely luminous center that is brighter than the whole Milky Way, despite being only around the size of the solar system. This center contains an “active core”—a massive dark mass with a mass one hundred million times that of the sun that is absorbing massive amounts of material.
But where and how do neutrinos actually get generated there?
We have a clear scenario. We think the high-energy neutrinos are the result of extreme acceleration which the matter in the vicinity of the black hole undergoes, raising it to very high energies. We know from particle accelerator experiments that high-energy protons generate neutrinos when they collide with other particles. In other words: We've found a cosmic accelerator.
Elisa Resconi, Professor, Experimental Physics with Cosmic Particles, Technical University of Munich
Neutrino Observatories for New Astronomy
The statistically most important source of high-energy neutrinos found so far is NGC 1068. Additional data will be required to localize and examine weaker and more distant neutrino sources, according to Resconi, who recently announced the Pacific Ocean Neutrino Experiment, P-ONE, an international endeavor to build a neutrino telescope several cubic kilometers in size in the northeast Pacific. The information needed for neutrino astronomy in the future will be provided by this observatory and the upcoming IceCube Gen2 observatory.