First neutrino image of an active galaxy
For more than a decade, the IceCube Observatory in Antarctica has been monitoring the light trails of extragalactic neutrinos. While evaluating the data from the observatory, an international research team led by the Technical University of Munich (TUM) discovered a high-energy neutrino radiation source 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 giant black holes at their centers. “Today we still don’t know exactly which processes take place there,” says Elisa Resconi, professor of Experimental Physics with cosmic particles at TUM. Now her team has taken a big step toward solving this puzzle: The astrophysicists have discovered a high-energy neutrino source in the spiral galaxy NGC 1068.
It is very difficult to examine the active centers of galaxies with telescopes that detect visible light or gamma or X-rays from space, because clouds of cosmic dust and hot plasma absorb the radiation. Only neutrinos can escape the infernos at the edges of black holes; these neutrinos have no electric charge and almost no mass. They permeate space without being deflected by electromagnetic fields or absorbed. This makes them very difficult to detect.
The biggest obstacle in neutrino astronomy so far has been the separation of the very weak signal from the strong background noise caused by the impacts of particles from Earth’s atmosphere. It took many years of measurements using the IceCube Neutrino Observatory and new statistical methods to allow Resconi and her team to collect enough neutrino events for their discovery.
Detective work in the eternal ice
Located in the ice of Antarctica, the IceCube telescope has been detecting the light trails of infalling neutrinos since 2011. “Based on their energy and their angle, we can reconstruct where they come from,” says TUM scientist Dr. Theo glauch. “The statistical evaluation shows a very significant cluster of neutrino impacts coming from the direction of the active galaxy NGC 1068. This means that we can assume with a near certainty that the high-energy neutrino radiation comes 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 – resembles our galaxy in shape and size, but has a very luminous 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 gigantic black body with a mass about a hundred million times that of our sun, which absorbs large amounts of material.
But how and where are neutrinos generated there? “We have a clear scenario,” Resconi says. “We think that the high-energy neutrinos are the result of extreme acceleration that the matter near the black hole undergoes, causing it to rise to very high energies. We know from experiments with particle accelerators that high-energy protons generate neutrinos when they collide with other particles.” In other words, we have found a cosmic accelerator.”
Neutrino Observatories for New Astronomy
NGC 1068 is the most statistically significant source of high-energy neutrinos discovered to date. More data is needed to locate 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, the Pacific Neutrino Experiment. P-ONE. Together with the planned second-generation IceCube observatory – IceCube Gen2 – it will provide the data for the neutrino astronomy of the future.
IceCube Collaboration: Evidence for Neutrino Emission from Nearby Active Galaxy NGC 1068
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