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Neutrinos have been spotted coming from a strange, shrouded galaxy

Cosmic neutrinos are tough to track – it has only been done once before – but researchers from the IceCube observatory in Antarctica have tracked 79 of them back to their home galaxy

Space 3 November 2022

Front view of the IceCube Lab at twilight, with a starry sky showing a glimpse of the Milky Way overhead and sunlight lingering on the horizon.

The IceCube Lab has traced neutrinos back to their home galaxy

Martin Wolf, IceCube/NSF

The IceCube Neutrino Observatory in Antarctica has found a second source for high-energy neutrinos from outer space. These particles are notoriously hard to spot and even harder to trace back to their sources, but they perfuse the entire universe. This finding helps give a better understanding of where they form.

The IceCube researchers, led by Francis Halzen at the University of Wisconsin-Madison, found their first definitive source for a single high-energy cosmic neutrino in 2017: a blazar called TXS 0506+056 blasting a huge jet of energy towards Earth. That finding was made with the help of many other telescopes, but by using an updated method to analyse nearly a decade’s worth of data the team was able to find its second neutrino source, called NGC 1068, without any outside help.

The researchers traced 79 high-energy neutrinos back to this relatively nearby galaxy. “When we first published these 10 years of data, NCG 1068 was there, but we were not sure if it was a background fluctuation or if it was a real source,” says Halzen. “Now we know these are not fluctuations.”

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Cosmic neutrinos are produced when a proton slams into another particle, creating a shower of fundamental particles, some of which later decay and release neutrinos. NGC 1068 seems like a near-perfect environment for this to happen. It is an active galaxy, meaning its central supermassive black hole is gobbling up material and creating powerful radiation as it does so. But its centre is shrouded in a dense knot of gas and dust, which obscures the black hole while giving the radiation something to slam into in order to produce neutrinos.

There are far more active galaxies like this one than blazars similar to TXS 0506+056, so this finding might help explain why there are so many cosmic neutrinos floating around the universe. “The diffuse [flow of neutrinos] we see from the universe is around 100 times larger than what we get from this one source, so there is still room for surprises, but if I were going to bet my wallet it would be on this kind of object,” says Halzen.

The researchers are now working on further refining their analytical methods and upgrading the detector so that we can track more neutrinos and gain a better understanding of how they are made.

Journal reference: Science, DOI: 10.1126/science.abg3395

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