Special telescope measures neutrino with highest energy ever
Even with state-of-the-art technology, it is almost impossible to see: a cosmic neutrino. Yet scientists have managed to image this particle with a deep-sea telescope. And that could help to better understand our universe. Leiden particle physicists collaborated on this ambitious project, published today in Nature.
‘Neutrinos are the least understood particles of the standard model. They are almost massless, hardly interact with other matter and they constantly switch identities. If we understand them better, they might also help find explanations for the so far unknown so-called ‘dark matter’, Dorothea Samtleben explains, associate professor at Leiden University and programme leader of the Neutrino research group at Nikhef. ‘I think it's great to study something you can barely see!’
The detection of the neutrino by the telescope
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Watch the video on the original website or‘We have long dreamed of being able to do astronomy with these energy-rich neutrinos,’ says Professor Maarten de Jong. ‘But neutrinos are very difficult to detect, they fly through everything. But very occasionally one collides with an atom and then a flash of light is produced. To see these, you have to build huge telescopes in special locations. Our telescope ‘KM3NeT’ detects collisions of neutrinos with atoms in water and is located at a depth of 2,400 to 3,500 metres, on the seabed of the Mediterranean Sea.’
Except for photons, neutrinos are the most abundant particles in the universe. They have no electrical charge and have almost no mass. They probably arise during the most extreme cosmic processes, for instance when black holes gobble up all the surrounding matter. In the collisions that then occur, these particles are hurled away into space at almost light speed.
The KM3NeT-collaboration (Cubic Kilometre Neutrino Telescope) brings together more than 360 scientists, engineers, technicians and students from 68 institutions from 21 countries around the world, including the Netherlands: Nikhef, Leiden University, NWO-I, University of Amsterdam, NIOZ and TNO.
The grand prize
‘With this neutrino observation, we have already won the grand prize,’ beams Dorothea Samtleben. This measurement provides the world’s first evidence that neutrinos with such high energies are produced in the universe. After a long period of analysis and interpretation of the data, the results appear today in Nature.
On 13 February 2023, the telescope detected an extraordinary signal corresponding to a neutrino with an energy of about 220 million billion electron volts.
Samtleben: ‘The chances of us seeing such a magnificent neutrino again in the next few decades are very small. We will collect more and more lower-energy neutrinos with our growing detector, which will help us learn more about the properties of neutrinos. We can also expect new insights about cosmic sources.’
KM3NeT’s US competitor has been measuring with a much larger telescope for 15 years. They have never measured a cosmic neutrino with this enormous amount of energy before. De Jong says: ‘Yes, I sit and watch it again from time to time, and it never ceases to amaze me! It was right on target. Usually, you see some kind of glancing shot. This was a measurement straight through our detector.’
Telescope design with a Leiden touch
The underwater neutrino telescope on the French and Italian coast consists of a network of detectors - also called Digital Optical Modules (DOMs). These thousands of cameras record flashes of light created when cosmic neutrinos interact with water molecules. Deep in the sea, you don't suffer from interference from other particles affecting measurements.
Due to the selected cookie settings, we cannot show this video here.
Watch the video on the original website orDe Jong: ‘In a few years, the telescope will consist of 230 cables with DOMs in Italy and 115 cables with DOMs in France, all anchored in the seabed. Currently, 13% of this system is in operation. It is a design to which Leiden optics experts have contributed a lot. At a workshop with industry on photosensors, we suddenly came up with the idea of using lots of small cameras and linking them together with accurate calibration. This idea underpinned the final design of the telescope and has been adopted in other places around the world.’
A new window on our universe
Based on a single measurement of cosmic neutrinos, it is impossible to draw firm conclusions about their exact origin. With the ongoing expansion of the KM3NeT telescope, the telescope’s sensitivity will keep improving, which will also increase its ability to locate cosmic neutrino sources.
This first-ever detection of a neutrino of hundreds of PeVs opens a new chapter in neutrino astronomy and offers a new perspective on our universe. Scientists can also start comparing their insights with knowledge from research into other cosmic signals, including electromagnetic waves and gravitational waves.
All this research will eventually bring us closer to more knowledge about the formation of supermassive black holes in the centre of galaxies, supernova explosions and gamma-ray bursts. In this way, we learn to understand the universe and its origins better and better.
Read the article in Nature.
Read the Nikhef press release.