Underwater Telescope Hunts Ghost Particles from Space
A ceremonial launch of the Baikal-Gigaton Volume Detector (GVD) telescope, in Russia’s Lake Baikal on March 13, 2021.Alexei Kushnirenko\TASS via Getty Images
A new telescope below the surface of the world’s deepest lake has commenced a hunt for the universe’s most elusive particles.
These tiny particles, neutrinos, have almost no mass and no electrical charge, which makes them challenging to observe. Most neutrinos that exist today formed during the Big Bang, so studying them can offer insights into why our universe looks the way it does, as well as clues about mysterious forces like dark matter.
Russia’s Lake Baikal provides a perfect medium for scientists to observe neutrinos because these particles emit detectable light as they zoom through clear water. The lake’s depth can also shield the detector from radiation and interference.
So earlier this month, an international group of scientists launched the Baikal-Gigaton Volume Detector, the largest neutrino telescope in the Northern Hemisphere. The detector is now submerged between 0.4 miles and 0.8 miles below Lake Baikal’s surface. It measures one-tenth of a mile wide, long, and tall.
The researchers behind the Baikal-Gigaton Volume Detector, or Baikal-GVD, have been working on the project since 2015. The group hails from the Czech Republic, Germany, Poland, Russia, and Slovakia. According to Russian news agency TASS, the neutrino telescope cost close to $34 million.
Hunting For ‘Ghost Particles’
Neutrinos are the most abundant particles in the universe – about 10 trillion of them pass through your body every second, with you none the wiser. But they’re notoriously hard to detect because they tend to pass through matter without being absorbed by it the way other particles are.
Hence the nickname “ghost particles”: Neutrinos aren’t affected by magnetic fields, and their neutral charge means they don’t interact with anything. They also move at the speed of light.
But when neutrinos travel quickly through water, they emit energy known as Cherenkov radiation, which produces light.
“If an airplane is going very fast, faster than the speed of sound, then it’ll produce sound – a big shockwave – in a way a slower object doesn’t. In the same way, a particle passing through water, if it’s going faster than the speed of light in water, can also produce a shockwave of light,” Yoshi Uchida, a physicist at Imperial College London, previously told Insider.
That’s why the scientists chose Lake Baikal: Its depth and clear water maximize their ability to observe these shockwaves of light. Pristine water means there will be a higher chance that radiation from the neutrinos hits the modules in the detector. And the bigger the lake, the larger the telescope can be – and the more neutrinos it can spot. The lake is just over a mile deep and nearly 50 miles across.
“Lake Baikal is the only lake where you can deploy a neutrino telescope because of its depth,” Bair Shoibonov, one of the Baikal-GVD scientists, told AFP.
“Fresh water is also important, water clarity too. And the fact that there is ice cover for two, two and a half months is also very important,” he added.
Other neutrino detectors have been built underground to stop particles that can’t pass through matter from getting in. The lake’s depth and ice cover acts as a similar barrier.
The GVD resembles a giant octopus: It has eight clusters with eight strings each, and each string is peppered with at least a dozen light-detecting modules.
These arms undulate under the water, waiting for neutrinos to collide with them. Each glass module looks like a see-through globe, as pictured above. So far, the GVD has 288 modules.
Each of the clusters’ eight strings is fixed to the lakebed by heavy anchors.
Neutrinos Could Offer Clues About the Early Universe
Neutrinos may be able to help researchers solve some of the biggest puzzles about the early days of the cosmos 13.8 billion years ago.
One particular conundrum is that scientific models of the Big Bang suggest that matter and its counterpart, antimatter, should have been produced in equal parts. These two oppositely charged types of matter should then have destroyed each other on contact, leaving an empty universe.
That obviously wasn’t the case. Instead, something tipped the scales in favor of matter. It’s possible the same process even created matter’s shadowy cousin, dark matter, at the same time. So scientists hope that by studying neutrinos and tracing them back to their origins in space, they might learn more about what happened during the universe’s critical first moments.
Not all neutrinos that this telescope detects will have come from the Big Bang, though. Some existing neutrinos form from nuclear reactions – in nuclear power stations, particle accelerators, or nuclear bombs – or in the sun and other stars as they form, collide, or die. Observing neutrinos that come from some of these other cosmic sources could enhance researchers’ understanding of the evolution of stars and the inner composition of the sun.
The Baikal-GVD is only about half the size of the largest neutrino detector on Earth, the IceCube South Pole Neutrino Observatory in Antarctica. Both use the same type of modules to detect neutrinos.
But in the future, the Baikal-GVD scientists hope to double the new telescope’s size by adding more modules.