Space telescope dunked in Lake Baikal in hunt for ghostly particles

The Baikal Gigatron Volume Detector (Baikal-GVD) has been under construction since 2015, and is the successor to the Baikal Deep Underwater Neutrino Telescope which has been used to study atmospheric neutrinos (produced when cosmic rays strike atomic nuclei in Earth’s atmosphere) from the lake for almost 20 years.

Baikal-GVD is the result of a collaboration between research groups in the Czech Republic, Germany, Poland, Russia, and Slovakia.

It is one of the world’s largest underwater space telescopes. In several years, it will expand to cover one cubic kilometre, rivalling Ice Cube: a giant neutrino observatory beneath the Antarctic ice near a US polar research station.

The instruments are contained within spherical glass bulbs joined by cables to float at a range of depths below the surface. Its modules were taken 4km from the shore of Lake Baikal and submerged through a rectangular hole in the ice to depths of 750-1,300m in the freezing, pristine waters.

Baikal is the world’s deepest lake and largest freshwater lake.

“Lake Baikal is perhaps the only lake where a neutrino telescope can be deployed due to its depth,” said Bair Shoybonov, a senior researcher at the Joint Institute for Nuclear Research, in an interview with AFP. “We need the greatest possible depth, over 1km.”

“Freshwater is also important for its transparency. We also have an ice covering last two to two-and-a-half months which is very important for the deployment of the telescope.”

Dmitry Naumov, also of the Joint Institute, told AFP at the submersion: “A neutrino telescope measuring half a cubic kilometre is situated right under our feet.”

Neutrinos are frequently compared to ghosts due to their elusiveness; they have very little mass compared with other particles and they do not interact with the electromagnetic force (as all charged particles do) meaning that they pass through objects with barely a trace, like ghosts. They only interact with other matter particles through the weak nuclear force responsible for radioactive decay.

Neutrino observatories must be very large in order to detect a significant number of neutrinos, and they are usually located underground to minimise background radiation. For instance, Japan’s Super Kamiokande observatory is located 1,000km below ground in a mine. It consists of a 40m deep tank of ultrapure water, surrounded by 13,000 photomultiplier tubes which detect Cherenkov radiation produced by the interaction of a neutrino with electrons in water.