LAKE BAIKAL, RUSSIA – A glass orb, the size of a beach ball, plops into a hole in the ice and descends on a cable toward the bottom of the world's deepest lake. Then another, and another. These light-detecting orbs come to rest suspended in the pitch-dark depths down as far as 4,000 feet below the surface.
This is a telescope, the largest of its kind in the Northern Hemisphere, built to explore black holes, distant galaxies and the remnants of exploded stars. It does so by searching for neutrinos, cosmic particles so tiny that many trillions pass through each of us every second. If only we could learn to read the messages they bear, scientists believe, we could chart the universe, and its history, in ways we cannot yet fully fathom.
"You should never miss the chance to ask nature any question," said Grigori Domogatski, 80, a Russian physicist who has led the quest to build this underwater telescope for 40 years. "You never know what answer you will get."
Scientists believe that as they learn to read the universe using neutrinos, they could make discoveries much as the lensmakers who developed the telescope could not have imagined that Galileo would later use it to discover the moons of Jupiter. "It's like looking at the sky at night, and seeing one star," astrophysicist Francis Halzen said in describing the current state of the hunt for the ghostly particles.
It is still under construction, but the telescope is closer than ever to delivering results.
The Lake Baikal venture is not the only effort to hunt for neutrinos in the world's most remote places. But it will be an important complement to the work of IceCube, the world's largest neutrino telescope, a U.S.-led $279 million project that encompasses about one-quarter of a cubic mile of ice in Antarctica. IceCube identified a neutrino in 2017 that scientists said almost certainly came from a supermassive black hole. It was the first time that scientists had pinpointed a source of the rain of high-energy particles from space known as cosmic rays — a breakthrough for neutrino astronomy.
Halzen, director of IceCube, and his team believe it may have found two additional sources of neutrinos arriving from deep in space — but it is difficult to be certain because no one else has detected them. He hopes that will change as the Baikal telescope expands.
The Baikal telescope looks down, through the entire planet, out the other side, toward the center of our galaxy and beyond, essentially using Earth as a giant sieve. For the most part, larger particles hitting the opposite side of the planet collide with atoms. But neutrinos — 100 billion of which pass through your fingertip every second — continue, essentially, on a straight line. Yet when a neutrino, exceedingly rarely, hits an atomic nucleus in the water, it produces a cone of blue light called Cherenkov radiation.
If you spend years monitoring a billion tons of deep water for unimaginably tiny flashes of Cherenkov light, many physicists believe, you will find neutrinos that can be traced back to cosmic conflagrations that emitted them billions of light-years away.
The orientation of the blue cones even reveals the direction from which the neutrinos that caused them came. By not having an electrical charge, neutrinos are not affected by interstellar and intergalactic magnetic fields and other influences that scramble the paths of other types of cosmic particles. Neutrinos go as straight through the universe as Einsteinian gravity will allow.
That is what makes neutrinos so valuable to the study of the universe's earliest, most distant and most violent events. And they could help elucidate other mysteries, such as what happens when stars far more massive than the sun collapse into a superdense ball of neutrons roughly 12 miles across.
"It travels the universe, colliding with practically nothing and no one," Domogatski said of the neutrino. "For it, the universe is a transparent world."