Most telescopes sit on a mountaintop and look up. This one is frozen into the ice about a mile under the South Pole, and on Tuesday it won the Nobel Prize in Physics.
The prize went to Francis Halzen, a Belgian-born physicist at the University of Wisconsin-Madison, who first pitched the idea back in 1988. His telescope is called the IceCube Neutrino Observatory, and almost none of it is visible.
All that shows on the surface is a small lab on stilts, which would fit right in with our roundup of infrastructure that looks like science fiction. The telescope itself is underneath. A full cubic kilometer of ice, strung with 5,160 glass sensors.
Fair warning, it took us a few reads to get our heads around all this, and we’re still not sure we fully have. So what is it looking for? Neutrinos, the shyest particles we know of. They have no charge and almost no mass, and they sail through walls, people and entire planets without touching a thing. After light itself, they’re the most common particle in the universe.
About 100 trillion of them pass through your body every second! IceCube’s own team figures a detector the size of a person would wait around a hundred years to catch just one.
Halzen’s hunch was that Antarctica had already built the detector for him. The ice deep under the pole has been squeezed for so long that the air bubbles are gone, which leaves it extremely clear. It’s also completely dark.
Every so often a neutrino does hit an atom in that ice. When it does, it kicks out particles moving faster than light can travel through ice, and they leave a faint trail of blue light that can stretch for more than a kilometer. The sensors catch that glow, and from the pattern physicists can work out where the neutrino came from.
Our favorite part is that IceCube spends much of its time looking down. Neutrinos are the only particles that can pass through a whole planet, so anything that arrives from below has to be one. It’s a telescope at the South Pole that uses the Earth as a filter to watch the northern sky. That still bends our brains a little, so we drew it.
They built it with hot water
To get the sensors down there, the team melted their way in. A custom drill shot hot water through a high-pressure hose, sinking holes about 60 centimeters wide and nearly two and a half kilometers deep.
Each hole took about 48 hours and turned some 200,000 gallons of ice into water. The hose alone weighs 25,000 pounds.
Then they had to hurry. Crews clipped 60 sensors onto a cable, lowered it into the water, and let the hole freeze shut around it. They did that 86 times.
Work was only possible in the polar summer, roughly November through February, so it took seven seasons. The last string went in on December 18, 2010.
Once a string freezes in, nobody can get to it again. Any fixing has to happen from the surface, by software. Fewer than 100 of the roughly 5,500 sensors have quit since.
Also, every string has a theme and every single sensor has its own name, which we find very charming!
What it has found so far
In 2013, IceCube caught its first high-energy neutrinos from far beyond our solar system. Nobody could say what was making them.
Then on September 22, 2017, a single neutrino lit up the array. IceCube sent out an alert, about 20 observatories on the ground and in orbit turned to look, and together they traced it to a blazar called TXS 0506+056. That’s a galaxy with a giant black hole at its center.
A second galaxy, NGC 1068, followed in 2022. That’s two so far. It’s early days for this kind of astronomy.
In 2023 came the one we like best, the first picture of our own Milky Way made with neutrinos instead of light. File it next to our look at the size of the universe.
Halzen was born in Tienen, Belgium, in 1944 and has been in Madison since 1972. That makes this a 38-year project for him, from first pitch to the phone call. Honestly, we can’t think of many ideas we’d stick with for that long.
He won it alone, too, which hasn’t happened in physics in more than thirty years.
He took the committee’s call in Italy and said the news felt “strange.” Then he gave the credit to his collaborators.
They aren’t done, either. An upgrade went in over the last polar summer, and there’s a proposal for a successor called IceCube-Gen2 with eight times the volume.
Two people from the team stay at the pole all year to look after it, right through the long, dark winter. And the ice they’re standing on slides about ten meters a year, all in one piece. So the whole telescope is very slowly on the move.
Images courtesy of the IceCube Collaboration and the U.S. National Science Foundation. See more from our Science archive.
