IceCube: Antarctic neutrino telescope

Incredibly abundant, yet extremely difficult to detect, scientists must go to great lengths to catch neutrinos
12 October 2021

Interview with 

Summer Blot, DESY


We’re going to switch tack slightly to talk about another mysterious type of particle, called a neutrino. Like an electron, but with no electrical charge and a very small mass, neutrinos are one of the most abundant particles in the universe. But, because they interact very little with matter, they are incredibly difficult to detect. Nevertheless, understanding them better might lead to some of the answers we’re looking for; but that means that researchers like Summer Blot sometimes need to go to extraordinary lengths to study them, as she told Eva Higginbotham...

Summer - So IceCube is the world's largest neutrino telescope, and it is super cool. It is actually buried into the glacier at the south pole in Antarctica

Eva - How does that work?

Summer - So neutrinos that are coming from let's say, extra terrestrial sources, or even neutrinos that are produced here on earth, they're kind of traveling through our bodies, but they're also traveling through this glacier. And so what we did with IceCube is we actually buried about 5,000 sensors down into the glacier. They start at about 1,500 metres under the surface, and then go down for another thousand metres, and basically these sensors instrument in total a cubic kilometre of ice. And what they do is they pick up the light signals that are produced when a neutrino naturally interacts in the glacier anyway

Eva - So you basically have a ginormous bit of ice that you've got light sensors in that you're using to pick up stuff coming from space?

Summer - Yeah. A cubic kilometre of ice to measure subatomic particles that are coming from many, many, many millions of light years away.

Eva - How do you go about putting the sensors 1,500 metres or whatever down into a glacier?

Summer - This is a great question, yes. There was actually a special drill that was built to build IceCube. And it works by heating up water and then shooting it super fast and in a very controlled way down into the glacier. So you basically melt the ice, deploy your sensors down into the hole that you've just melted, and then you leave the water in the hole and it sort of freezes back up so that your sensors are then literally frozen into the glacier itself

Eva - So what's the benefit of doing this in a glacier?

Summer - So the benefit is that the glacier just provides an incredibly large amount of matter for the neutrinos to interact with. The benefit for us is that the properties, the optical properties of the ice, are simply such that the light signals that neutrinos produce when they've interacted in the glacier, they can travel really, really far distances before they're absorbed in the ice itself. So that gives us the ability with our sensors to pick up more information, more and more of these light signals from the neutrino interactions with every single event that happens. So when the neutrino interacts in the ice and it tears apart the nucleus, it'll produce the shower of secondary particles and they travel along the same direction as the initial neutrino, and they're the ones producing this kind of bluish light. It's called Cherenkov radiation. And our sensors are basically instrumenting a three-dimensional grid in the ice, and so we basically sample this light as it's being produced along the trajectory of the secondary particles. Then we measure how much light was produced and when it was produced, that's what our sensors tell us, and we can therefore sort of track back and sort of trace back, okay, here there was a signal, and then after that there was a signal, and after that... And so you can kind of draw a line between it almost and say, ah, okay, so the neutrino must've been coming from that direction back there, and sort of point back up into the sky and say, is there anything there?

Eva - What's been found so far?

Summer - I'd say that sort of the most exciting thing is really just that these neutrinos coming from the cosmos do exist. So when we built IceCube we thought they were out there, we thought that all of our theories said, yeah, these neutrinos should be out there, but we hadn't actually discovered them until we built IceCube. And at this point in time we've detected enough of these neutrinos that it's pretty well established that they exist and that there are extra terrestrial sources of extremely high energy neutrinos. So what we still don't know is exactly, you know, how they're being produced or where they're being produced. And we have now some hints that they might be coming from certain types of galaxies with black holes in the centre, and a lot of dust and matter, and star formation going on in these galaxies, but we haven't really detected enough of neutrinos yet to say, definitively, yes, these neutrinos are coming from this kind of source and this is how they're being produced. The plan, what we hope to do is, to go from one cubic kilometre up to eight cubic kilometres inside of the ice, and then build an even larger array on the surface. This would basically allow us to detect even more neutrinos at even higher energies and really start to do, what I would say, is much more precise measurements of neutrino production in these very extreme distant sources

Eva - And have you been to IceCube?

Summer - Honestly, it's my favourite place on the planet. It's really unlike any place that I've been before, both in terms of just the sort of natural beauty, which it's just a very flat ice sheet, but somehow there's beauty in that - at least for me! But also in terms of just the kind of frontier spirit of, you know, a hundred people at a time, at most, living in a small sort of station, all working together for this one goal

Eva - It almost sounds like you could be going into space. I'm wondering, what do you eat there? What food is there?

Summer - So there's a greenhouse that during the winter can be used to grow fruits and veggies. Otherwise, a lot of really, really amazing food because - actually I think Anthony Bourdain did an episode once at the South Pole because the cuisine is so good. It's quite expensive to fly, well, let's say anybody or anything, to the South Pole. So the cost of the food then becomes negligible. So sometimes you're having lobster for dinner. Sometimes it's steak. Sometimes it's a beautiful cheese platter, you know, it's, it's actually really good food!

Eva - It's like you go somewhere so expensive that they'll only feed you really expensive things!


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