Science
3:55 pm
Thu November 21, 2013

'Ghost Particles' In Antarctica Offer Glimpse Of Deep Space

Originally published on Thu November 21, 2013 4:54 pm

A new kind of telescope buried deep beneath the ice of Antarctica has, for the first time, seen a signal from distant, violent events. In doing so, it is beginning to paint a picture of a part of our cosmos that has never been observed before.

Pretty much everything we can see in the universe glows. Astronomers capture the light from stars and galaxies using huge telescopes. But even the most powerful telescopes can only see so much. The cores of dying stars, for example, are hidden behind shrouds of gas and dust that light cannot penetrate. Hidden, too, are the edges of black holes.

There is, however another way to see the universe: through the neutrino. Neutrinos are tiny, fundamental particles created in nuclear reactions, such as those inside stars. But unlike light, the neutrino can't be easily deflected. "It's a ghost particle," says Pierre Sokolsky, a physicist at the University of Utah. "It hardly ever interacts."

Trillions of neutrinos are passing through you at this very moment. The vast majority are passing through the ground, through the earth's core, and flying back into space.

For decades Francis Halzen, a physicist at the University of Wisconsin-Madison, has dreamed of capturing a few of these neutrinos. Think of them as sort of the ultimate X-rays. They can shoot through the thickest dust and debris. That means that some neutrinos that reach the Earth have emanated from the cores of exploding stars or the edge of black holes.

"They may allow us to do astronomy that you cannot do with light," Halzen says. "That's kind of the dream."

There's just one little hitch. Since neutrinos hardly ever react with everyday matter, most of them will pass straight through the telescope you're trying to see them with.

A neutrino telescope has to be big, so that a lot of neutrinos go through it; very dense, so that a few will get caught; and transparent, because when a neutrino gets caught, it gives off a flash of light.

Halzen's team came up with the perfect stuff for the job: ice.

"It's the ultimate transparent medium," Halzen say. "I don't think you can make in a lab a medium as transparent as ice."

The team calculated that they would need a cube of ice that was a kilometer in length on each side. To get it, they went to the Amundsen-Scott South Pole Station. The group marked out a huge cube of ice about a mile beneath the surface. They actually called the detector IceCube. The next step was figuring out how to put thousands of light sensors inside. Halzen admits that it seemed like a long shot.

"You know it is crazy. I mean people thought I was crazy when I talked about this," he says.

"They had no idea how they were going to drill into the ice and drop these detectors kilometers into the ice," Sokolsky says.

But they worked out a system. First they used hot water to melt the ice. Then they dropped in strings of detectors. It worked.

Today, in the journal Science, the first results are in. After two years, Ice Cube has caught 28 neutrinos from beyond the solar system. It's a huge milestone for those who have dreamed of neutrino astronomy, Sokolsky says.

"When you see something like this it's really heartwarming," he says, "because it means, not only have you learned something, but this work has not been in vain."

But Francis Halzen says they're still not quite sure what IceCube is looking at. "You know, I don't think we have enough pixels to see the picture," Halzen says.

In the years to come, the researchers hope that the ice telescope will slowly fill in more and more of the "pixels" to reveal the universe's most intriguing hot spots — one neutrino at a time.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

MELISSA BLOCK, HOST:

And I'm Melissa Block.

Now to the South Pole where scientists have developed a new kind of telescope. They've embedded thousands of sensors deep into the ice to study the heavens. Today, researchers announced that this telescope has captured particles given off by violent events outside our solar system.

NPR's Geoff Brumfiel reached out to the scientists to explain.

GEOFF BRUMFIEL, BYLINE: Pretty much everything we can see in the universe glows. Astronomers capture the light from stars and galaxies using huge telescopes. But Francis Halzen has his eye on something else. Halzen is a researcher at the University of Wisconsin, Madison. And he's obsessed with a ghostly particle called the neutrino. Neutrinos are fundamental. They're smaller than atoms. They're smaller than the things that make up atoms. Just like light, they're made inside stars. But there is one important difference.

FRANCIS HALZEN: Neutrinos go through walls and light does not.

BRUMFIEL: He's being modest. Neutrinos don't just go through walls. Trillions of them are passing through you right now. Most of them go straight through ground, through the Earth's core and out the other side.

HALZEN: So they may allow us to do astronomy that you cannot do with light, that's kind of the dream.

BRUMFIEL: Neutrinos are sort of the ultimate X-rays. They can shoot through the thickest dust and debris. So they can see the cores of exploding stars or the edge of black holes. There's just one little hitch. Since neutrinos hardly ever react with everyday matter, most of them will pass straight through the telescope you're trying to see them with.

So a neutrino telescope needs to be very different. It has to big so a lot of neutrinos go through it; very dense, so that a few will get caught; and transparent, that's because when a neutrino gets caught it gives off a flash of light.

Halzen's team came up with the perfect stuff for the job: Ice.

HALZEN: I mean it's the ultimate transparent medium, I don't think you can make in a lab a medium that is transparent as ice.

BRUMFIEL: And where can you find a lot of ice: The South Pole. So they went to the U.S.'s Amundsen-Scott South Pole Station. The group marked out a huge cube of ice about a mile beneath the surface. They actually called it Ice Cube. The next step was figuring out how to put thousands of light sensors inside. Halzen admits it seemed like a long shot.

HALZEN: You know it is crazy. I mean people thought I was crazy when I talked about this.

(LAUGHTER)

PIERRE SOKOLSKY: Yeah. I have to say I thought it was on the edge of possibility.

BRUMFIEL: Pierre Sokolsky is a researcher at the University of Utah who studies high-energy particles from space.

SOKOLSKY: They had no idea how they were going to actually drill into the ice and drop these detectors, you know, kilometers into the ice.

BRUMFIEL: But they worked out a system. First, they used hot water to melt the ice. Then they dropped in strings of detectors.

SOKOLSKY: And it works like a charm now.

BRUMFIEL: Today, in the journal Science, the first results are in. After two years, Ice Cube has caught 28 neutrinos from beyond the solar system. That's enough to show it works, but Francis Halzen says they're still not quite sure what they're looking at.

HALZEN: You know, I don't think we have enough pixels to see the picture.

BRUMFIEL: In the years to come, the researchers hope that the telescope will slowly fill in more and more of the pixels, perhaps revealing the universe's most intriguing hot spots one neutrino at a time.

Geoff Brumfiel, NPR News.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

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