Alien neutrinos reveal new frontier in astronomy at Antarctica's IceCube

Image: IceCube
The IceCube Laboratory at the Amundsen-Scott South Pole Station in Antarctica is the world's largest neutrino detector. Its computer collect raw data on neutrino activity from sensors buried in a kilometer-wide cube of ice. The sensors look for the flashes of light that are emitted when neutrinos strike.

A collection of 28 weird high-energy neutrino hits from far beyond the solar system represents the beginning of a new age of astronomy — and the new neutrino astronomers say they already have more data yet to report.

"This is something we've launched now," the University of Wisconsin's Francis Halzen, principal investigator for the international IceCube observatory in Antarctica, told NBC News. "We're on a mission, so I don't think there's any time for relaxing."

IceCube is the world's biggest neutrino detector, drawing data from light sensors buried within a cubic kilometer of ice at the South Pole. It's taken 15 years for the observatory to get from the drawing board and through its construction phase to this point: In this week's issue of the journal Science, Halzen and hundreds of other researchers in the IceCube collaboration report the first big batch of high-energy neutrinos traced to cosmic sources.

How high-energy? Beyond a quadrillion electron volts, or nearly 100 times more energetic than anything that can be smashed up in the world's most powerful particle accelerator, the Large Hadron Collider. If scientists can reliably trace these neutrinos to their source, they could lead to new maps of the cosmos — and unlock longstanding mysteries of the universe.

"The belief is that the very luminous and energetic sources which produce the highest-energy cosmic rays are also supposed to produce high-energy neutrinos," IceCube spokeswoman Olga Botner of Uppsala University said in a Science video. "We sincerely hope that the neutrinos we have now observed come from these sources, and within a small amount of time we'll be able to perhaps solve the 100-year-old riddle of the origin of cosmic rays."


The magic of neutrinos
There's a kind of magic that surrounds neutrinos: They're ghostly particles that rarely interact with matter, which means they're devilishly difficult to detect. Even if you can detect them, it's hard to distinguish between the cascades of neutrinos created by cosmic rays shooting through the atmosphere and the neutrinos from more exotic sources. That's why more than 5,000 sensitive detectors were buried about a mile down (1.5 kilometers) in the South Pole's ice.

When neutrinos interact with the ice, they spark another kind of particle called a muon, and the muons radiate an ultra-faint blue glow. IceCube's detectors are sensitive enough to measure that glow, and the collaboration's scientists can analyze patterns and intensities of the muon radiation to determine the direction and energy of the neutrinos.

Mapping the cosmic flow of neutrinos could produce a radically different picture of the universe around us.

"Neutrinos are pretty much like light," Halzen explained. "IceCube makes a picture with neutrino beams. The one difference is that neutrinos go through walls. Light doesn't. For example, presumably neutrinos can reach us from spaces close to black holes, where light can never get out."

The IceCube observatory was completed in 2010, at a cost of $295 million. "It was more difficult than we thought," Halzen said. "On the other hand, the performance of the experiment is far better than we promised."

The first two high-energy neutrinos came to light last year, and since then, IceCube's scientists have documented 26 more such events. Those first two neutrinos have been nicknamed Bert and Ernie.

Bert and Ernie?

Image: Bert and Ernie
These two schematics of neutrino detection events were nicknamed Bert (left) and Ernie (right) in honor of the Muppet characters. Ernie had an estimated energy of 1.14 quadrillion electron volts. That's almost 100 times the energy of the highest-energy collision achievable in the Large Hadron Collider.

Alien Muppets
One of the Wisconsin graduate students who was working on IceCube, Jakob van Santen, got tired of referring to the neutrino events by their official numbers (for example, "118545/63733662") and started nicknaming them after Muppet characters on the "Sesame Street" children's show.

"My son was about a year old when the first two showed up," van Santen told NBC News via email. "That may have been what let me get away with giving the events silly names instead of more dignified ones."

The names stuck, and the Muppet tradition continued as more high-energy neutrinos were identified. "We had collaboration-wide phone conferences with very serious discussions about events such as Dr. Strangepork, Mr. Snuffleupagus, Miss Piggy and so on," said Claudio Kopper, another Wisconsin researcher on the IceCube team.

Halzen said the nicknames are much easier to keep track of than numbers, but he's looking forward to the day when the high-energy neutrino events outpace the process of naming each one. "We unfortunately have not run out of Muppet names, but I promise you that we will soon have more neutrinos than there are Muppets," he said.

He said there are more high-energy candidate events that have not yet been published. "You can think of this as a digital map that has only 28 pixels," he explained. "So we have to add more pixels."

Next steps
University of Toronto astrophysicist Ray Jayawardhana, author of the newly published book "Neutrino Hunters," said the IceCube discoveries are a "veritable cornucopia as cosmic neutrino detections go."

"This is only the second batch of neutrinos that scientists have detected coming from beyond our solar system — the first time was Supernova 1987A, which exploded in a satellite galaxy of the Milky Way — so it heralds a new era in neutrino astronomy," Jayawardhana told NBC News in an email. "Neutrinos could give us insights into some of the most ferocious phenomena in the cosmos."

The neutrinos detected by IceCube are more than a million times as energetic as the ones seen in 1987. The next step is to nail down the sources of those high-energy neutrinos. In the Science paper, IceCube's collaborators said they haven't yet analyzed enough detections to find the right patterns.

"I'd be curious to know, for example, whether these particles arrive in bursts, and whether some high-energy neutrinos originate near the center of our galaxy, which is believed to harbor a supermassive black hole," Jayawardhana said. "For now, our best guess is that these high-energy neutrinos originate from monstrous black holes at the hearts of galaxies, or from tremendous explosions known as gamma-ray bursts, which mark the death throes of gigantic stars."

Update for 7:25 p.m. ET Nov. 22: Bert and Ernie are the most energetic of the 28 high-energy neutrinos reported in the Science paper, but that there's an even more energetic event, not described in the paper. That event has been nicknamed ... wait for it ... Big Bird. Halzen referred to Big Bird during an NPR interview in September, and The New York Times reported that the event occurred during the third year of data collection, which wasn't included in the data set for the Science paper.

Image: IceCube explained
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More about neutrinos:

Halzen, Kopper and van Santen are among 277 listed authors of the Science paper, "Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector."

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.