IceCube Telescope Finds High-Energy Neutrinos

[rhoenix]

After years of finding nothing, scientists at the IceCube neutrino telescope have detected 28 high-energy neutrinos that likely came from some of the most violent and powerful explosions in the universe. These are the precise results that IceCube was built for.

“We are seeing these cosmic neutrinos for the first time,” said physicist Francis Halzen of the University of Wisconsin-Madison, principal investigator of the IceCube collaboration. With these particles in hand, astronomers finally have a new window to the universe and may be able to figure out the details of mysterious processes that have so far eluded them. The findings appear today in a paper published in Science.

IceCube is a giant neutrino-finding telescope buried in the cold darkness 1.5 kilometers beneath the surface in Antarctica. With that much frozen weight above it, the ice at this location gets smushed, driving out any air bubbles and making it perfectly clear.

This allows the 5,160 light-sensitive detectors used in IceCube to see faint flashes across a large distance. Trillions of neutrinos pass like ghosts through the cubic kilometer of ice that IceCube is monitoring. Every once in a while, one of these tiny particles will crash right into the oxygen atom of a frozen water molecule, producing a faint blue spark. The flash of light tells scientists the direction and energy that a neutrino had when it flew into the detector.

Astronomers hypothesize that high-energy neutrinos are created in extremely energetic processes in the distant universe. Active galactic nuclei (AGN) and gamma-ray bursts are some of the brightest cosmic events that we see but researchers don’t really know how they work. Scientists speculate that giant black holes and collapsing massive stars are behind these mysteries but have yet to understand their mechanics.

Because they barely interact with anything, neutrinos get created in these events and then easily escape, shooting out in a direct line across the universe. These neutrinos have insane amounts of energy, more than a 1,000 times the energy that protons are smashed at CERN’s Large Hadron Collider. Astronomers hoped that IceCube would see these lively neutrinos, allowing them to trace back where in the sky they arrived from, and help them figure out what’s going on with the unexplained bright sources.

But after being completed in 2010, IceCube took a year’s worth of data and found zilch. Not even one neutrino. Well, that’s not entirely true.

“We actually see a neutrino every six minutes,” said Halzen.

These common neutrinos are created when charged nuclei called cosmic rays hit Earth’s atmosphere, generating a shower of subatomic particles, including neutrinos. After taking data for two years, though, IceCube had yet to see a high-energy neutrino coming in from outside our solar system. The non-detection concerned and frustrated scientists, who thought there might be something wrong in their models.

Then, help came from an unexpected direction. Some members of the IceCube team began looking through their data for ultra-high-energy neutrinos – 1,000 times more powerful than even those created in AGNs and gamma-ray bursts – created when a cosmic ray interacts with the cosmic microwave background radiation.

While combing through the ultra-high-energy data, the IceCube team also unexpectedly found two neutrinos in the right energy range to have come from an AGN or gamma-ray burst. The neutrinos were so rare, the collaboration named them “Bert” and “Ernie.” These two discoveries showed them how to analyze the data and spot the neutrinos the telescope was built to see. Now, knowing how to find the high-energy neutrinos, the team saw 26 more in their data from 2011 and 2012 that they had originally missed.

Most of the 28 high-energy neutrinos so far detected originate from parts of the night sky that don’t include the Milky Way, making it quite likely that they are arriving from a distant source. There are still too few neutrinos to make any specific conclusions about AGNs or gamma-ray bursts, but the IceCube team will continue gathering new data.

Halzen said the team is already using the new tactic to look through their 2013 data. They have found at least one more high-energy neutrino, the most powerful one yet seen, which they are calling “Big Bird.” Halzen said he expects to have enough neutrinos to say something about cosmic accelerator within about five years.

The findings are generating a good deal of excitement in the neutrino astrophysics community.

“I think this paper is one that will go into the textbooks,” said physicist John Learned of the University of Hawaii, who is not involved in IceCube. “It will be recognized as the beginning of high-energy neutrino astronomy.”

Every time scientists open a new window to the universe, they find unexpected things, added Learned. Already, the IceCube data has several new mysteries to ponder, including the fact that some of the neutrinos seem to cluster from a source near the center of our galaxy. If IceCube continues to see neutrinos from this source, it could point to an unexpected and interesting new process. Though scientists don’t know what that might be, “it’s certainly going to be something strange and new,” said Learned.

In short - astronomers detected particles that are so uncaring of normal matter that their existence was more theorized than shown. Now, they've been caught a few times, in a reproduceable fashion. This is how we got cool stuff like X-ray telescopes, and used them to see inside of stars.

So if you see people like Dr. Neil deGrasse Tyson dancing like madmen for no clear reason, this is why.

[rhoenix]

More from another source:

Earlier this year, scientists using a powerful detector at the South Pole discovered Ernie and Bert, two neutrinos with energies over 100 times higher than the protons that circulate in the LHC. Now, the same team has combed through its data to find an additional 26 high-energy events, and they've done a careful analysis to show that these are almost certainly originating from somewhere outside our Solar System.

Neutrinos are incredibly light particles that rarely interact with normal matter; staggering numbers pass through the Earth (and your body) every second. To spot one, you need a very large detector, and IceCube fits the bill. Located in the ice cap at the South Pole, the detector works by capturing the light produced when neutrinos interact with the huge volume of ice present. To do so, holes were drilled up to 2 km into the ice, and strings of photodetectors were lowered into them. All told, they pick up the signals from a cubic kilometer of ice.

The challenge is figuring out which signals come from the out-of-this-world neutrinos. Cosmic rays slam into the atmosphere all the time, and these can produce neutrinos that then enter the ice cap. They can also produce other exotic particles that produce light as they pass through the ice. Muons, for example, only live about 10-6 seconds, but they're moving so fast that time dilation means they live longer from the Earth's frame of reference. As a result, they may travel several kilometers through the ice before decaying.

To handle these cases of background, the authors eliminated any signals that were present in the outermost edges of the detector. Cosmic rays are especially easy to spot given that they tend to produce a spray of particles, many of which will be found at the detectors closest to the surface. You might still get a few neutrinos created above the North Pole and passing through on their way out of Earth, but the authors found that the majority of their signals came from the south, suggesting that these neutrinos aren't a major problem for this detector.

Previously, the authors' analysis only picked up very high-energy events; Ernie and Bert were about one Peta-electronVolt each (for comparison, the LHC's protons are at 4 Tera-eV). Now, they've extended the sensitivity down to as low as 30TeV, with 28 events spread throughout the range of energies between the two. Seven of these produced muons in the detectors, indicating that they were produced by the muon neutrino. The rest produced a shower of signals, suggesting that they originated from some other form of neutrino.

The energies and properties involved in these neutrinos indicate that they originated outside our Solar System. Just as cosmic rays can produce neutrinos when they slam into something nearby, energetic events can produce neutrinos that travel significant distances across the Universe. One example might be if the jets of particles from a black hole slammed into a gas cloud, producing unstable particles like pions that decay in ways that produce neutrinos. Since all that energy ends up in a particle that's only a billionth of the mass of a proton, the neutrinos end up effectively traveling at the speed of light. Meaning that if we can see something anywhere in the Universe, we can also detect any neutrinos it produces.

The downside is that we don't yet have the ability to work backward to figure out the direction that the neutrinos originated from. We can give a rough area of the sky, but it's not good enough to direct observatories to image the source. At least within the IceCube detector, there was also no apparent pattern in time, indicating that it wasn't able to pick up any burst events. Although we're pretty sure these came from outside our Solar System, we can't currently say much about what produced them.