Deep below the surface of Antarctica, scientists are hunting for ghosts. Tiny particles called "neutrinos" fill the universe, but they're almost impossible to detect. Their mysterious origins have eluded researchers for decades. 
 
 Now, in a discovery that heralds a “new era” of neutrino research, physicists have finally pinned down a source. Researchers probing a huge cube of ice at the South Pole think a violent "blazar" galaxy is churning out the stealthy specks. They reported their results in two papers published in the journal Science. 
 
 The discovery also sheds light on a mystery more than 100 years in the making, helping scientists understand the cosmic rays that radiate throughout the universe. 
 
 “If you stick your thumb out right now, there are one billion neutrinos going through your thumbnail every second. They are going through your [nail], through your body, through everything,” University College London particle physicist Linda Cremonesi told Newsweek. 
 
 But these ghostly particles almost never interact with matter. 
 
 “Every second we have something like 100 trillion neutrinos going through our body, but in our lifetime we will on average interact with just one of them,” said Cremonesi, who was not involved in the research. 
 
 This stealthy travel makes neutrinos the perfect scouts through which to spy on the deepest, darkest parts of the universe. While a single sheet of paper can absorb light’s photons, Cremonesi explained, neutrinos can travel undetected for eons. 
 
 That's the reason this discovery may signal “the beginning of a new era in neutrino astronomy,” she added. But it's also why the particles are so hard to find. 
 
 IceCube/NSF 
 
 “The core difficulty is always the same for everything related to neutrinos: They almost never interact with matter,” Chad Finley from Stockholm University told Newsweek. “The vast majority [of neutrinos] that arrive at Earth will pass through without leaving a trace. This has earned them the name ‘ghost particles.’” 
 
 The IceCube facility at the South Pole hunts for neutrinos like a telescope detects light. But instead of pointing to space, its sensors are buried in a clear chunk of ice buried deep underground. 
 
 Thought to be forged in the churning bellies of nuclear reactors like the Sun, the phantasmagoric specks pour out into the universe—abundant but solitary. Only a small portion will likely ever interact with matter, Finley explained. 
 
 IceCube hunts for “high energy” neutrinos, where a single particle has almost a micro-joule of energy, IceCube researcher Naoko Kurahashi Neilson from Drexel University told Newsweek. The most energetic neutrinos should shed light on the highest-energy astrophysical processes. 
 
 “When a high energy neutrino collides with an atom, a shower of subatomic particles explodes forth in the same direction,” said Finley, who is also an IceCube researcher. 
 
 This interaction creates a faint blue light that passes through the clear, pristine ice. IceCube’s sensors are spread out across about a quarter of a cubic mile, so they're watching about a billion tons worth of hydrogen and oxygen atoms just waiting to bump a neutrino or two, Finley explained. 
 
 Millions to billions of particles travel through IceCube, so a team of top scientists work to filter out the neutrinos from this haze, Kurahashi Neilson said. Some 300 researchers from 49 institutions in 12 countries are involved in this chilly hunt. 
 
 Although IceCube had detected neutrinos before, an event observed on September 22, 2017 finally pointed scientists towards a specific source. This neutrino lined up with a bright object sitting four billion light years away—a blazar called TXS 0506+056. 
 
 Blazars—galaxies surrounding hungry black holes that guzzle on orbiting matter and spurt out plasma jets in the direction of Earth—are some of the most energetic phenomena in existence. 
 
 JPL-Caltech/NASA 
 
 When the team looked back at their research from 2014-2015, they matched up more neutrino events with the same source. This made them pretty confident that—eons ago—the neutrinos had burst from the distant blazar, before slowly making their way to Earth. “We've calculated that there's only a 0.02% chance this is just coincidence,” Kurahashi Neilson said. 
 
 As well as blazars and stars like the Sun, scientists think neutrinos might also come from gamma ray bursts, supernovae remnants, starburst galaxies and other highly energetic astronomical phenomena. But, so far, researchers haven’t linked any of the mysterious particles to these sources. 
 
 If the blazar discovery wasn’t revolutionary enough, the IceCube research also advances scientists' understanding of cosmic rays—high-energy radiation that seeps into our solar system. “[Neutrinos are thought to come from high energy particle collisions where cosmic rays are created. But the sources of high energy cosmic rays are themselves unknown,” Finley explained. "This has been one of the biggest unsolved questions in astrophysics for decades.” 
 
 The new research suggests that blazars might also be a source of this very high energy cosmic radiation. 
 
 Plenty of other neutrino mysteries still await the IceCube Collaboration. Scientists are keen to find out if other blazars are pumping out the particles, and where else the stealthy specks are spurting from. 
 
 “This measurement really launches the field of neutrino astronomy,” IceCube researcher Darren Grant from the University of Alberta told Newsweek. 
 
 “All of astronomy since the dawn of time has been using light. We know where stars are, where galaxies are because we see them in photons,” Kurahashi Neilson said. “Now we want to see what the universe looks like in neutrinos.” 

 Scientists have spotted a high-energy, incredibly tiny "ghost" particle called a neutrino flying through Antarctic ice and traced its origins back to a specific blazar, they announced today, July 12 
 
 Physicists are very excited about the detective work that has told them about the neutrino's birthplace. But what the heck is a neutrino anyway, and why does it matter where the thing came from? 
 
 A neutrino is a subatomic particle just as tiny as an electron, but without any charge. Scientists know neutrinos have a tiny bit of mass, but they can't pin down exactly how little. The result is that neutrinos tend to give other matter the cold shoulder: They don't interact with their surroundings very often, which makes them difficult for scientists to spot. [Tracing a Neutrino to Its Source: The Discovery in Pictures] 
 
 Nevertheless, they're everywhere — your body is pummeled by about 100 trillion neutrinos every second. And scientists think the weird particles may hold the key to some of the biggest mysteries about the universe, including why matter won out over antimatter early after the Big Bang. 
 
 "Neutrinos are awesome," Kate Scholberg, a particle physicist at Duke University in North Carolina, told Space.com. She's biased, since she's spent her career studying the tiny things, but that doesn't make her wrong. "We have to understand them if we want to understand everything." 
 
 The new research is a small step for scientists hoping to do just that. The discovery started at the IceCube Neutrino Observatory near the South Pole in September. Deep inside the Antarctic ice sheet, a grid of detectors traced the path of a single neutrino in 3D. 
 
 An artist's depiction of the IceCube Neutrino Observatory at the South Pole detecting the journey of a neutrino. Credit: IceCube/NSF 
 
 The path was clear enough that the physicists could follow the neutrino's journey backward in a straight line across the universe. In less than a minute, they asked astronomers around the world to turn their telescopes to that region of the sky and note if they saw anything intriguing. And they certainly did ― there was a blazar, a massive source of high-energy light called gamma-rays, in precisely the same neighborhood, and the scientists were able to confirm the blazar as the neutrino's source. 
 
 The process was possible because neutrinos, like photons of light, can cross extremely large distances in the universe in straight lines, without being pulled off course. Other types of high-energy particles can't do that because they are charged. "They come scrambled here," Greg Sullivan, a physicist at the University of Maryland who works with the IceCube Neutrino Observatory and who was involved in the new research, told Space.com. "We can't trace them back to where they come from." 
 
 The challenge has vexed scientists for about a century, since it means they can't identify what type of objects create what type of highly charged particle. The frustration motivated scientists to open IceCube, the only neutrino detector large enough to capture the incredibly high-energy particles born beyond our galaxy, in 2010. 
 
 "Neutrinos held the promise for some time of being able to map the sky like you would with light but at higher energies," Sullivan said. "We can ask questions or try to answer questions that you couldn't otherwise." 
 
 Lower-energy neutrinos are already being harnessed by astronomers through a network run by Scholberg that is waiting to use a burst of neutrinos to spot the next core-collapse supernova in the Milky Way. 
 
 Such a supernova was last observed in 1987, before modern neutrino detectors existed. But when the next one explodes, Scholberg and her colleagues want to use the neutrino burst to alert astronomers in time to catch the light signature. The neutrinos themselves would also tell scientists about what was happening during the event. "You could actually see a black hole being born in the neutrinos," Scholberg said. 
 
 That, like the new blazar research, would be a breakthrough in what scientists call multimessenger astronomy, which uses two or more different categories of data, like light photons, neutrinos and gravitational waves. More types of data mean more overall information about what happened. 
 
 "It's like a big puzzle and we're trying to fill in the pieces," Sullivan said. "By seeing the picture in both different energies and different particles, we can really try to understand the physics of what's going on." 
 
 But Sullivan and his colleagues aren't content to stop at today's announcement. "This is just the first step," he said, adding that physicists are hoping to build a neutrino detector even larger than IceCube. "We have a lot more out there to learn and see." 
 
 Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com. 

 A 4 Billion Light-Year Journey Ends At The South Pole 
 
 Scientists for the first time have been able to pinpoint the source of an extremely powerful version of a neutrino, a ghostly particle that can travel virtually unimpeded through space. 
 
 It's an achievement that opens a whole new way of looking at the universe. 
 
 The neutrino was detected by a South Pole observatory called IceCube that was specifically designed to catch the particles. It consists of a cubic kilometer of ice festooned with more than 5,000 detectors. 
 
 Neutrinos don't interact with much, but occasionally one will strike another particle, giving off a kind of light known as Cherenkov radiation that IceCube's detectors can pick up. 
 
 When a particularly high-energy neutrino is captured, IceCube sends out an alert. 
 
 "We had this neutrino alert in September 2017," says Olga Botner, a particle physicist at Uppsala University in Sweden and a member of the National Science Foundation-funded IceCube scientific team. On Sept. 22, to be precise. 
 
 When the alert went out, a bevy of observatories on Earth and in space started searching the portion of the sky where the neutrino appeared to be coming from, looking for something that might have generated it. 
 
 There had been other alerts prior to last September, but past searches failed to turn up a viable candidate. 
 
 This time, as Botner and her colleagues report in the journal Science, two observatories, NASA's Fermi Gamma-ray Space Telescope and the Major Atmospheric Gamma Imaging Cherenkov telescope, saw a burst of gamma energy coming from the same location as the neutrino. Gamma rays are the kind of radiation one would expect to see from an object generating neutrinos. The object, known colloquially as TXS 0506+056, was something called a blazar approximately 4 billion light-years from Earth. 
 
 "Blazars are very special objects," Botner says. "They are intensely bright galaxies harboring a black hole at the center." 
 
 To confirm that TXS 0506+056 was indeed the source of the single energetic neutrino detected in September, Botner and her colleagues went back through nearly a decade of data IceCube had collected. They found that other energetic neutrinos had been detected from the same location but had not been previously associated with a celestial object. Those results appear in a second Science paper. 
 
 The neutrinos are expelled in jets that shoot out energetic particles from the black hole spinning inside the blazars. 
 
 "Those jets are a very interesting subject for astrophysicists," says astrophysicist Ke Fang, a JSI Prize postdoc fellow working at the University of Maryland and NASA Goddard Space Flight Center. "Because these are direct outputs from those black holes." 
 
 Fang says the hope is that more of these neutrinos will be detected, which should give physicists more information about the physics that govern black holes. 
 
 In fact, studying neutrinos given off by celestial objects will give scientists more information about cataclysmic events such as exploding stars and colliding neutron stars. 
 
 "Astronomy started when people looked at the night sky, and that's light hitting your eyes," says Naoko Kurahashi Neilson, an astrophysicist at Drexel University in Philadelphia and another member of the IceCube collaboration. 
 
 "It's expanded from just visible light to X-rays and gamma rays, and also to infrared and radio waves," she says. 
 
 But light waves and gamma rays and even radio waves are all what scientists call electromagnetic radiation. They differ in wave length, but they're all from the same family. 
 
 "And then here come neutrinos," Neilson says, "which is a completely different way to look at the universe. And gee, I wonder what we can see if we use this whole different way to look at the universe." 
 
 Of course, scientists don't know what they'll find, but then that's the whole point, isn't it? 

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– Astronomers are jazzed about a major milestone being reported in Science: Researchers for the first time have detected the source of a high-energy "ghost particle" known as a neutrino. If that doesn't mean much to you, this from the Washington Post might help put it in context: The development "heralds the arrival of a new era of astronomy in which researchers can learn about the universe using neutrinos as well as ordinary light." NPR puts it similarly: "It's an achievement that opens a whole new way of looking at the universe." And a Duke researcher not involved with the study tells Space.com that these "weird particles may hold the key to some of the biggest mysteries about the universe," adding, "We have to understand them if we want to understand everything." With this latest feat, scientists are closer to doing just that. Neutrinos are called ghost particles because they are incredibly small and difficult to detect. “If you stick your thumb out right now, there are one billion neutrinos going through your thumbnail every second," a physicist tells Newsweek. "They are going through your [nail], through your body, through everything." But the IceCube Neutrino Observatory at the South Pole managed to spot one in September, and scientists there asked astronomers around the world to train their telescopes on the area in the sky from which it came. They discovered it had been generated by something called a "blazar"—these are "intensely bright galaxies harboring a black hole at the center," a Swedish physicist involved in the study tells NPR—a mere 4 billion light-years from Earth. "This is just the first step," says an IceCube physicist. "We have a lot more out there to learn and see."