At first cosmic, scientists detect "ghost particles" from a distant galaxy

When the sun was young and weak and the Earth was barely formed, a gigantic black hole in a distant, bright galaxy spewed a powerful jet of radiation. Four billion years later, at the South Pole of the Earth, 5,160 sensors buried more than a kilometer under the ice detected a single ghostly neutrino. he interacted with an atom. The scientists then traced the particle to the galaxy that created it.

The cosmic achievement, reported Thursday by a team of more than 1,000 researchers in the journal Science, is the first time scientists have detected a high energy neutrino and were able to identify where it comes from. It announces the advent of a new era of astronomy in which researchers can learn about the universe using neutrinos as well as ordinary light.

It's the most breathtaking and extreme physics. The researchers compared the breakthrough to detecting ripples in space in 2017 caused by the collision of dead stars, which added gravitational waves to the scientists toolbox to observe the cosmos.

Neutrinos are so small that they rarely bump into atoms. to feel them. They do not light, so our eyes can not see them. Yet these same qualities make them invaluable for transmitting information across time and space, scientists say. Light can be blocked and gravitational waves can be bent, but neutrinos are unscathed when they travel from the most violent events in the universe to a detector at the bottom of the Earth.

Scientists call the signals they can detect in space, such as radio waves or gravitational waves or now neutrinos, the "messengers". If you try to understand complex and chaotic phenomena that occur billions of light years away, it is useful to have a messenger like a neutrino: one who does not get lost.

"They are very clean, they have simple ones," said Heidi Schellman, particle physicist at Oregon State University and computer coordinator of another neutrino detection project, Deep Underground Neutrino Experiment. , which was not involved in the new research.

Neutrinos arrive on Earth at varying energy levels, which are the signatures of the processes that created them. By coupling neutrino detections with From bright observations, scientists will be able to answer questions about distant cataclysms, test theories about the composition of the universe and refine their understanding of the fundamental rules of physics.

The high-energy neutrino reported on Thursday was created in the rapid movement of matter around a supermassive black hole in the center of the galaxy. When this black hole generates a jet of bright radiation, and the jet is directed directly to Earth, scientists call the galaxy a "blazar". Subsequent analysis revealed that this blazar had also produced more than a dozen neutrinos several years ago.

The new discovery, from the South Pole IceCube neutrino detector, has also solved a mystery that has puzzled scientists for generations: the source of mysterious cosmic rays? These extremely energetic particles have been detected since 1912, but researchers have not been able to determine what phenomenon could produce particles at such high velocities.

Darren Grant, astroparticle physicist and spokesperson for IceCube, said the scientists had spent 100 years listening to thunder with their eyes closed and never knowing what caused the booming sound. Only when they looked up and they saw that the show finally made sense. Sound and light – or, in this case, cosmic rays and neutrinos – come from the same event.

"That's why it's exciting," said Grant about neutrino detection. "It's a whole new vision of what's going on in the universe."

Our universe is infused with neutrinos, so named because they are uncharged (or neutral) and infinitely puny (about a millionth of the mass of an electron). They are created in nuclear reactions – in power plants, in the center of the sun, and in the midst of even more extreme events – when the protons accelerate, collide, and break into a shower of energetic particles.

. Neutrinos are the second most abundant type of particles in the universe after photons (light particles). If you held your hand to the sky, about one billion sun neutrinos would cross it in one second.

But you would not feel their presence, because these ethereal particles rarely interact with normal matter. Unless a neutrino collides with another particle, it passes undisturbed and undetected matter.

And the reality is that most of what we call "matter" is only an empty space. If a hydrogen atom was the size of the Earth, the proton at its center would insert into the football stadium of the Ohio State. The electron in orbit would be even smaller, and a neutrino could be compared to a solitary ant.

Neutrinos are said to come in "flavors" – called electrons, muons and tau – and on the rare occasions when they collide with each other they generate corresponding charged particles. Many neutrino detectors work by looking for the lightning flash emitted by these charged particles as they move in water or ice.

Flavored spots that we find everywhere but nobody feels; A material that looks solid but is actually almost empty – that's the weird science of particle physics. It is difficult to understand the spirit and it is almost hard to believe.

Yet scientists assure us that they do not manufacture objects. Since the 1950s, when neutrinos were detected for the first time, researchers have observed low-energy versions of these ghostly particles from the sun and a 1987 supernova in a nearby galaxy. Neutrino maps from the Earth's surface have even been used to identify nuclear reactor sites

But high energy neutrinos, generated only in extreme environments where protons are accelerated at astonishing speeds, have been difficult to pin down. . To be detected, a neutrino had to form long ago in a distant cataclysm, travel across intergalactic space, fly across our galaxy, enter our solar system, navigate the Earth, and then interact with a particle who takes care of his own affairs. And, in a process that seems just as unlikely, since the neutrino left its source 4 billion years ago, life on Earth had to spring up, develop, and evolve to the point that "C & # 39; is crazy, "said Chad Finley, astroparticular physicist at Stockholm University, who spent 10 years coordinating efforts to identify neutrino origins for the IceCube. team. "These are particles that rarely interact with anything, it must be the most unlucky neutrino of all time."

On the other hand, he thought, he and his colleagues are lucky humans. In 2005, the National Science Foundation began building the $ 279 million IceCube Neutrino Observatory. Working during the summer of the South Pole, when the sun never sets and temperatures hover at 18 degrees Fahrenheit, scientists and engineers melt tens of kilometers. holes in the ice and dropped spherical sensor chains into them. (Neutrino detectors are usually buried or submerged to filter out other cosmic signals that would obscure the tiny particles.)

The result was a network of sensors scattered over a cubic kilometer of glacier and able to catch a ghost. The sensors record the level of energy and the direction of the lightning flash emitted by the charged particle created when a neutrino crushes into another material. From this information, scientists can extrapolate the energy level of the neutrino and from where it comes from.

Since the end of the observatory in 2010, IceCube scientists have detected dozens of high-energy neutrinos from outside the solar system. But they have never been able to connect these particles with a source that could be observed by conventional telescopes.

Establishing such a connection was a "holy grail of the field," Finley said, largely because of the nexus link between cosmic rays and the enigma. These are extremely energetic protons and atomic nuclei moving in space at almost the speed of light. They are considered one of the threats to humans during a potential mission to Mars: During the long journey of several months in space, cosmic rays would damage astronauts' cells and could cause radiation diseases.

a charge, which means that their path can be deflected by magnetic fields. This allows the Earth's magnetic field to protect us from these powerful particles, but it also prevents scientists from understanding where the particles are coming from.

Extensive research suggests that any process that accelerates protons at such speeds also generates high-energy neutrinos. . So, if IceCube could understand where neutrinos came from – a task made simpler by the fact that neutrinos are so reliable "messengers" – they would also know the source of cosmic rays.

"Neutrinos are the smoking gun," Finley said.

On September 22, an alert reached the international astronomical community: IceCube had seen the signature of a muon neutrino coming just above the right shoulder of the Orion constellation in the night sky. 19659002] Quickly, many scientists began pointing their telescopes in that direction, fixing the right region of the universe in each wavelength of the electromagnetic spectrum. Researchers using the NASA Fermi Space Telescope have seen an explosion of gamma rays from the alleged source. Gamma rays are associated with particle acceleration that produces both neutrinos and cosmic rays.

Other observatories have seen rays of X-rays, radio waves and visible light. Taken together, these sightings revealed a blazar – a giant elliptical galaxy with a supermassive black hole spinning at its core. As a blazar spins, two streams of light and charged particles – one of which is directed toward the Earth – spring out of its poles.

The blazar receives the catchy name "TXS 0506 + 056" – the first known source of a high energy neutrino, and a possible answer to the mystery of century-old cosmic rays.

For the sake of due diligence, Finley suggests that the IceCube team revisit its old data to examine whether other neutrinos came from the same direction. He did not expect to find anything – neutrinos react so seldom that finding more than one source would be like lightning twice at the same place.

So it was shocking to discover that IceCube had logged more than a dozen neutrinos from what they knew now was the same blazar between late 2014 and early 2015. It was so unlikely that Finley would have found to repeat the words uttered by Isidor Isaac Rabi, an American physicist awarded by the Nobel Prize, when he discovered the muon: "

Combined with gravitational wave detection and traditional light astronomy , observing a neutrino from a known source allows researchers to observe the cosmos in three different ways. They say that we are in the era of multi-messenger astrophysics. "(Since gravitational waves are often described as the way we" hear "the universe and light is our way of" seeing "it, some scientists wondered if neutrinos would be the way we" feel "them.)

"Neutrinos are, in some respects, the most reliable. High energy light from distant sources rarely comes to Earth because photons are so reactive that they get lost on the way. Neutrinos, on the other hand, will travel in a straight line from their point of origin to a detector

"It's an absolutely gorgeous messenger," Grant says.

The ghostly quality of Neutrinos also means that they can be used to probe the light of celestial objects can not penetrate. Schellman pointed out that astronomers using regular telescopes can not see beneath the sun's surface, but 30 years of observations of low-energy neutrinos that emanate from the center of our star have allowed scientists to scrutinize its core. By looking at their energy levels, researchers could understand the melting process that creates neutrinos and generates the energy of the sun. This research also revealed that it takes 100,000 years for energy in the center of the sun to reach the surface, "which means that the sun will continue to operate for at least 100,000 years," he said. Schellman.

Neutrinos detected by IceCube are millions of times more energetic than those from the sun, but they offer the same kind of insight in the intense environments from which the particles emanate. The telescopes watching TXS 0506 + 056 could only capture what was happening on the surface of the blazar; neutrinos carry the signatures of processes at their very center.

It is in these extreme environments that the laws of nature are extended to their limits. What neutrinos reveal about the acceleration of charged particles and the voracious behavior of black holes could help scientists refine the rules of physics – or rethink them.

And there are even more energy neutrinos – those that make the powerful IceCube particles virtually wimpy. For Schellman, this suggests that other sources, even more chaotic and cataclysmic, of neutrinos are still waiting to be found.

"There are things we do not even know yet," she said. "It's only the beginning."