Unlock the secrets of cosmic rays

In the frozen desert of Antarctica is a massive particle detector, IceCube Neutrino observatory. But looking for the surface of the instrument will be difficult because most of the observatory is trapped under the ice. The International Observatory has been researching neutrinos – massless, charge-less particles that almost never interact with matter. Now, his observations can solve one of the greatest mysteries of astronomy, answering questions about the origin of neutrinos and cosmic rays.

The largest of them

The IceCube Neutrino Observatory covers one cubic kilometer near the South Pole. The instrument covers one square kilometer of the surface and extends to a depth of 1,920 feet (1,500 meters). It is the first gigaton neutrino detector ever built.

While IceCube's photographs often show a building sitting on the snow-covered surface, the real work is done below. The multi-purpose experience includes a surface chart, IceTop, a chart of 81 stations that lie above the chains. IceTop serves as a calibration detector for IceCube, as well as detecting air showers from primary cosmic rays, their flux, and their composition.

The dense inner sub-detector, DeepCore, is the driving force behind the IceCube experiment. Each of the IceTop stations consists of chains attached to digital optical modules (DOMs) deployed on a hexagonal grid spaced 125 meters (410 feet) apart. Each string contains 60 DOMs the size of a basketball. Here, deep in the ice, IceCube is able to chase the neutrinos that come from the sun, from inside the Milky Way, and from outside the galaxy. These ghostly particles are connected to cosmic rays, the highest energy particles ever observed.

[ Related: Tracing a Neutrino at Its Source: The Discovery in Images ]

Mysterious Particles

Cosmic Rays were Discovered in 1912 The powerful bursts of radiation constantly collide with the Earth from all parts of the galaxy. Scientists have calculated that charged particles must form in some of the most violent and unseen objects and events in the universe. The explosive star death of a star, a supernova, provides a method for creating cosmic rays; the active black holes in the center of the galaxies.

Because cosmic rays consist of charged particles, they interact with the magnetic fields of stars and other objects that they pass through. The fields are deforming and moving the path of cosmic rays, making it impossible for scientists to trace them back to their source.

It is here that neutrinos come into play. Like cosmic rays, it is thought that low-mass particles are formed by violence. But because neutrinos have no charge, they go through magnetic fields without changing course, traveling in a straight line from their source.

"For this reason, the search for sources of cosmic rays has also become the search for very high energy neutrinos", according to the website IceCube.

However, the same characteristics that make such neutrinos messengers also mean that they are difficult to detect. Every second, about 100 billion neutrinos pass through one square centimeter of your body. Most of them come from the sun and are not energetic enough to be identified by IceCube, but some have probably been produced outside the Milky Way.

Tracking neutrinos require the use of very clear materials such as water or ice. When a single neutrino crushes on a proton or a neutron inside an atom, the resulting nuclear reaction produces secondary particles that emit a blue light known as Cherenkov radiation.

"Detected neutrinos are like fingerprints and the phenomena where neutrinos are produced", according to the IceCube team

Difficult conditions

The South Pole may be not outer space, but it brings its own challenges.The engineers began construction of IceCube in 2004, a seven-year project that was completed in 2010. Construction work could only take place a few month a year, during the summer of the southern hemisphere, which runs from November to February.

Drilling 86 holes required a special type of drill – two of them, in fact. The first advanced through the fir tree, a layer compacted snow, up to about 50 meters (164 feet). Then a high-pressure hot water drill melted through the ice at speeds of about 2 meters (6.5 feet) per minute, up to a depth of 2,450 meters (8,038 feet) , or 1.5 thousand). were able to produce almost perfect vertical holes ready for deployment of instrumentation at a rate of one hole every other day, "according to IceCube

The ropes were then to be rapidly deployed in the l? melted water before the ice regenerates. The freezing took a few weeks to stabilize, after which the instruments remained untouchable, frozen permanently in ice and unable to be repaired. The failure rate of the instruments has been extremely slow, with less than 100 of the 5,500 sensors currently not operational.

IceCube began making observations early, even while other ropes were being deployed.

According to Halzen, the researchers did not know where the light would travel through the ice. With this well-established information, the collaboration works towards IceCube-Gen2. The improved observatory would add about 80 additional detector chains, while understanding the properties of ice will allow researchers to place detectors more widely than their original conservative estimates. IceCube-Gen2 is expected to double the size of the observatory for roughly the same cost.

An Amazing Science

IceCube began searching for neutrinos before it was completed, producing several intriguing scientific results along the way.

Between May 2010 and May 2012, IceCube observed 28 very high energy particles. Halzen attributes the ability of the detector to observe these extreme events until the completion of the detector

"This is the first indication of very high energy neutrinos coming from outside our solar system, with energies more than a million times those observed in 1987 in relation to a supernova seen in the Great Magellanic Cloud, "Halzen explains in a statement. "It is gratifying to finally see what we were looking for: it is the dawn of a new era of astronomy."

In April 2012, a pair of high-energy neutrinos were detected and nicknamed Bert and Ernie after the characters. from the children's TV show "Sesame Street". With energies greater than 1 petaelectronvolt (PeV), the pair was the first neutrino definitively detected since the outside of the solar system since the supernova of 1987.

"It's a major breakthrough," says Uli Katz, particle physicist at the University of Erlangen. Nuremberg, Germany, who was not involved in the research. "I think it's one of the absolute major discoveries of astro-particle physics," Katz told Space.com

These observations have allowed IceCube to win the prize for 39, year 2013 of Physics World

. December 4, 2012, when the observatory detected an event that scientists called Big Bird, also of "Sesame Street". Big Bird was a neutrino whose energy exceeded 2 quadrillion electron volts, more than a million million times more than the energy of a dental x – ray, packaged in a single particle with less than one millionth of electron mass. At the time, it was the highest energy neutrino ever detected; from 2018, he always ranks second.

With the help of NASA's Fermi Gamma-Ray Space Telescope, scientists linked Big Bird to the very forceful explosion of a blazer known as PKS B1424-418. The blazars are powered by supermassive black holes in the center of a galaxy. As the black hole engulfs the material, some of the material is diverted into jets carrying so much energy that they surpass the stars of the galaxy. The jets accelerate matter, creating neutrinos and atomic fragments that create cosmic rays.

Starting in the summer of 2012, the blazar shone between 15 and 30 times stronger in gamma rays than its average before the rash. A long-term observation program called TANAMI, which routinely monitored nearly 100 active galaxies in the southern sky, revealed that the galaxy's jet core had illuminated four times between 2011 and 2013.

"None Another galaxy observed by TANAMI during the life of the program has shown such a dramatic change, "said Eduardo Ros, of the Max Planck Institute for Radioastronomy (MPIfR) in Germany, in a 2016 statement. Taking into account all the observations, the blazar seems to have had the means, the motive and the opportunity to shoot the Big Bird neutrino, making it our prime suspect, "said the team. Matthias Kadler, professor of astrophysics at the University of Würzburg in Germany. "

In July 2018, IceCube announced that, for the first time, it had traced the neutrinos back to their blazar source, an installed alert system that was broadcast to scientists around the world in the ensuing minutes. the detection of a powerful neutrino candidate, the researchers were able to quickly turn their telescopes in the direction of the signal origin, Fermi warned the researchers of the presence of an active blazar -0506 + 056, in the same part of the sky: new observations have confirmed that the blazar was blazing, emitting shards of energy brighter than usual.

For the most part, TXS is a typical blazar, which is the only one in the world. is one of the 100 brightest blazars detected by Fermi, however, while the other 99 are also brilliant, they have not launched neutrinos to IceCube.In recent months, the TXS has shined, illuminated and dropped up to a hundred times stronger than the previous years.

"The tracking of this high-energy neutrino detected by IceCube up to TXS 0506 + 056 makes it is the first time we Gregory Sivakoff, of the University of California." Alberta in Canada, said in a statement

IceCube is not over yet. The new warning system will keep astronomers on their guard in the years to come. The observatory has an expected life span of 20 years, so there is at least another decade of incredible discoveries from the South Pole Observatory.