A Earth constantly encounters particles of very high energy from space. The Austrian physicist Victor Hess discovered this "cosmic radiation" in 1912 with a measuring balloon. Their origin has remained mysterious for a long time. At first, we could not imagine a mechanism that accelerates particles at such gigantic speeds.
At least part of the mystery of cosmic radiation has now been solved. It is obviously black holes in the center of the galaxies, which act as accelerators of cosmic particles and can bring the particles to their maximum speed. The scientists report a total of 18 observatories in the journal "Science". Theorists had considered this possibility for some time. Now it has been confirmed for the first time by measurements.
A Journey of Four Billion Light Years
The story of this discovery is extraordinary. It begins with a single ghostly particle recorded by a neutrino detector under the ice of the Earth's South Pole after a four billion light-years-light journey in space on September 22, 2017. It has an extremely high energy and comes from the direction of the constellation of Orion. From the measured data, the researchers were able to determine the direction of neutrino incidence with a precision of about half a degree
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Neutrinos are electrically neutral particles of very low mbad. You can fly through the material virtually unhindered – even across planets, stars and our bodies. Because neutrinos hardly interact with their environment, these as autistic particles can be detected only with great effort. After all, they rarely interact
An Absorbed Neutrino Generates a Flash of Light
At the South Pole, an international research consortium led by the University of Wisconsin at Madison operates a neutrino detector called IceCube. German researchers, especially researchers at the German electron synchrotron (Desy) in Zeuthen and the Technical University of Munich, are also involved in the project.
The Antarctic neutrino detector comprises a total of 5160 light sensors aligned as pearls. were sunk in 86 holes by 2,500 meters deep in the ice. The measurement volume of this ice detector is of one cubic kilometer. A neutrino that is absorbed in this volume of ice generates a flash of light that the surrounding sensors record.
IceCube Detectors in the Antarctic Ice
Source: DESY / Helmholtz Association
Such a rare event occurred on September 22, 2017. Immediately, IceCube researchers rang Alarm and have asked colleagues at other observatories to direct their instruments to the sky region. He began a search operation until here unique in the history of astronomy.
A Concrete Galaxy as a Place of Origin
The Very Large Array antennas of the National Science Foundation (NSF) in the United States were also aligned with the region of origin of the neutrino. The "Fermi" gamma-ray satellite, the Magic detector on the Canary Island of La Palma, which can record the blue-green Cherenkov light generated by cosmic gamma particles in the atmosphere, has also been activated.
Earth-bound gamma telescopes Hess, Hawc and Veritas, the Italian "X-ray" X-ray satellite, the Nasa "Swift" and "NuStar" x-ray satellites, the Esa "Integral" satellite, and seven optical observatories at the global scale.
Collaborative research has been successful. In all ranges of wavelengths – radio waves to hard gamma radiation – galaxy TXS 0506 + 056 has shown increased activity. With a high probability, this galaxy was also the starting point for neutrino capture from the South Pole. For the first time, a concrete celestial object could be badigned to a high-energy cosmic neutrino as a place of origin.
A black hole in the center
However, at the beginning there were still several candidates for the origin of the neutrino. Researchers from the UT Munich and the European Southern Observatory Eso carefully compared the radiation data of the different candidates and then clearly identified the galaxy TXS 0506 + 056 as the source. "We were able to show that the energy of the gamma radiation of TXS 0506 + 056 corresponded perfectly to the energy of the neutrino, which allowed us to exclude all other sources," says Paolo Padovani, Eso researcher. The video could not be read. Please try again later.
On September 22, 2017, researchers discovered a very high energy neutrino at the "IceCube" measuring station at the South Pole. Thanks to this high energy, they were able to determine for the first time the origin of a neutrino.
Source: WELT / Kevin Knauer
In the center of the galaxy TXS 0506 + 056 is an active black hole devouring large amounts of material. This is apparently not only the origin of the high-energy gamma light that radiates this system, but also responsible for the ultra-fast neutrinos, which IceCube has captured one of them. The neutrino had an energy of 300 tera-electrons-volts. In comparison, in the largest and most powerful particle accelerator in the world, the CERN Research Center's LHC near Geneva, protons can only be accelerated to one-fortieth of this energy. If we had to indicate the speed of the neutrino as a percentage of the speed of light, that would give a 99.9 … with 27 others after nine – at least, since the neutrino mbad is not yet well known and that there is only one upper limit
Ray, aimed at the Earth
And it happens in the galaxy TXS 0506 + 056: The strong gravitational forces of the hole black form a hot and rotating disc of matter in its environment, also called accretion disk by researchers. The charged particles, accelerated by powerful magnetic fields, fly in space at almost the speed of light – in a highly focused jet or jet, as the researchers say.
The constellation Orion. The blue reticle marks the galaxy TXS 0506 + 056
Source: Akira Fujii
In the case of TXS 0506 + 056, this jet coincides with the Earth. Galaxies with this property are called blazars. This term was coined in 1978 at an international conference in Pittsburgh. "The Blazar TXS 0506 + 056 is one of the brightest and most bizarre objects ever seen," says Elisa Resconi, a researcher at the IceCube of the Technical University of Munich, who collaborated with Paolo Padovani on the current version.
The Blazar beam initially contains only charged particles, that is, protons, electrons, or atomic nuclei. From now on, they run like cosmic rays through space. But when these high energy particles strike other materials – which is already happening near the black hole – gamma rays and high-energy neutrinos are created. And just because TXS 0506 + 056 is a blazar, these neutrinos can end up in the Earth Ice detector.
Or was it just a coincidence?
"The age of multi-messenger astrophysics gives us a better understanding of the Universe," said France Córdova, director of the National Science Foundation, and the discovery was only possible. using different measuring instruments that measure different types of radiation and neutrinos.
Multi-messenger astrophysics was first used in 2017 when gravitational measurements combined with data of the telescope allowed two neutron stars to be observed for the first time., "Such breakthroughs are only possible through long-term fundamental research and the necessary investments in excellent research facilities". declared Córdova
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Although the joy of the success of the a search is great, there are also skeptical voices: is not it because the coincidence of neutrino measurement and telescope observations was only a coincidence? Could not this neutrino have a completely different origin and not come from TXS 0506 + 056? IceCube researchers used complicated statistical badyzes to calculate the probability of their discovery.
The physicist Anna Franckowiak of Desy in Zeuthen near Berlin made these calculations. She found that the measure of September 22, 2017 was only a coincidence with a probability of one thousandth. This is not enough for a scientific discovery
"Messengers of the Universe of High Energy"
In the same issue of "Science", however, researchers report in another article the subsequent evaluation previous IceCube measurements. Thus, from September 2014 to March 2015, they found more than a dozen neutrinos coming from the direction of TXS 0506 + 056, although they were not as energetic as the neutrino's September 2017.
Franckowiak anticipates that here the probability of outliers statistics is one in 5000. Up to now, there are indications that black hole accelerators are sources of cosmic rays and high energy neutrinos in the center of active galaxies.
The IceCube consortium is made up of some 300 scientists from 12 countries led by the NSF. The biggest European partner is the Desy. In addition, nine German universities are involved in the research project. Professor Klaus Helbig from the University of Wuppertal is the spokesman for the German IceCube network. He looks forward to opening a new window of space research: "Cosmic neutrinos are messengers of the high energy universe."
How can neutrinos arise?
Part of cosmic radiation may be responsible. "It could be about half of the cosmic rays generated by this mechanism," says Elisa Resconi
That even in supernova explosions neutrinos can occur, you know it since 1987. At that time, the 1987A supernova exploded. In Japan, the Kamiokande detector was able to record some of the resulting neutrinos. "If a comparable supernova happened today," Resconi notes, "then the IceCube detector would record hundreds of thousands of neutrinos."
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The fusion of neutron stars could lead to particle acceleration and the next stage of neutrino formation. For example, an IceCube researcher, Marek Kowalski from Desy to Zeuthen, hopes that someday such a cosmic event will measure gravitational waves and neutrinos at the same time. This combination of multi-messenger astronomy has not been successful here yet.
The experimental evidence that neutrinos are also produced in such cosmic events is still pending. Elisa Resconi believes that IceCube neutrinos could be recorded by a fusion of two neutron stars if the event takes place close enough to Earth. The fusion of neutron stars, observed in 2017 with gravitational wave detectors, has gone too far. "If the distance was only a tenth," said Resconi, "we could probably watch that with IceCube too."
The second generation is already planned
The biggest challenge in neutrino research remains the difficulty of measuring the volatiles. Franckowiak, a researcher on IceCube, explains that of the 10,000 cosmic neutrinos that cross the detector in the Antarctic ice, only one can be detected. In order to open up new possibilities for research on neutrinos, an expansion of the detector, ie the installation of additional light sensors, would be necessary.
In fact, the construction of IceCube Gen.2 is already planned. The start of construction is planned for 2022. The new detector could be finished in 2030. It should be installed again the same amount of sensors. However, measurement accuracy will be four to five times better than today – as researchers have now determined better detector geometry.
The construction of the current IceCube detector cost 300 million euros. The second generation would cost about as much. What new ideas could the much more sensitive system offer? This question is in the stars.
