Astronomy is entering a new era with neutrinos - Le Figaro

The first high-energy neutrinos were finally detected after fifty years of research.

rumor rustled from the preliminary results presented in reduced committee last May. The first cosmic neutrinos, direct witnesses of the most energetic events in the Universe, were finally detected. It was nearly fifty years astrophysicists waiting for this news that the official announcement was made Friday Science . U.S. IceCube detector, 1 km3 of ice encased sensors buried 2 km depth beneath the South Pole, found 28 of these particles between 2010 and 2012.

“I think we will look in the future this article as a starting point for neutrino astronomy,” enthuses John Carr, director of research at CNRS Centre for Particle Physics of Marseilles and former head of program competitor Antares, a “neutrino telescope” thirty times smaller plummeted to 2500 m depth in the Mediterranean off the coast of Porquerolles.

They do not “see” the electrons

Detection of a high energy neutrino.

But what this new discipline? Classical astronomy is to look photons, that is to say the light at different wavelengths (visible range, of course, but also microwave, infrared, ultraviolet, X-rays and gamma). Problem: photons are easily absorbed by matter. They are struggling to escape from high-density areas such as galactic nuclei or the remnants of exploded stars (also called supernovae).

This is not the case of neutrinos. These hardly interact with matter. Since they do not “see” the electrons, they can only be stopped by the atomic nuclei. But if an atom was represented by a football field, the nucleus would be no bigger than a grain of sand. For these particles, the material is almost transparent. If a shade tissue enough to capture about half of the photons emitted by a light bulb, it would lead to a thickness of several billion miles to get the same effect with a dropping neutrinos!

“28 is both very low and very encouraging,”

This property allows neutrinos to make us unique astronomical information. But this advantage is also a disadvantage: the neutrinos are very difficult to find. However, their detection is not impossible. When it hit a core material, the neutrino emits a spray of particles, like a flash of light. This event happens hundreds of times a day in IceCube. However, most of these neutrinos come from the Sun or the disintegration of very high energy protons, called cosmic rays, when they hit the atmosphere.

But the challenge was to flush neutrino “created” thousands or billions of light years. The bet is successful. “28 is both very low and very encouraging notes Thierry Stolarczyk, astrophysicist at the CEA and former scientific director of the Antares project. These high-energy neutrinos carry with them important information about the extremely violent events that gave rise to them, “says the researcher. They could for example explain the exact nature of gamma-emission localized but colossal energy that lasts only a few tens of seconds.

“Charting the sky”

The IceCube sensors are located between 1500 and 2500 m depth.

accuracy and quantity of harvested by IceCube data are unfortunately not sufficient to help determine the exact origin of these few cosmic neutrinos. It seems that five of them come from the center of the Milky Way, but not absolute certainty.

“The aim is to draw up a chart of sources of these neutrinos, said John Carr. To do this, it would find thousands. “This would require many years and detectors 10 to 100 times larger. IceCube has already cost € 250 million, are billions that would be needed. Financing may be difficult to find. The future of neutrino astronomy is in.