The 'ghost particles' that bombard the Earth
The ‘ghost particles’ that bombard the Earth

For the first time in history, a team of astronomers has found the source of a  high-energy cosmic neutrino from outside our galaxy. The so-called ‘ghost particles’ detected in Antarctica on September 22, 2017, reveals that, traveled 4 billion light years to reach us and that this particle came from a blazar, a spiral galaxy with a massive black hole in its center that rotates at high speed: an extremely energetic object. Thus, apparently, apart from neutrinos, gamma rays are produced partially by high-energy protons in the jets of supermassive black holes like this blazar.

It is a surprising discovery, which not only confirms Blazar as a source of high-energy neutrinos, but also establishes a new field of study: multi-messenger neutrino astrophysics: the use of different types of detectors gathered to study the same phenomenon. This same technique was used in the incredible research that confirmed and photographed neutron stars in collision.

Neutrinos from outside the galaxy

High-energy extragalactic neutrinos have been an enigmatic puzzle since their first detection in 2012, identified with the specialized IceCube neutrino detector at the South Pole, taking advantage of Antarctic ice. Subatomic particles are rare, but they are not much more rare than neutrinos. Their mass is almost zero, they travel almost at the speed of light, and do not really interact with normal matter; for them, the universe would be almost disembodied. Hence the name ‘ghost particle’.

However, that does not mean that they can not interact with the matter and this is where the IceCube observatory of Antarctica comes in, since from time to time, a neutrino can interact with the ice and create a flash of light.

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The scientists detected neutrinos from a 1987 supernova in the galactic halo of the Milky Way (sn1987a) with energy of up to 36 megaelectronvolts. The 2012 neutrinos also far outweighed any close comparison: the neutrino energy was 300 teraelectronvolts, more than 100 million times more energetic or about 20 times more than the LHC, the most powerful particle accelerator in the world.

Bearing in mind that for neutrinos, the rest of the universe does not really exist, they always travel in a straight line. And that’s how the experts discovered where this little subatomic particle came from.

The origin, a blazar 4,000 million light years away called TXS 0506 + 056, right next to Orion, a finding that illustrates that the associated high-energy cosmic rays consisting mainly of protons and atomic nuclei also come from the same place .

There are several thousand of these highly energetic objects known in the sky; but they had been quite low on the list as possible sources of high- energy neutrinos.

“It’s interesting to see how there was a general consensus in the astrophysical community that blazars are probably not sources of cosmic rays, and here we are,” said University of Wisconsin-Madison physicist Francis Halzen and lead scientist at the IceCube Neutrino Observatory. 

The finding was supported by observations from two gamma-ray telescopes: the Fermi Gamma-ray Space Telescope in orbit from NASA and the Cherenkov Telescope (MAGIC) in the Canary Islands. Both detected a flash of gamma-ray activity of high energy from TXS 0506 + 056.

“All the pieces fit together”, concluded the physicist of UW-Madison Albrecht Karle and co-author of the work published by Science. “The neutrino flare in our archival data became independent confirmation, and together with observations from other observatories, it is convincing evidence that this blazar is a source of extremely energetic neutrinos and, therefore, high-energy cosmic rays. Energy”.

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