The distant galaxy fires fast neutrinos to the earth

The earth is regularly bombarded with fast particles – called neutrinos – coming from a distant galaxy. This concludes an international team of hundreds of scientists Friday in Science. Only one neutrino tracked them down. The discovery confirms that the most energy-rich cosmic radiation comes from outside the Milky Way. "For the first time, a high-energy neutrino has been observed," says Heino Falcke, professor of astroparticle physics at Radboud University. He was not involved in the research: "It's one of the most important discoveries of 2018."

"Neutrino astronomy has become a reality," says Professor Nick van Eijndhoven, IceCube Program Manager at Vrije Universiteit Brussel. His team was closely involved in setting up the alarm system, which has already alarmed several observatories and satellites 45 seconds after detection.

Neutrinos are subatomic particles that attract almost nothing from matter as we know it. They are related to the electron, but have no electric charge and virtually no mass. Without our knowledge, every innumerable second of these particles passes through us every second. They do not address the damage: we are looking for them.

Almost four billion years ago, a colossal explosion of energy took place in the heart of a distant galaxy. During this event, in addition to the electromagnetic radiation of various wavelengths, energy-rich neutrinos were emitted at a speed close to that of light

On September 22, 2017, a swarm of these particles almost elusive, reached the South Pole. In addition, one of them collided with a molecule of water, which caused a brief flash of blue light and ultraviolet light.

The flash was recorded with "IceCube", a neutrino detector consisting of more than 5,000 light sensors that are sunk at depths of 1,450 to 2,450 meters into the Antarctic ice. IceCube detects about 200 neutrinos a day, but most of them do not come from far away. They appear in clashes between cosmic rays – charged particles of space – and atoms and molecules in the earth 's atmosphere.

From time to time, however, there is between them a neutrino which clearly has more energy than the others. These "high energy" neutrinos must come from a lot further. IceCube was built specifically for the detection of these relatively rare particles. This has given 82 hits since 2013 – averaging about one per month

The neutrino that was detected in September last year was notable for its extremely high energy, which was about 300 tera-electronvolts in technical terms. In an absolute sense it is very little: not even a millionth joule, while to make a cup of tea it takes 80,000 Joules. But for a neutrino, it's exceptional.

High energy neutrinos can occur only in extreme cases. In a collision between two neutron stars, for example, or a super-heavy black hole that engulfs large quantities of matter. In both cases, two "jets" directed in opposite directions appear: beams of high energy electromagnetic radiation and subatomic particles.

To find out what was the source of the neutrino in September 2017, you need to know which direction it came from. IceCube itself can give an indication about this, but not enough to indicate a specific object. This is why, with such a special detection, many observatories and space telescopes are automatically reported to observe striking phenomena in the area of ​​the sky concerned.

A few hours later, scientists from the American / European space telescope Fermi report that the indicated location coincides almost exactly. with a well-known source of gamma radiation – the most energy-rich form of electromagnetic radiation. That was quasar TXS 0506 + 056, a huge elliptical galaxy with a super heavy black hole in its core that is busy engulfing the matter from its surroundings.

Follow-up observations with other telescopes have shown that TXS 0506 + 056 was not only a source of energy-rich neutrinos and rays gamma but also X-rays, visible light and radio radiation. In addition, an IceCube data analysis showed that at the end of 2014 or early 2015, some 13 lower energy neutrinos also came from the same direction. It's as good as certain that TXS 0506 + 056 occasionally pulls neutrinos in our direction.

It is the same as the link with the issue of "cosmic radiation" – the collective name for high energy particles that continually rain down on the earth. About the exact origin of these particles, which account for about 90% of protons, there is still a lot of uncertainty. This is because protons are charged particles that are deflected by magnetic fields. As a result, they continually deviate from their line during their journey through space, making it impossible to trace their origin.

Neutrinos do not have this drawback: they move in a straight line. If active galaxies such as TXS 0506 + 056 are clearly a source of energy-rich neutrinos, then it is very likely that they are also important producers of "ordinary" cosmic radiation.

"In particle physics, people usually induce neutrinos and gamma rays by accelerating the protons," says Falcke. "And the big question was whether something similar can happen in space.We see the protons coming to earth, but we had never seen an accelerator." This uncertainty has now been raised: TXS 0506 + 056 behaves like a particle accelerator in the space.

"This is not a big surprise to me, but it's a good thing that the link was finally found after 20 years of research, "says Falcke." It was really one of the main goals of experiments like IceCube. "