Home South pole ice ‘Neutrino factories’ may hold the answer to the cosmic ray mystery

‘Neutrino factories’ may hold the answer to the cosmic ray mystery

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New research has revealed that the high-energy neutrinos and cosmic rays that bombard Earth from deep space come from blazars – actively galactic nuclei (AGNs) that lurk at the center of galaxies and are powered by supermassive black holes. .

Researchers know that cosmic rays are charged particles from deep space that continuously strike the Earth with energies as high as 1020 electron-volts – a million times more energetic than the energies generated at the Large Hadron Collider (LHC). What could launch these particles with such force that they travel billions of light-years, however, remains a mystery.

This is because cosmic rays are made up of electrically charged particles, which means that as they travel billions of light-years from their source to Earth, they are repeatedly deflected by the magnetic fields of galaxies, making their sources impossible to spot.

Related: High-energy ‘ghost particle’ traced to distant galaxy in astronomy breakthrough

Some of the processes and events that launch cosmic rays also emit astrophysical neutrinos, and these “ghost” particles could be used as “messengers” to solve this puzzle, according to a team of astrophysicists.

“Astrophysical neutrinos are produced exclusively in processes involving the acceleration of cosmic rays,” said Sara Buson, team member and Julius-Maximilians-Universität (JMU) Würzburg Professor of Astrophysics. A declaration. (opens in a new tab)

Neutrinos are chargeless, low-mass particles that interact so weakly with matter that they pass through galaxies, planets, and even the human body almost without a trace. Because they have no charge, neutrinos don’t experience the same deflections as cosmic rays, which means their sources can be located more precisely.

In 2017, a neutrino signal was detected that could be traced back to blazar TXS 0506+056. Accordingly, Buson suggested that blazars – which emit more radiation than the entire stellar population of the galaxies around them – are responsible for emitting high-energy neutrinos.

This image taken by NASA’s Wide-field Infrared Survey Explorer (WISE) shows a blazar – a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed directly at Earth. (Image credit: NASA/JPL-Caltech/Kavli)

In 2021, she and her team set out to cement this link with a multi-messenger astronomy project, which mixes “mainstream” astronomy with neutrino observations. These new results were obtained using data from the IceCube Neutrino observatory – the most sensitive neutrino detector ever created – located deep under the ice of Antarctica’s south pole.

The team used this data to confirm that the location of blazars matched the direction of astrophysical neutrinos often enough that this association could not be attributed to chance alone, providing the first strong evidence for the link between astrophysical neutrinos and blazars. .

“After several rolls of the dice, we found that the random association can only exceed that of the real data once in a million trials,” said Andrea Tramacere, a member of the team and a scientist in the department of astronomy from the University of Geneva. “This is solid proof that our associations are correct.”

And because these neutrinos are created in sites where cosmic rays are accelerated and launched, this indicates that blazars are also responsible for accelerating cosmic rays. This could be the result of the way the supermassive black hole at the heart of a blazar “chews up” matter like gas and dust that surrounds them before it is “fed” – or accreted – to their surface.

The spinning of black holes that drag the very fabric of spacetime with them, an effect called frame drag or Lense-Thirring precession, ensures that matter around them cannot stay still, facilitating acceleration. particles.

“The process of accretion and rotation of the black hole leads to the formation of relativistic jets, where the particles are accelerated and emit radiation up to energies of trillions [times higher than] that of visible light,” Tramacere explained. “Discovering the connection between these objects and cosmic rays could be the ‘Rosetta Stone’ of high-energy astrophysics.”

According to Tramacere, the next step in this research is to study the difference between the types of blazars that emit neutrinos and those that do not.

“This will help us understand to what extent the environment and the accelerator ‘talk’ to each other,” said the scientist from the University of Geneva. “We can then eliminate some models, improve the predictive power of others, and finally add more pieces to the eternal puzzle of cosmic ray acceleration.”

The team’s findings were published in the journal Letters from the Astrophysical Journal. (opens in a new tab)