- Scientists develop a model that tries to solve the half-century-old enigma of origin of ultra-high particles in the universe.
- The model explains the origin of extreme-energy cosmic rays, high-energy gamma rays and high-energy neutrinos, and how these three cosmic particles are interconnected.
- The model links the origin of these particles with black-hole jets embedded in their environments.
In astroparticle physics, one of the biggest unsolved mystery has been the creation of extreme-energy cosmic rays, high-energy gamma rays and high-energy neutrinos.
Physicists at PennState and University of Maryland have come up with a new theoretical model that connects all these high-energy space particle with black hole jets embedded in their environments. All these space particles could be shot out into space after cosmic rays are accelerated by supermassive black holes’ jets.
Based on detailed numerical computations, the model explains why these 3 types of cosmic messenger particles have astonishingly similar power input into the universe, regardless of the fact that they’re observed by ground- and space-based detectors over ten orders of magnitude energy in individual particle.
It states that high-energy gamma rays and high-energy neutrinos are formed by particle collisions as cosmic rays’ daughter particles, and therefore can inherit the significant energy budget of their parent particles.
Energies Of These Three Cosmic Particles
The most energetic particles in the universe are ultrahigh-energy cosmic rays. Each of them has energy that’s too outrageous to be generated even by the world’s most powerful particle accelerator, the Large Hadron Collider.
The mysterious particles, Neutrinos rarely interact with matter. So far, high-energy neutrinos having one million MegaElectronVolts have been found in the IceCube Neutrino Observatory, Antarctica.
The highest electromagnetic energy has been observed in gamma rays. Such energies are over billion times stronger than a visible light’s photon observed by the Fermi Gamma-ray Space Telescope.
Physicists have combined all these data in numerical simulations to examine the fate of these charged particles.
In this new model, powerful jet of active galactic nuclei accelerate cosmic rays, which later escape through the radio lobes that are usually found at the jet’s end. They measure the propagation of cosmic ray as well as the interaction inside galaxy clusters in the presence of their surrounding magnetic field. Finally, they simulate this propagation and interaction data, integrating the contributions of all sources in the universe.
More specifically, the ultra-high energy cosmic-ray observation has revealed some characteristic features of extragalactic cosmic rays.
- The hardening in the spectrum of light particles is nearly 100 PeV.
- A transition from light to medium-heavy elements around 1019 eV is indicated by Auger data.
The direct calculations of indicators of the particle mass are consistent between different experiments, however, the interpretation of the ultrahigh-energy cosmic ray composition is still debated. These features were not taken into account in the simple convergence theory. The study provides a solid astrophysical model in which black hole jets embedded in bigger structures reconcile these observations.
Reference: Nature | doi:10.1038/s41567-017-0025-4 | PennState Science
One of the major suspects in this old puzzle of the formation of high-energy cosmic particle were ‘active galactic nuclei’ in galaxies that consists of extreme-radiating core region near the central supermassive black hole.
Some of the active galactic nuclei have enormous relativistic jets. High-energy cosmic particle produced by the jets are ejected into space at the speed of light.
This can explain the spectrum and composition of ultrahigh-energy cosmic rays. Also, it can account for unresolved phenomena found on ground-based experiments.
At the same time, one could explain high-energy neutrino spectrum over 100 million MegaElectronVolts through particle collisions between the gas in galaxy clusters and cosmic rays. Furthermore, the associated gamma-ray emission evolving from intergalactic space explains the mysterious part of the diffuse high-energy gamma-ray background, which is not associated with any specific kind of active galactic nucleus.
The model also tries to explain how these space particles are physically connected to each other by common mechanisms of high-energy gamma-ray and high-energy neutrino production. However, there are numerous new puzzles and other possibilities need to be uncovered, such as the neutrino data captured by IceCube Neutrino Observatory.
Hence, further studies based on multi-messenger mechanisms, combining information and theory with all 3 messenger data, are very important to test this new model.
The model is expected to be tested rigorously while observing with more advanced neutrino detectors like KM3Net, IceCube-Gen2, and the next generation Cherenkov Telescope Array and gamma-ray telescope. This will help us better understand the physics of high-energy cosmic particles, and our universe.