The dramatic image of the nearby galaxy Centaurus A above, provides one of the best views of the effects of an active supermassive black hole to date. Opposing jets of high-energy particles can be seen extending to the outer reaches of the galaxy, and numerous smaller black holes in binary star systems are also visible. The image was obtained via an ultra-deep look at the galaxy with the Chandra X-Ray Observatory that was equivalent to more than seven days of continuous observations.

Centaurus A is the nearest galaxy to the Earth that contains a supermassive black hole actively powering a jet. A prominent X-ray jet extending for 13,000 light years points to the upper left in the image, with a shorter "counter-jet" aimed in the opposite direction. Astronomers think that such jets are important vehicles for transporting energy from the black hole to the much larger dimensions of a galaxy, and affecting the rate at which stars form there.

High-energy astrophysics

High-energy astrophysics involves the study of exceedingly dynamic and energetic phenomena occurring near the most extreme objects known to exist, such as black holes, neutron stars, white dwarfs, and supernova remnants.

These objects convert gravitational binding energy in the acceleration of extremely energetic particles called cosmic rays which have a non-thermal energy spectrum, spanning from 10¹⁰ eV (electron volts) all the way up to "ultrahigh energy cosmic rays" (UHECR), having energies on the order 10²⁰ eV (which, on average strike the Earth once per square kilometre per hundred years)

Almost 60 years after their first observation, the origin of high-energy cosmic rays is still unresolved. In the theoretical high energy astrophysics group at NTNU, we try to determine what the cosmic ray primaries are, where and what their sources are, and how the observed energy spectrum and clustering of arrival directions of cosmic rays can be explained.

A major obstacle for unveiling the sources of high-energy cosmic rays is their deflection in cosmic magnetic fields. A prerequisite for doing cosmic-ray astronomy is therefore a better knowledge of both the Galactic and the extragalactic magnetic fields. Another path is the "multi-messenger approach", i.e. the combination of data from cosmic-ray, neutrino, and gamma-ray experiments, that are becoming available now from new experiments like Auger Prime in Argentina,  the IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station, and the Cherenkov Telescope Array (CTA).

Since high-energy photons and neutrinos are produced as secondaries of hadronic interactions, their fluxes are intimately connected with the flux of cosmic rays. Hence, a combined interpretation of photons, neutrino, and cosmic-ray data will improve our understanding of the cosmic high-energy radiation.

Research areas

At NTNU, we are very active in different types of multi-messenger studies, ranging from trying to understand the origin of the diffuse cosmic-ray and neutrino emission to modelling the radiative and high-energy particle emission of individual astrophysical sources. We primarily focus on active galactic nuclei powered by a supermassive black hole with the latter approach, which requires using a combination of high-energy particle and multiwavelength astrophysical observations from radio and optical wavelengths through to X-rays and gamma-rays.

We also participate in the development of the science case and design of the next generation of photon, neutrino, and cosmic ray observatories which include the proposed  All-Sky Medium Energy Gamma-Ray Observatory (AMEGO), the  Global Cosmic Ray Observatory (GCOS), the Giant Radio Array for Neutrino Detection (GRAND), the Probe of Extreme Multi-Messenger Astrophysics (POEMMA), and a Planetary Neutrino Monitoring System (PLENuM).

Neutrino telescopes like IceCube also have the potential to measure unknown neutrino properties and interactions. For instance, neutrino telescopes are sensitive to the mass hierarchy and CP violation in the lepton sector.

Finally, we investigate possibilities to explain the observation of high cosmic rays with particle physics beyond the standard model or, conversely, to detect or to constrain new particles or interactions through cosmic-ray observations.