Astroparticle Physics revolves around phenomena that involve (astro)physics under the most extreme conditions.

Black holes with masses a billion times greater than the mass of the Sun, accelerate particles to velocities close to

the speed of light and display a variety of relativistic effects. The produced high-energy particles may be detected

on Earth and as such can provide us insight in the physical processes underlying these cataclysmic events.

This is just one example of this new exciting field of research, which combines the insights of Astrophysics,

Particle Physics and Cosmology.

As the leader of a group of scientists I am involved in a world wide effort to search for high-energy neutrinos

originating from cosmic phenomena.

For this we use the IceCube neutrino observatory, being the world's largest neutrino telescope at the South Pole.

Furthermore, I am also the project leader of the Radio Neutrino Observatory Greenland (RNO-G), that is currently

being deployed and which will address neutrino energies that are beyond the reach of IceCube.

This radio array will allow us to explore unknown territory at the very high energy end of the neutrino spectrum,

and search for the so called Cosmogenic Neutrinos (also known as GZK neutrinos) which are produced when

ultra-high energy nucleons are destroyed by interacting with the Cosmic Microwave Background photons.

Having no electrical charge and interacting only weakly with matter, neutrinos are special astronomical messengers.

Only they can carry information from violent cosmological events at the edge of the universe directly towards the Earth.

The advent of large scale Neutrino Observatories marks the birth of Neutrino Astronomy.

This field of research opens a completely new window on the Universe and as such is poised to yield new discoveries,

in a similar manner as with the introduction of Radio Astronomy.

The focus of my research is on transient phenomena, i.e. Gamma Ray Bursts (GRBs) and flares of Active Galactic Nuclei (AGN),

which are believed to be the most violent cosmic explosions, involving black holes and neutron stars, and the sources of

the most energetic Cosmic Rays.