Astroparticle physics

Astroparticle physics, also called particle astrophysics, is a branch of particle physics that studies elementary particles of astronomical origin and their relation to astrophysics and cosmology. It is a relatively new field of research emerging at the intersection of particle physics, astronomy, astrophysics, detector physics, relativity, solid state physics, and cosmology. Partly motivated by the discovery of neutrino oscillation, the field has undergone rapid development, both theoretically and experimentally, since the early 2000s.

The field of astroparticle physics is evolved out of optical astronomy. With the growth of detector technology came the more mature astrophysics, which involved multiple physics subtopics, such as mechanics, electrodynamics, thermodynamics, plasma physics, nuclear physics, relativity, and particle physics. Particle physicists found astrophysics necessary due to difficulty in producing particles with comparable energy to those found in space. For example, the cosmic ray spectrum contains particles with energies as high as 10²⁰ eV, where a proton-proton collision at the Large Hadron Collider occurs at an energy of ~10¹² eV.

The field can be said to have begun in 1910, when a German physicist named Theodor Wulf measured the ionization in the air, an indicator of gamma radiation, at the bottom and top of the Eiffel Tower. He found that there was far more ionization at the top than what was expected if only terrestrial sources were attributed for this radiation.

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