An artist's impression of the cascading particle showers created by cosmic rays striking Earth's atmosphere. (Image Credit: Simon Swordy/University of Chicago/NASA)
Cosmic rays are particles—principally the nuclei of atoms, electrons and in rare instances, antimatter—moving at extremely high speed through the universe. The particles strike and shatter gas molecules in Earth's atmosphere, generating cascades of "secondary" subatomic particles and radiation known as air showers. These showers can reach all the way to the ground, where detectors on can help scientists reconstruct the properties of the original cosmic ray. Telescopes in space can also detect cosmic rays indirectly by observing the gamma rays created when cosmic ray particles collide with interstellar gas and dust. The astrophysical sources of cosmic rays have long been debated. Supernovae, the explosions of stars, have recently been confirmed as significant contributors to the cosmic ray bombardment of Earth. Another suspected origin for cosmic rays are supermassive black holes in the cores of galaxies. The gravity of these massive objects accelerates and smashes matter together, giving off huge amounts of energy in phenomena called active galactic nuclei. Cosmic rays are not dangerous to people on Earth's surface, though their air showers of radiation do contribute to small upticks in cancer.
Norbert Schulz and Nicola Omodei discuss the recent detection of a dying star igniting the most powerful blast ever seen – something so powerful it radiated energy that was 500 million times that of visible light and how scientists have discovered that a familiar sight in the skies is actually our earliest view yet of a star being consumed by the remnant of a nearby exploded star.
On Thursday, Feb. 28, 12:00-12:30pm PDT, science writer Bruce Lieberman will ask your questions about the new data on cosmic rays in an interview with Stefan Funk, Assistant Professor of Physics, Stanford University, and member, KIPAC.
In southeastern Colorado, a land better known for crops and livestock may soon host the world's largest astrophysical detector. If an international consortium of scientists gets a green light from funding agencies, it will build an array for detecting cosmic rays.