Particle Acceleration

The Universe is awash in highly energetic particles with velocities approaching the speed of light. Though these particles, collectively known as cosmic rays, exist in many places throughout the Universe  — and can even be found slamming into our own atmosphere — scientists don’t yet fully understand their origins.

Certain cosmic phenomena can impart particles with energies exceeding the capability of the best accelerators on Earth by a factor of a thousand or more. We know this because subatomic particles have been detected with as much energy as a well-hit baseball! Known as cosmic rays, these high-energy particles are capable of reaching Earth, where they are studied either by satellite-based detectors like the Fermi Gamma-ray Space Telescope or from the ground with Cherenkov telescopes like H.E.S.S. and VERITAS, instruments that examine interactions between the rays and the Earth’s atmosphere. 

Though scientists have developed phenomenological models to explain the behavior of these particles, the mechanisms that underlie their acceleration are not fully understood. Scientists speculate, however, that explosions of massive stars, known as supernovae, and the resulting shock waves sent into the surrounding interstellar gas could be one source of the motive force. There is also an emerging consensus that magnetic fields play a role in helping these particles achieve their enormous energies. However, magnetic fields can also mask the origin of charged particles by pulling them off their original course. To determine the origins of cosmic rays, scientists look at neutral particles like neutrinos, which propagate in straight lines from their sources. High-energy neutrinos have been detected from supernova explosions, bolstering that origin theory.

Scientists face significant challenges in seeking to identify and understand the sources of these highly energetic particles. The equations describing the acceleration and propagation of cosmic rays are extremely complex and observations require precise instruments such as Fermi. Eventually, scientists may be able to use the data from Fermi and other instruments to better understand these particles.

Motivated by the rich data supplied by Fermi, KIPAC researchers are pursuing an understanding of the phenomena responsible for the acceleration of particles to enormous energies. To expand their view of the Universe, KIPAC scientists are conducting radio, X-ray, and optical observations of celestial gamma-ray sources. KIPAC’s search runs the gamut from the exotic — remnants of exploded stars and astrophysical jets — to the seemingly mundane — our own Sun. Magnetohydrodynamic processes associated with solar flares can produce so-called coronal mass ejections, which bombard the inner solar system with cosmic rays.. On occasion, disturbances these cause in the geomagnetic field of the Earth, and can even disrupt electrical transmission lines.