Particle Acceleration

particle acceleration

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

Nature’s High-Performance Accelerators

Celestial objects such as neutron stars are the remnants of exploded stars. They can eject particles with energies exceeding the capability of the best accelerators on Earth by a factor of a thousand or more. 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 (Fermi), or from the ground with Cerenkov telescopes like HESS and VERITAS, instruments that examine interaction between the rays and the Earth’s atmosphere. 

Though scientists have developed provisional 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 may provide the motive force. There is also 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 in supernova explosions, bolstering that origin theory.

Understanding Natural Particle Acceleration Sources

Scientists face significant challenges in seeking to identify and understand the sources of these highly energetic particles. The equations describing them are highly 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 and build more powerful and efficient accelerators to replicate them on Earth.

Motivated by the rich data supplied by Fermi, KIPAC researchers are vigorously 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 busy planning and 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. Once thought to be an ordinary and quite stable star, the Sun is now known to contain very energetic particles. On occasion these particles penetrate the Earth's atmosphere, and can even briefly disrupt transmission of radio and TV signals.

Developing Simulations

Researchers at KIPAC are also engaged in studying the implications of these phenomena based on the analysis of data from various ground- and space-based observatories. Much of this work involves constructing detailed numerical simulations. These simulations suggest that shocks from stellar explosions compress the surrounding matter and ambient magnetic fields. Based on this research, KIPAC researchers have also concluded that magnetic fields are responsible for the collimated jets—straight and narrow flows of energy and matter—emanating from the centers of many galaxies.