|
he universe is awash with relativistic charged particles, mostly ions, but including a distinctive electronic component, as well. Even under the protecting blanket of the earthıs magnetic field and atmosphere we are constantly bombarded with this natural "cosmic-rays" radiation. The most energetic particles, which can carry almost as much energy as a Nolan Ryan fastball, come from well outside the solar system. However, the sun, and even the earth, get into the act of producing the lowest energy cosmic-rays, which fill the famous van Allen Radiation Belts.
 |
| Pictured is a three dimensional simulation of a cosmic supersonic jet. The right image shows a volume rendering of shock waves formed inside the jet and in the cocoon it leaves behind. The left image illustrates the energetic properties of cosmic-ray electrons in this flow. Color patterns indicate the influence of shocks on the electron energies.
|
The higher energy cosmic-rays are thought mostly to be a byproduct of strong "collisionless" shock waves in tenuous cosmic plasmas. Shocks are central features in violent cosmic explosions, such as supernovas, but also in much more energetic phenomena, such as quasars, and even the gravitational collapse during formation of galaxies and clusters of galaxies throughout the history of the universe itself. The last of these shock waves are millions of light years across and may exist for billions of years.
Research over the past two decades has made it very clear that cosmic shocks, and the cosmic-rays they expel, are fundamental to a host of astrophysical issues. The cosmic-rays are important because they can absorb a significant fraction of the energy budget at a shock, while the energy distribution of the cosmic-rays provides a measure of the shock properties and offers an incisive probe of the physics of the collisionless shock waves themselves. The cosmic-rays emit light with distinctive properties so that they offer unique diagnostic possibilities for many cosmic phenomena. While these features are generally accepted,
 |
| Simulated radio and X-ray emission from the cosmic jet flow shown above, as it would be seen by a terrestrial astronomer. The right image corresponds to synchtrotron emission resulting from interactions betwen relativistic electrons and the local magnetic field, while the left image represents cosmic microwave background photons upscattered to X-ray energies by the same relativistic electrons.
|
they are poorly understood. Yet, their importance provides a strong incentive to develop comprehensive theories. The theoretical task is so complex, especially in application to real cosmic events, that sophisticated computational methods are absolutely essential for success.
|
| The simulated energy distribution of protons behind a collisionless shock wave showing the development of a high-energy "cosmic-ray tail" above the thermal distribution.
|
Supercomputing Institute Fellow Professor Thomas Jones of the Department of Astronomy at the University of Minnesota along with research associate and Supercomputing Institute Research Scholar Udo Gieseler, graduate students Francesco Miniati and Ian Tregillis, and Korean collaborators Professor Hyesung Kang of the Pusan National University and Professor Dongsu Ryu of the Chungnam National University have undertaken the task of developing and applying computational methods to overcome many of the biggest hurdles that must be overcome along the way. They have several linked efforts underway that have already born exciting fruit. It has been necessary to pioneer computational methods to model essential microphysics in collisionless shocked flows, high order methods to compute the dynamics of compressible, conducting fluids laced with dynamically significant magnetic fields, methods to transport relativistic charged particles in complex conducting plasma flows, and methods to compute the expected radiative emissions from the relativistic particles and simulate how the simulated cosmic structures would appear to an earth-bound observer. While there is still much work to be done in these areas, these researchers are now at the exciting stage where they can begin to challenge existing observational paradigms and make predictions about observations possible with the next generation of space observatories. Current efforts range from developing computational schemes to model the complex microphysics that "injects" thermal charged particles into the cosmic-ray population and incorporating "adaptive mesh refinement" techniques for the first time into numerical transport of cosmic-rays to simulating the observable properties of cosmic-rays expelled in supersonic plasma jets expelled from the centers of galaxies and cosmic-rays accelerated in the powerful shock waves stretching across and around giant clusters of galaxies.
|
|
This information is available in alternative formats upon request by
individuals with disabilities. Please send email to
alt-format@msi.umn.edu
or call 612-624-0528.
|
|
URL: http://
|
|
|
This page last modified on
|
|
Website related questions or problems should be directed to
webmaster@msi.umn.edu
The Supercomputing Institute does not collect personal information on
visitors to our website. For the University of Minnesota policy, see
www.privacy.umn.edu.
|
|
| |
