Researcher Q&A FAQ-Cosmic Rays

These questions have been answered by the scientists who are part of the Ask a High-Energy Astronmer program.

Why do we study cosmic rays? I understand that they might come form exploding stars, but why do we study them and for what purpose would it serve?

We study cosmic rays because they are one of our few samples of matter from outside the solar system. Studying the composition of cosmic rays tells us how the galaxy has continued to evolve chemically since the solar system was formed. This helps us to understand how the solar system got the chemical composition that it has, and so tells us about our origin. Studying how cosmic rays have gotten to us tells us about the dynamics of the Milky Way galaxy. Also, historically, many new particles (muons and pions for example) were discovered first in the cosmic rays.

For more information on cosmic rays, you can check the Cosmic and Heliospheric Learning Center at:

Thanks for your questions

Eric Christian
for Ask a High-Energy Astronomer

Could you tell me who created antimatter, and who first studied it?

Antiparticles are just a set of sub-atomic particles with some properties opposite to those of another set of particles with which we are more familiar. For example, the positron is the antiparticle equivalent of the electron. When a particle and its antiparticle meet, they annihilate with the release of a lot of energy.

Antiparticles will have been produced in the big bang which initiated the universe. In fact, most models of the big bang produce as much antimatter as ordinary matter, which is not easy to reconcile with the largely matter universe we see around us. Antiparticles are also produced in the transformation and interaction of other particles. For instance, a proton can sometimes produce a neutron and a positron.

The English physicist Paul Dirac first proposed the existence of antiparticles, when he derived equations which had solutions corresponding to both normal and antimatter particles. The American physicist Carl Anderson made the first detection of antimatter when looking at cosmic ray tracks in 1932 and noting that some tracks bent the 'wrong way' in a magnetic field.

Paul Butterworth
for the Ask a High-Energy Astronomer team

I am currently doing a research paper involving cosmic rays. My question is what are the effects of cosmic radiation to other stellar bodies? Or do stellar bodies affect the behavior of cosmic rays? How do cosmic particles get accelerated to speeds almost the speed of light?

Cosmic rays generally have little effect on other stellar bodies. The energy absorbed from a cosmic ray may be re-emitted at a lower energy, but the effect is usually small.

Stellar bodies affect the trajectories of cosmic rays primarily through their magnetic fields. However, the overall magnetic field of the interstellar medium is generally more important.

The acceleration mechanism in one of the key issues in the study of cosmic rays. It is generally believed that cosmic rays are accelerated in the shocks which accompany supernova explosions. Recent evidence for this has been detected in ROSAT data of the supernova remnant SN1006. The paper describing this result appeared in the journal Nature in 1995 (the full reference is Koyama et al, Nature, 1995 vol 378, pp. 255-258). Cosmic rays may also be accelerated by the strong magnetic fields associated with pulsars.

For further discussion about cosmic rays, you might also check the book "High Energy Astrophysics" by Malcom S. Longair (2nd Edition, 1992, Cambridge). Volume 2 contains a discussion of acceleration mechanisms. You may likely find articles at more of a lay person level in back issues of Sky and Telescope or Scientific American.

I hope this is helpful.

Jim Lochner
for Imagine the Universe!

Is it possible that the primary cause of ozone depletion are cosmic rays as it enters the atmosphere? And the big "hole" of the ozone layer at Antarctica is the result of the geomagnetic effect on cosmic rays, even though they are isotropic?

The ozone layer is the result of an equilibrium between the creation and destruction of ozone by UV light (UV creates ozone by ionizing free oxygen atoms which then combine with oxygen molecules to create ozone). Cosmic rays have been studied since the 1930s and we have no reason to believe that cosmic rays have not always existed. So if cosmic rays destroyed ozone at a significant level, then there would be no ozone layer (or at least a layer significantly smaller than the UV-only interaction picture would predict). More specifically, cosmic rays are made up of high energy particles and photons, which only react well with free electrons and dense material with high atomic numbers (note that high-Z atoms have a lot of electrons which are effectively "free" given the high energy of the cosmic rays). So in order for cosmic rays to have been significant in the creation of ozone holes, the flux of cosmic rays would have had to have increased by orders of magnitude, which has not occurred (to my knowledge).

Andy Ptak
for the Ask a High-Energy Astronomer team