09/28/2005
Cosmic Fastballs
I may have mentioned previously the time in my youth when I was knocked out, not by a punch but by a baseball. I was tossing a ball back and forth with one of our high school’s pitchers when he threw me an unexpected curveball that tipped my undersized catcher’s mitt and hit me right between the eyes. If you missed the story, I was carried across the street to a friend’s yard where I awakened and later went home, not telling my mother of the incident. The next morning, I had two beautiful black eyes and my secret was exposed.
I recalled this experience when I read a statement by Kitta MacPherson in an article under her byline in the September 23 Star-Ledger. The statement mentioned “microscopic rays, each of which pack the energy of a pitched fastball …” Her “rays” were cosmic rays that bombard our Earth even as we speak. On reading MacPherson’s statement, I thought, “Hey, if I was knocked out by a curveball, I’d really be decked by a fastball!” Was Kitta was off base in her calculation? I calculated the kinetic energy of a 5-ounce baseball traveling 100 miles an hour and came up with roughly 140 joules. (If you’re not familiar with joules, it’s one of many units of energy. Don’t worry; we’ll only use it as a reference number.)
I then went to NASA’s and other Web sites to find out what the energies of cosmic rays are and found that some have energies as high as 16 joules. I calculated that’s more like a knuckleball at 35 miles an hour, still fast enough to get your attention if it hits you between the eyes. After this calculation, I stumbled upon an article on cosmic rays written for the MacMillan Encyclopedia of Physics by R. A. Mewaldt of the California Institute of Technology. Kitta MacPherson may have seen the same article. Mewaldt mentions that the highest energy cosmic rays (more than 16 joules) have energies equivalent to the kinetic energy of a baseball traveling at approximately 100 miles per hour. I won’t argue with a fellow from Cal Tech.
What are cosmic rays? Where do they come from? The answer to the first question is easy. Cosmic rays were discovered in 1912 by Victor Hess, a fellow who went up in a balloon and found that the background radiation went up as he went up. At the time, it was thought that this radiation was electromagnetic similar to radio waves or X-rays; hence the term cosmic rays. Today, cosmic rays consist of more than just “rays”. There are X-rays and gamma rays in the mix but most interesting here are the charged particles that carry all that energy.
These particles are common elements such as hydrogen, helium, carbon, oxygen, nitrogen or practically any other element. The particles are charged because all the electrons have been stripped from the atoms, leaving positively charged nuclei behind. For example, about 89 percent of the cosmic particles are protons (the proton is the nucleus of the ordinary hydrogen atom) while 10 percent are helium nuclei. The remaining one percent are nuclei of other heavier elements. These particles are traveling very fast; hence their high energies.
The question as to where the cosmic rays come from has been the tough one. Our Sun erupts and spews out various types of stuff in addition to the heat and light that makes its way to our planet. However, the particles from the Sun don’t pack much energy compared to those “fastballs” that come from beyond our solar system. For almost a century, astronomers have been searching for the source of these high-energy particles. Other stars and the regions around black holes where material is being sucked in are possible sources, but the most popular suspect has been shockwaves associated with supernovae. The Star-Ledger article describes the work of Rutgers University researchers John Hughes, Jessica Warren and others that has yielded strong evidence that supernovae do spawn high-energy cosmic rays.
As a visiting scientist, I go down to Rutgers on the Busch campus in Piscataway. There, I pass a building topped with a small dome housing a telescope. I doubt that the Rutgers astronomers use that telescope. They have a much more exciting toy at their disposal, the orbiting Chandra X-ray telescope, still doing yeoman work out in space beyond its projected 5-year life. Hughes and his team report their latest work in an upcoming issue of The Astrophysical Journal. It deals with a supernova that has quite a history.
It was in 1572 that Tycho Brahe, a Danish astronomer, looked through his telescope and saw a “new” star in the constellation Cassiopeia. This bright new star turned out to be the explosion of an existing star and Tycho’s discovery exploded the prevailing belief that stars never change. He had discovered the first known supernova. As we’ve discussed before, when a star blows up it sheds its outer material and, depending on its size, the remaining material ends up being a white dwarf (our sun’s eventual fate), a neutron star or a black hole.
What about the stuff that blew off in the explosion? Today, over 400 years later, we can still see a smudge of light known as Tycho’s remnant, an expanding outward shock wave and the wave of debris from the 1572 explosion. The debris is moving outward at about 6 million miles an hour. (There’s also another shock wave moving inward into the debris.) Many have been observed and studied since 1572. In the case of Tycho’s remnant, the standard theory predicts that the outward moving shockwave should be about two light-years ahead of the wave of debris from the explosion. That’s about half the distance from our Sun to the nearest star.
Here’s where the Rutgers crew comes into the picture. They used Chandra to look at Tycho’s remnant and what they found does not agree with standard theory. Chandra tells them that, relatively speaking, the wave of debris from the 1572 explosion is keeping up much more closely with the outward shockwave. The debris is only about half a light-year behind the shockwave, not the predicted two light-years. That’s a big difference.
The shockwave is sort of like the shock wave generated by a jet airplane exceeding the speed of sound. The shock wave produces sharp changes in pressure and temperature in its wake. The fact that the debris is following so close to the outward shockwave is evidence that an appreciable amount of the energy in the shockwave is being used to speed up those particles in the debris wave. Some particles are speeded up more than others, even approaching the speed of light. Those little buggers might be among the “fastballs” heading our way.
These Chandra data are apparently the best evidence to date showing that are sources for high-energy cosmic particles. The Chandra results complement earlier work by an international team on a thousand-year-old supernova remnant. They used a combination of four telescopes termed HESS (High Energy Stereoscopic System) in Namibia in Africa to show that the shockwave in that remnant was accelerating gamma rays to very high energies. So, we have shockwaves speeding up both rays and particles from supernova.
Do we have to worry that we’re in danger of getting hit with an invisible ray or particle packing enough of a punch to do bodily harm? Obviously not, or we’d all be nursing bruises of unknown origin. Thankfully, our atmosphere does a great job of stopping these unseen missiles from outer space. If you’re still worried about getting hit with a real “fastball”, Mewaldt says that those super high-energy cosmic rays are pretty rare, roughly only 1 per square kilometer per century! I can live with that.
Allen F. Bortrum
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