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