Re: What is 'exotic radiation'?

"Exotic radiation" is not really an official scientific designation of a
specific type or class of radiation.

The term is used in science fiction
to denote a mysterious radiation when an actual scientific explanation is
not available.  Notable uses are the "McKay and Mrs. Miller" episode of the
science fiction show Stargate Atlantis and in the movie "The Fantastic Four."  

In the realm of real science, the term "exotic radiation" would generally
refer to radiation of exotic particles or normal light produced in any
particularly unusual fashion.  The term has been used to describe unusual
occurrences of Smith-Purcell radiation, for example, produced when
high-speed electrons travel through a crystal or other regular structure
(the periodic variation in electric and magnetic fields within the crystal
causes the electron to wiggle as it flies by, producing ordinary radio
waves or microwaves).  X-rays from extreme magnetic field of unusual
objects like magnetar stars have occasionally been dubbed exotic radiation,
though the x-rays themselves are not unusual.  What's exotic is the star
itself, or the spectrum of radiation produced (if it is non-thermal due to
the massive magnetic field).  

A more accurate usage would probably be to refer to high-energy exotic
particles, which typically have very short lifetimes (hence they are exotic
in that they would disappear in nature).  These particles are produced by
high-energy cosmic rays, solar flares (though these don't typically live
long enough to reach the Earth), or particle accelerators and are typically
only observed because their velocities (near the speed of light) cause a
relativistic time dilation. At these speeds, the particles take far longer
to decay into more ordinary particles.  A massive zoo of such particles can
be created in high-energy particle collisions.

Another more accurate usage for the term "exotic particles" could be to
refer to particles whose properties have been predicted by theoretical
physicists but have not yet been observed.  Tachyons are a favorite to
borrow from science fiction, a tachyon is a particle which always travels
faster than the speed of light.  Another are WIMPS (weakly interacting
massive particles), which may comprise much of the dark matter which causes
galaxies to rotate faster than gravitation from the ordinary matter within
them can explain.  WIMPS would only interact with ordinary matter very
weakly, hence the reason they have never been observed.