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The Question
(Submitted May 26, 1997)
As a Radiographer for 14 years, I am familiar with how diagnostic
X-rays are produced by man. Other, than the obvious difference of
mechanical means of producing the X-rays that Dr. Roentgen discovered;
or even the radiation such as that noted at Chernobyl (please bear my
ignorance) are we talking a natural phenomena when you say High-Energy
Astrophysics--X-rays & gamma-rays or something other than the
mechanized means of production? By now, you see how little knowledge I
have of what is titled "High- Energy Astrophysics"...
The Answer
Yes, the X-rays we observe are natural -- not man made. They are
produced very far away in the myriad of phenomena described in
Imagine the Universe! (http://imagine.gsfc.nasa.gov/). The X-rays then
travel for hundreds to billions of years before they happen to hit the
detectors on our X-ray telescopes.
In fact there are two basic natural methods of producing
extraterrestrial X-ray -- thermal and non-thermal. Two members of our
ask_astro team replied to your message -- one describing the thermal
processes and the other the non-thermal processes. I have attached a
brief description of each with this E-mail (see below), and as I
mentioned above there is much information on this at our Web site.
Sincerely,
Jonathan Keohane and much of the Ask a High-Energy Astronomer
Team
Appendix A: Thermal X-rays (by Mike Arida)
At 37 C the human body emits infrared radiation. This is called blackbody radiation.
The hotter the object, the higher the energy of the photon's emitted.
When you heat a piece of metal in a fire till it glows read you have
energized some of those photons to the red part of the visible spectrum.
The sun, at 5,000 C emits most of its energy in the yellow/green part
of the visible spectrum.
A tungsten light bulb get to be about 10,000 C and emits in the
bluish/white end of the spectrum.
X-rays, being much more energetic than visible light, require a hotter source, in the 1 - 10's of millions of degree range. So one method of
X-ray production is in the very hot gas expanding outward after a
supernova explosion, or the gas heated as it spirals (and accelerates)
into a black hole.
Appendix B: Non-Thermal X-ray (by David Palmer)
Many X-rays studied by high-energy astronomers are produced by
high-energy electrons being accelerated or decelerated, either by being
deflected by a magnetic field, or by hitting other particles. X-ray
tubes used in radiography work the same way: a beam of electrons is
fired into a metal target, and as they stop the electrons produce
X-rays.
There are also gamma-rays produced by the decay of radioactive
isotopes. These are produced on Earth by reactors such as Chernobyl,
and in the sky by reactors such as novae and supernovae.
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