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X-Rays - Another Form of LightLight can take on many forms. Radio waves, microwaves, infrared, visible, ultraviolet, X-ray and gamma radiation are all different forms of light. The energy of the photon tells what kind of light it is. Radio waves are composed of low energy photons. Optical photons--the only photons perceived by the human eye--are a million times more energetic than the typical radio photon. The energies of X-ray photons range from hundreds to thousands of times higher than that of optical photons. The speed of the particles when they collide or vibrate sets a limit on the energy of the photon. The speed is also a measure of temperature. (On a hot day, the particles in the air are moving faster than on a cold day.) Very low temperatures (hundreds of degrees below zero Celsius) produce low energy radio and microwave photons, whereas cool bodies like ours (about 30 degrees Celsius) produce infrared radiation. Very high temperatures (millions of degrees Celsius) produce X-rays.
The photons themselves can also collide with electrons. If the electrons have more energy than the photons, the collision can boost the energy of the photons. In this way, photons can be changed from low-energy photons to high-energy photons. This process, called Compton scattering, is thought to be important around black holes, where matter is dense and has been heated to many millions of degrees.
The photons collected in space by X-ray telescopes reveal the hot spots in the universe--regions where particles have been energized or raised to high temperatures by gigantic explosions or intense gravitational fields. Where do such conditions exist? In an astonishing variety of places, ranging from the vast spaces between galaxies to the bizarre, collapsed worlds of neutron stars and black holes. |
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Revised: August 29, 2006
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