By studying the Universe across the spectrum we can get a more complete understanding of objects in space. The light from each part of the electromagnetic spectrum brings us valuable and unique information. X-rays and gamma rays bring us information about high energy phenomena such as black holes, supernova remnants, hot gas, and neutron stars. Ultraviolet light reveals hot stars and quasars while visible light shows us warmer stars, planets, nebulae, and galaxies. In the infrared we see cool stars, regions of starbirth, cool dusty regions of space, and the core of our galaxy. Radiation in the radio region shows us cold molecular clouds and the radiation left over from the Big Bang.
All astronomical objects, except for black holes, emit at least some light. Many objects emit more radiation in some parts of the electromagnetic spectrum than in others, while others emit strongly across the entire spectrum. Each part of the spectrum reveals information not found at other wavelengths.
About The ImagesLet's take a multiwavelength look at some objects in space. As you view the next several pages, you may notice that the quality of the images, which depends on their resolution (or ability to see small details), is not the same for all of the pictures. This is because a variety of telescopes and detectors are used. In general, future telescopes always have better sensitivity and better resolution, and so the quality of images continually improves.
Also, different color scales are used in the images. Some of the visible light images as well as all of the non-visible light images are shown in false-color. A false-color image is one in which the colors are not the "true colors" of the object. Visible light colors are assigned to certain wavelength or intensity ranges so that we can see them with our eyes. To make an infrared image, for example, an electronic detector maps the infrared radiation intensity within its field of view. Those intensities can then be mapped into visible colors such as red, blue, yellow, and green.
As you compare these images, keep in mind that each picture tells us something different. Just as importantly, if we omitted any of the images, we would lose the information available to us in that portion of the spectrum.
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