LYNETTE COOK / SCIENCE PHOTO LIBRARY LYNETTE COOK / SCIENCE PHOTO LIBRARY
Quasar. Artwork of a quasar (top right) with near- by galaxies & gas clouds casting shadows from its bright light. Quasars are probably massive black holes that have large amounts of material falling into them. This material heats up and glows as it falls, making the quasar many billions of times brighter than a normal star. Their light is Doppler red-shifted due to their speed away from us. All quasars are very distant which means, because of the finite speed of light, that they must have formed in the early universe. Gas atoms in inter- stellar clouds block only certain frequencies of light. By studying the quasar's light, the composition of the early universe can be measured.
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