Astronomy and Astrophysics in the New Millennium (2001) / Chapter Skim
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Appendix: Definitions
Appendix: Definitions
Pages 213-228
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Append~x- Dein~t~ons
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The ultimate energy source for active galaxies may be the accretion of matter onto a supermassive black hole. Active galaxies can emit strongly across the entire electromagnetic spectrum, from radio waves to gamma rays.
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Black hole A region in space where the density of matter is so extreme, and the resultant pull of gravity so strong, that not even light can escape. Black holes are probably the end point in the evolution of some types of stars and are probably located at the centers of some active galaxies and quasars.
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Cosmic microwave background radiation The radiation left over from the Big Bang explosion at the beginning of the universe. As the universe expanded, the temperature of the fireball cooled to its present level of 2.7 degrees above absolute zero (2.7 K)
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Most astronomical observations measure some form of electromagnetic radiation. Expansion of the universe The tendency of every part of the universe to move away from every other part due to the initial impetus of the Big Bang; also known as the Hubble expansion, after the American astronomer Edwin Hubble, whose observations of receding galaxies led to scientists' current understanding of the expanding universe.
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Infrared astronomy The study of astronomical objects using intermediate-wavelength radiation to which the atmosphere is mostly opaque and the human eye insensitive. Humans sense infrared energy as heat.
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Optical astronomy The study of astronomical objects using light waves with wavelengths from about 1 to 0.3 ,um. The human eye is sensitive to most of these wavelengths.
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Active galaxies are probably less luminous and less distant versions of quasars. Radio astronomy The study of astronomical objects using radio waves with wavelengths generally longer than 0.5 to 1 mm.
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Supermassive black hole A black hole that is much more massive than the Sun. Supermassive black holes with masses exceeding a million solar masses are found in the nuclei of most galaxies.
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ATNF Australia Telescope National Facility. The main national organization supporting and undertaking research in radio astronomy.
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CGRO The Compton Gamma Ray Observatory. A telescope launched in 1991 to study highly energetic gamma rays from astronomical sources.
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GSMT The Giant Segmented Mirror Telescope, a 30-m-class, groundbased telescope. HALCA An 8-m radio telescope satellite and the key component of Japan's VLBI Space Observatory Program.
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MAXIMA Millimeter Anisotropy experiment Imaging Array, a balloonborne millimeter-wave telescope designed to measure the angular power spectrum of fluctuations in the CMB over a wide range of angular scales. MERLIN The Multi-Element Radio Linked Interferometer Network, an array of radio telescopes distributed around Great Britain and operated by the Jodrell Bank Observatory.
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SIRTF The Space Infrared Telescope Facility. NASA's fourth Great Observatory will study infrared radiation.
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ULDB NASA's Ultralong-Duration Balloon program. VERITAS The Very Energetic Radiation Imaging Telescope Array System, designed to study energetic gamma rays using ground-based telescopes.
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