- Astrophysics, high-energy
The study of the universe as revealed by high-energy, invisible forms of light: x-rays and gamma rays. These
radiations are produced in the cosmos when gas is heated to millions of degrees Kelvin or electrons have
been accelerated to near the speed of light by violent and extreme conditions. Exploding stars, neutron stars,
black holes, and galaxy clusters, the most massive objects in the universe, are among the objects studied.
- Cosmology
The study of the structure and the origin of the universe, including the origin of galaxies, the elements, and matter itself.
When Albert Einstein proposed his theory of general relativity, the universe was believed to be static. Einstein had to modify
his equations so that general relativity would allow a static universe by adding a cosmological constant term. Today, this term
is incorporated into the current cosmological model.
- Dark Matter
Particles or objects that exert a gravitational force but do not emit any detectable light. Dark matter is the
dominant form of matter in our Galaxy. Astronomers have detected the presence of dark matter through its
gravitational effects and have shown that dark matter is not composed of ordinary atoms. Particle physicists
have suggested several plausible candidates for dark matter; planned experiments are capable of detecting
these new particles.
- Gravitational Lens
A massive body producing distorted, magnified, or multiple images of more distant objects when its
gravitational fields bend the paths of light rays. Lenses have been observed when the light from very distant
quasars is affected by intervening galaxies and clusters of galaxies, producing several different images of the
same quasar. A. Einstein predicted the occurrence of this phenomenon in 1936, but the discovery of real
gravitational lenses did not occur until 1979. Gravitational lenses, in addition to being intrinsically interesting,
can reveal the intrinsic properties of galaxies, active galaxies, and quasars, and provide information on the
universe and its contents, including dark matter.
- Weakly interacting massive particle (WIMP)
A hypothetical elementary particle that might make up most of the matter in the universe, and that is also
predicted to exist in supersymmetry theory. Most matter is detected only through its gravitational effects;
this “dark matter” has not been observed to emit, absorb, or reflect light of any wavelength. The total
amount of dark matter appears to be approximately ten times as great as all the ordinary matter in the
universe, and about one hundred times as great as all the visible matter. The nature of the dark matter is not
yet known, although many experiments are under way to try to discover it directly or indirectly.
Articles courtesy of Access Science
http://www.AccessScience.com
Copyright McGraw-Hill, all rights reserved.
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