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Definition: Dark matter from Brewer's Dictionary of Modern Phrase and Fable

A term used by astronomers for material that has not been directly detected but whose existence is postulated to account for the motions of stars and galaxies. It is thought that some 90 per cent of the mass in the universe resides in some form of dark matter.

dark matter

From The Columbia Encyclopedia
material that is believed to make up nearly 27% of the mass of the universe but is not readily visible because it neither emits nor reflects electromagnetic radiation , such as light or radio signals. Its existence would explain gravitational anomalies seen in the motion and distribution of galaxies. Dark matter can be detected only indirectly, e.g., through the bending of light rays from distant stars by its gravity. Dark matter may consist of dust, planets, intergalactic gas formed of ordinary matter, or of MACHOs [ M assive A strophysical C ompact H alo O bjects], nonluminous bodies such as burned-out stars, black holes , and brown dwarfs ; these are the so-called hot dark matter and would be dispersed uniformly throughout the universe. The discovery in 2001 of a large concentration of white dwarf stars in the halo surrounding the Milky Way indicates that these burned-out stars could represent as much as a third of the dark matter in the universe. Other theories hold that it is made…
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Full text Article dark matter

From The Columbia Encyclopedia
material that is believed to make up nearly 27% of the mass of the universe but is not readily visible because it neither emits nor reflects electromagnetic radiation , such as light or radio signals. Its existence would explain gravitational anomalies seen in the motion and distribution of…
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Full text Article dark matter

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Hypothetical matter that, according to certain modern theories of cosmology , is thought to make up over 90% of the matter in the universe, and about 23% of the total mass (the rest of the mass being due to dark energy – a form of energy thought to cause the universe to expand at an accelerating…
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Full text Article DARK MATTER

From Gaither's Dictionary of Scientific Quotations
No biographical data available Considering that more than 90% of the universe consists of unknown dark matter, we may have to admit that the stellar system we have studied so long, and with so much success since the middle of the twentieth century, may add up to only a tiny part of the galaxy – as…
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Full text Article dark matter

From The American Heritage Student Science Dictionary
Matter that gives off little or no detectable radiation. Astronomers have proposed that dark matter exists because the amount of visible matter in the universe is not enough to generate the gravitational forces that are observed. dark matter What is the universe made of? We know that galaxies…
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Full text Article dark matter

From Science Encyclopedia: Encyclopedia of Space and Astronomy
Material in the universe that cannot be observed directly because it emits very little or no electromagnetic radiation, but whose gravitational effects can be measured and quantified. Dark matter was originally called missing mass and, as suggested by its name, was discovered only through its…
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Full text Article Dark matter

From 50 Physics Ideas You Really Need to Know Full text Article SPACE AND TIME
Dark matter
Ninety percent of the matter in the universe does not glow but is dark. Dark matter is detectable by its gravitational effect but hardly interacts with light waves or matter. Scientists think it may be in the form of MACHOs, failed stars and gaseous planets, or WIMPs, exotic subatomic particles – …
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Full text Article dark matter

From Collins Dictionary of Astronomy
Matter that probably comprises 75% (or more) of the mass of the Universe but is undetectable except by its gravitational effects. Dark matter was first suspected in clusters of galaxies when the galaxies were found to move with too high a speed to be retained in the cluster by their gravitational…
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Full text Article BLACK HOLES & DARK MATTER

From National Geographic Answer Book: 10,001 Fast Facts About Our World Full text Article THE UNIVERSE
TYPES OF BLACK HOLE STELLAR MASS Formed from collapsed cores of giant stars Mass a few times greater than that of Earth's sun INTERMEDIATE MASS 100-10,000 times more massive than Earth's sun Only a few identified and confirmed SUPERMASSIVE Largest type Inhabits cores of galaxies From a few million…
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The blue highlights surrounding the object Abell...
In the 1930s, astronomer Fritz Zwicky (1898–1974) noticed that, in the Coma cluster of galaxies, many of the individual galaxies were moving around so fast that there had to be a tremendous amount of gravitational pull toward the center of the cluster; otherwise, the galaxies would literally fling…
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Full text Article cold dark matter

From Astronomy Encyclopedia
Proposed as the missing mass component of galaxies. Flattened rotation curves of galaxies, and the velocities of stars at different distances from the centre of the galaxy, led astronomers to believe there was more mass present in the HALOES of galaxies than was being seen. Mass in the form of…
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