Dark Matter

A detailed Summary of Dark Matter


Two people have been credited for determining the need for dark matter. The first was astronomer Jan Oort, who back in 1932 measured the perpendicular motions of nearby stars relative to the disk of our galaxy. By studying the gravitational influence of the disk on these stars he was able to calculate the mass of the disk. The value he determined was twice as much as that inferred by the visible stars and nebulae in that region. A year later in 1933 astronomer Fritz Zwicky estimated the mass of a group of galaxies by measuring their brightness. When Zwicky used a different method of calculating the mass of the cluster he found it to be 400 times the value from directly inferring the mass from the brightness of the cluster. In both cases Oort and Zxwicky came to the conclusion that the visible galaxies only accounted for 10% of the mass needed to keep them gravitationally in the cluster.

Based on 70 years of accumulated observations of the motions of galaxies and the expansion of the universe, most astronomers believe that as much as 90% of the stuff constituting the universe may be objects or particles that cannot be seen. In other words, most of the universe's matter does not radiate - it provides no glow that we c


The second theory group for dark matter are called Weakly Interactive Massive Particles (WIMPs). Particle physicists theorize that WIMPs are tiny non-baryonic particles that usually only interact with baryonic particles gravitationally. Therefore they would pass through normal matter. The problem with detecting WIMPs is that they rarely interact with normal matter other than gravitationally. In order for WIMPs to be a plausible candidate for the explanation of dark matter there must be millions of WIMPs passing through normal matter every few seconds. MACHO's are sought after by astronomers, and WIMPs by physicists. But most astronomers would agree that MACHOs alone do not make up enough accountable mass.

From NASA's Hubble telescope, astronomers have been able to estimate that red dwarfs comprise of only 6% of the mass making up galactic halo matter. Another way of detecting dark matter halo objects is by observing a phenomenon called Gravitational Lensing. It occurs when a red dwarf or black hole passes between a star or galaxy and an observer on Earth. The MACHO focuses the light rays due to the MACHOs high gravitational field causing the light source to appear brighter to the observer. This effect was actually proven by Einstein in 1919.

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Category: Science

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