The Dark Matter Mystery

During the last few decades, astronomers have discovered that most of the material in the Universe is invisible -- impossible to see with a telescope since it does not interact with light. Such material is called dark matter, and scientists have no ideas as to what it is. About 80% of the mass of a galaxy consists of this mysterious material. It was detected through its gravitational effects -- it causes the stars in the outer regions of a galaxy to orbit faster than expected: They travel more rapidly than they would if galaxies consisted only of the stars, planets, dust and gas that astronomers can observe with telescopes and other astronomical instruments. The dark matter also seems to be present in clusters of galaxies in even greater concentrations. During the evolution of the Universe, the dark matter helped material to clump together through gravity to produce the galaxies and the galaxy clusters. It is embarrassing that we are living in a Universe in which we do not know 95% of its contents. This is the greatest unsolved problem in astronomy and is known as the mystery of dark matter.

     Dark matter determines the ultimate fate of the Universe. The Universe is currently expanding, that is, the very fabric of space is stretching thereby causing distant galaxies to move away from one another. If a lot of dark matter is present, then its gravitation pull will eventually cause the expansion to cease. Then, space would collapse upon itself drawing all the galaxies together in a tremendous implosion called the Big Crunch. The situation would be similar to the Big Bang but in reverse. The Universe would heat up and become full of light and radiation. If not too much dark matter is present, then the Universe will continue its expansion forever. Galaxies would become separated by enormous distances and the Universe would cool to frigid temperatures. Eventually, all stars would burn out and the Universe would become cold and black. Thus, the world will end in fire or the world will end ice as Robert Frost has so succinctly put it in his poem. The amount of dark matter in the Universe determines which of these two possibilities will occur.

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