Dark Matter - What Is It?
...found a discrepancy that suggests ninety percent of the universe is matter in a form that cannot be seen. (1). This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science. That it exists is one of the few things on which researchers have been certain. What is it, really? How do we know that it's there? How do we ¡°see¡± it if it's ¡°dark¡±?
Some scientists think dark matter is in the form of massive objects, such as black holes, that hang out around galaxies unseen. Other scientists believe dark matter to be subatomic particles that rarely interact with ordinary matter.
In 1933, the astronomer Fritz Zwicky while studying the motions of distant galaxies in the Coma cluster estimated the total mass of a group of galaxies by measuring their brightness. When he used a different method to compute the mass of the same cluster of galaxies, he came up with a number that was 400 times his original estimate (13). This discrepancy in the observed and computed masses is now known as "the missing mass problem. ¡° Nearly seventy years later his conclusion has been confirmed for many other galaxy clusters, and it is now generally believed that the most of the mass in the universe is in some dark form which has still only been detected through its gravitational effects.¡±(5)
What do scientists look for when they search for dark matter? Possibilities for dark matter range from tiny subatomic particles weighing 100,000 times less than an electron to black holes with masses millions of times that of the sun (7). The two main categories that scientists consider as possible candidates for dark matter have been dubbed MACHOs (Massive Astrophysical Compact Halo Objects), and WIMPs (Weakly Interacting Massive Particles). MACHOs are the big, strong dark matter objects ranging in size from small...
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