Dark Matter

Independent Study

Dominic Stelmach

Planetary Astronomy

David Maybury

December 3, 2015

Dark matter is one of the great mysteries in astronomy today, and although it is not viewable through telescopes, the hypothetical matter accounts for most of the matter in the universe; in fact, it is estimated that it constitutes 84.54 percent of all matter (Francis). It must then be understood as to how astronomers and physicists were able to arrive at such a conclusion, especially with no direct detection of dark matter as of yet. In fact, dark matter is undetectable at all wavelengths, from radio to gamma waves, and we only know of its existence due to its gravitational pull (597). Aside from this, however, there is little that is known about dark matter, and although many hypotheses have been suggested, none have been proven.

To help determine the existence of dark matter, many hypotheses have have been theorized, with its existence first postulated by Jan Oort in 1932 to account for the orbital velocities of the stars in the milky way, and then again in 1933 by Fritz Zwicky using the virial theorem. However, the first hypothesis to postulate dark matter based on robust evidence was formulated by Vera Robin and Kent Ford in the 60s, using galaxy rotation curves (Einasto). Following these past theories, many other observations have indicated the presence of dark matter through such means like gravitational lensing of background objects by galaxy clusters. This gravitational lensing essentially magnifies distant objects through galaxy clusters in between us and the distant object, thus being able to measure the total amount of matter. Comparing this with the hot gas viewed through X-ray is a big part of how we know that dark matter doesn’t collide with either itself or normal, atomic matter (Ethan).

Not only this, but the temperature distribution of hot gas in galaxy and galaxy clusters, particularly the Bullet Cluster (Ethan), have also helped to prove the existence of dark matter. The most recent, however, was the pattern of anisotropies in the cosmic microwave background, giving implications of small temperature fluctuations in the blackbody radiation left over from the Big Bang (Wright). However, even with this information and a general consensus among the science community, dark matter is still a hypothetical particle. There is still much that is needed to know, particularly a direct detection of the matter, to further proof of its existence. In fact, it is a simple understanding that dark matter is composed primarily of a not-yet characterized type of subatomic particle. With such little known about it, it can only be concluded that what is known is very minimal, and what great leaps some people have taken to explain it are only theories, not proven and sometimes not even provable.