Dark Matter essays

Dark Matter essays 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 universes matter does not radiate it provides no glow that we can detect in the electromagnetic spectrum. Now in the 21st century, Zwicky and Oorts theories have been further enhanced. We have already observed in clusters of galaxies that the motion of galaxies within a cluster suggests that they are bound by a total gravitational force due to about 5-10 times as much matter as can be accounted for from luminous matter in said galaxies. But it is also theorized that within an individual galaxy, you can measure the rate of rotation of the stars about the galactic center of rotation. The resultant rotation curve is simply related to the distribution of matter in the galaxy. The outer stars in the galaxies seem to rotate too fast fo...