Chapter 2: Dark Matter

Dark matter, its something we’ve probably all heard of but never understood…that’s all right, no one does. It was discovered when astronomers were looking into the various types of energies that galaxies, as a whole, possessed. When observed, galaxies had kinetic, spring and potential energy in one form or another. These energies can be measured but after many trials and results that simply didn’t make sense, scientists concluded that the total amount of mass in the galaxy could not be accounted for visually, therefore there was matter that we could not see. However, this unseen matter was not because of the fact that we are too far away to see it, it was because it is invisible. This leads into the most interesting point within the chapter that explains how dark matter influences the speed at which objects, like stars, move around the center of galaxies.This movement, alters the energy within a galaxy. Hammond explains how the farther away a star is in relation to the center of the galaxy, the slower it travels. Upon reading this I made the connection to our centripetal force lab, as the radius became smaller, the velocity increased; the same outcome applies in this case. For instance, in relation to our solar system, if you were to speed up the rotation of the planets around the sun by 7603200 times, it would take Mercury 1 second to orbit around the sun while it would take Pluto 20 minutes. To connect this to dark matter, you must fist understand some of it other characteristics. Scientists have concluded that the density of dark matter decreases inversely as it gets farther away from the center of the galaxy. The reason is unknown but again because it is just a theory, these characteristics must be given for the system to work and be somewhat understood. Another characteristic associated with dark matter is that it has gravity just like any other type of matter. Scientists have come to the conclusion that there are possibly two types of dark matter, hot and cold. They were given this name because hot is associated with more energy, and cold less. An example of a hot type of dark matter would be a black hole and an example of cold dark matter would be a neutrino (a very small, neutral particle that doesn’t react very much with mass). Its an interesting idea but NASA has found more proof, based on previous understandings, that dark matter can exist. They concluded that light bends around large objects, like galaxies. The amount of bend, however, is directly related to the mass of the object, or gravitational force. A galaxy, though big, wouldn’t have enough gravitational force or energy from the planets to do this to the extent that we observe. This means that there has to be some sort of unseen matter that influences this phenomenon and dark matter provides that solution. Its an interesting thought that some sort of dark matter, in this case cold, can be passing through us at this very second and that it can bend light. Dark matter is everywhere in the universe and, according to the idea, it is the most plentiful type of matter in the universe.