Sunday, December 12, 2010
Dark matter is pretty much THE most complex and difficult to understand thing that I have learned recently. Dark matter, to put it blankly, is not normal matter. There are no protons, neutrons, or electrons. It is an inferred idea because of strange gravitational pulls that have manifested themselves, but not their sources. It was hypothesized to make up for the discrepancies between measurements of the mass of galaxies, cluster galaxies, and the entire universe made through dynamical and general relativistic means, and measurements based on the mass of visible "luminous" matter that these objects contain. According to Friedmann equations,72% of the universe is dark energy, 23% of the mass-energy density of the observable universe is dark matter, and 4.6% makes up the ordinary matter. Thus, 80% of the entire observable universe is dark matter, and only 20% is normal matter. The idea of dark matter was created when a man by the name of Fritz Zwicky observed "missing mass" in the orbital velocities of galaxies in clusters. The difference of dark matter and normal matter is the fact that dark matter is not made up of atoms and such, but rather is made up of neutrinos, axions, and supersymmetrical particles. Scientists have used gravitational lensing to see that light has been bent at places where there wasn't any grouping of visible matter. There are three kinds of dark matter. Cold, warm, and hot dark matter. Cold dark matter is particles moving at classical velocities. Warm matter is particles moving at relativistic speeds. And hot matter is particles moving at ultrarelativistic speeds. Fritz then went on to try and observe this dark matter at work. He applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. Fritz estimated the cluster's total mass based on the motions of galaxies near its edge and compared that to one based on the number of galaxies and total brightness of the cluster. He found that there was about 400 times more estimated mass than was actually visible. And this is where I'm stumped so far, because I'm still trying to figure out the equation of the shape of galaxies which is quite difficult to understand at the moment. So if you want to add anything that I left out besides the fact that dark matter is invisible because it doesn't reflect light, then go ahead and post.