Dark Matter

Dark Matter

Dark Matter Andrew Bilbrey Honors Physical Science Mr. Crupi 9/17/97 I'll be the first one to admit it. Dark mater is a boring subject. But until we can all grasp the meaning of quantum physics and what our universe is made of, we will never understand ourselves. This is what dark matter is all about; what scientists have been mystified about for the past few years. Many questions have come up in the study of this puzzling matter, but maybe we should start out with the basics. The Basics All throughout history, astronomers knew that there was matter that we couldn't see. The reason we cannot see it is because: 1. It doesn't emit any light, and 2. It doesn't emit any radio waves. The reason we know that there is matter we can't see is because of a few things. The one which we will be discussing at the moment is that the only thing that makes galaxies move is other galaxies gravitational pull. Scientists have noticed the galaxies inside of clusters over the years, and have perceived that to gain the speeds that the galaxies have been traveling, they would have to have much more, about 10 times more, mass to be moving at the speed they were moving. The more mass a galaxy has, the faster it will fling other galaxies, because of its gravity. In addition to the other facts, there is stronger evidence about mass in single galaxies, as opposed to clusters. This is called Rotation Curves. If you can find the rotation velocities of a galaxy, you can "weigh the galaxy". But how do you weigh the galaxy or the universe for that matter? We're about to find out. How Much Dark Matter You actually can weigh the universe with an actual measurement. A measurement that is almost inconceivable. This is called an "Omega". This might be a little confusing, but to explain an Omega you must think of infinity. A universe that is "closed", or so big that is eventually collapses into itself, has an Omega more than 1. On the other hand an "open" universe or a universe that expands forever is an Omega less than 1. Then there is a flat universe that is balanced in the middle of the two just stated, and is equal to an Omega of 1. The amount of matter that is visible in the universe is about Omega .05, and this would make the universe .95 dark matter. More realistically the universe is Omega .4, so that would mean that dark matter takes up .35 of our universe. What It Is Well, the first thing that probably comes to your mind is planets. Well, this could have a few bugs in it. For example, if you took all of the planets in our solar system, you would have less than .01 of the sun's mass. Therefore, if you took all the planets in the universe, it would logically make up about .005 of our universe. So there is still roughly 90% of the universe to account for. There is also a little bit of a problem and an answer in something called the Big Bang Nucleosynthesis, or BNN. Supposedly, when the Big Bang occurred the universe was a "hot soup" p.1 of What might dark matter be. Then when it all cooled, it formed ordinary matter like atoms, the most predominant atoms being helium and hydrogen. The amount of atoms that form, count on the amount of ordinary atom-forming material, called Baryons, there is. Another thing is the matter or brown dwarfs, white dwarfs, and jupiters. White dwarfs are stars that have almost burned out and appear to be white, brown dwarfs are massive objects that aren't big enough to start burning, and jupiters that are smaller objects that might burn if they were a few times bigger they already are*. There is also the case of exotic matter. This kind of matter doesn't really live up to its name because it really isn't exotic at all, but really means matter that isn't protons, neutrons, or electrons. There is also matter called neutrinos that has a significant part in dark matter. They are a particle known to exist, and is currently thought to be massless, but if an atom has weight, then particles that make atoms probably has weight, too. But even if the neutrinos of the universe had a small mass of 92 eV, or one five thousandth of the mass of an electron, it would be enough to make it Omega = 1. There are two other kinds of matter that are significant in our quest for dark matter. They are WIMPs and MACHOs. WIMP stands for Weakly Interacting Massive Particles, and MACHO stands for Massive Compact Halo Objects. WIMPs are matter that interacts weakly with the matter around it. And MACHOs can act as a lens to make things appear bigger than they really are. For example, say that a star that an astronomer has been observing for quite sometime now, suddenly becomes really big and much brighter, then going back to it's original form. The proposed reason for this is that a piece of Dark matter (specifically a MACHO) went between the object and the telescopes, bending the light and making it seam bigger and brighter. Something else to consider are the changes to gravity. Something that we can't readily understand, but it is a possibility that gravity might act differently than we know it in the case of galaxies. Conclusion While there is still so much to learn about the mystery of dark matter, I hope that I have helped you understand more about it. I know it can be a little confusing, but this is our universe, and the more we know, the better off we are. Beyley, S. "A Heavenly Host." Newsweek. V.127 Jan. 29 1996: p.52-53 Cowen, R. "Shedding Light On Our Galaxies Dark Matter." Science News. V.149 February 1996: p.77 Cook, W. J. "Stellar News For Stars and Dreamers." News & Work. V.120 Jan. 29 1996 p.67-68 Dursi, Jonathon. "The Evidence for Dark Matter." Http://astro.queensu.ca/~dursi/dm.1 Spring 1997 Dursi, Jonathon. "Stronger Evidence." Http://astro.queensu.ca/~dursi/dm.2 Spring 1997 Dursi, Jonathon. "How Much Dark Matter?" Http://astro.queensu.ca/~dursi/dm.3 Spring 1997 Dursi, Jonathon. "What Is It?" Http://astro.queensu.ca/~dursi/dm.4 Spring 1997 Dursi, Jonathon. "How Can We Tell?" Http://astro.queensu.ca/~dursi/dm.5 Spring 1997 Kondo, Yoji "Dark Matter." Microsoft Encarta 97 Encyclopedia v. 1997 Andrew Bilbrey Honors Physical Science Mr. Crupi 9/17/97 I'll be the first one to admit it. Dark mater is a boring subject. But until we can all grasp the meaning of quantum physics and what our universe is made of, we will never understand ourselves. This is what dark matter is all about; what scientists have been mystified about for the past few years. Many questions have come up in the study of this puzzling matter, but maybe we should start out with the basics. The Basics All throughout history, astronomers knew that there was matter that we couldn't see. The reason we cannot see it is because: