6. Conclusion
6. Conclusion
Well, we hope we've shed a little light for you on dark matter. Remember that just because something cannot be seen doesn't mean it's not there. Dark matter is all around us in the universe, and there may even be dark matter passing through your body this second! We know that dark matter exists because we can observe its effects on other things in the universe; for example, by studying how fast galaxies orbit around each other, we can estimate how much extra dark matter there must be in the system in addition to all of the visible matter we can see. Scientists also study lengths and speeds of clusters of galaxies to determine how much dark matter must be there. A supercluster is a huge gathering of a bunch of smaller clusters of galaxies. Our own galaxy is called the Milky Way, but the supercluster that we belong to is called The Virgo Supercluster.
Matter is just stuff; it is anything that has mass. Now, remember that bowl of candy we showed you earlier? Of all the matter in the entire universe, almost all of it is dark matter that we can't see.
There are two main types of dark matter: baryonic dark matter and non-baryonic dark matter. Another way to say this is: dark matter made from atoms, and dark matter composed of some new strange particles which are not atoms. Since we don't exactly know what they are, one name given to these strange particles is "WIMPs" which stands for weakly interacting massive particles. This name means that they interact with regular matter only through gravitational forces, but they don't give off light or form chemical bonds with ordinary (atomic) matter. After the term "WIMP" was introduced to describe these strange particles, some scientists began to use the term "MACHOs" to describe a certain different type of dark atomic matter. MACHO stands for massive compact halo objects. MACHOS are much more massive than WIMPs. They are actually made of the same kind of atoms that make up everything you can see, though they are dark rather than visible. MACHOs include white dwarfs, brown dwarfs, and black holes. White dwarfs are old stars that have died and used up all their fuels. Brown dwarfs are very large objects that just aren't big enough to [start burning to produce their own late] burn fuel in their core and shine like a star. Black holes are regions in space where gravity is so strong that not even light can escape.
So, what is dark matter? It is "stuff" in the universe that has mass but gives off no light. Why is dark matter important? Most of the matter out there is in fact dark matter, so we can't understand what is in the universe without understanding dark matter. And, the amount of dark matter in the universe also helps determine the shape of the universe. How do we find dark matter? We observe its effects on other things.
Posted by hsutherl on April 24, 2005 at 12:49 AM