Dark matter is the term used by astronomers to describe matter that can not be seen, but whose affects have been observed. This has been primarily observed in the gravitational density of galaxies, which does not correlate with the number of observed stars. There are several theories as to what dark matter may be. One theory is that it is just known types of matter (like brown dwarfs, which are not very luminous stars) that are hard to detect; another theory is that it may be a completely unknown, undiscovered type of matter.
Instructions
-
-
1
Observe the gravitational density of a galaxy. This is accomplished by observing the velocity of stars around the galaxy's disk.
-
2
Estimate the mass of the galaxy based on observable stars. Gravitational density is directly related to overall mass.
-
-
3
Recognize that the observable mass is not enough to cause the gravitational density, and thus there must be a large amount of unobservable mass -- "dark matter."