C. Possibilities for Dark Matter

The three main categories of objects that scientists consider as possibilities for dark matter include MACHOs, WIMPs, and gas. The first two are acronyms which help us to remember what they represent. Listed below are the pros and cons for the likelihood that they might be a component of dark matter.

MACHOs (Massive Compact Halo Objects): MACHOs are the big, strong, dark matter objects ranging in size from small stars to super massive black holes. MACHOS are made of ordinary matter, which is called baryonic matter. Astronomers search for MACHOs. Examples: black holes, neutron stars, white dwarfs, brown dwarfs.

Neutron Stars and Black Holes are the final result of a supernova. They are both very massive stars. Neutron stars are 1.4 to 3 times the mass of the sun. Black holes are greater than 3 times the mass of the sun.

	Pros:	They both can be dark. However, black holes emit no light; they are truly black.
	Cons:	These objects occur less frequently than white dwarfs. As a result of a supernova, a release of a massive amount of energy and heavy elements should occur. However, there is no such evidence that they occur in sufficient numbers in the halo of galaxies.