What is Dark Matter Made Of?

[Biologik]

Dark matter, is it composed of...

How can we be sure dark matter is matter, if it is, is it composed of Atoms? I thought if something was composed of Atoms it had to react to a magnetic field, which astrophysicists say it does not. Does it have a gravitational effect on other masses? Please post a detailed reply, but no to detailed. I'm only 13. (sorry if this may be grounds for infraction I really don't know what is)

 

[mathman]

Dark matter is best described by what it is not. For starters, it is NOT composed of atoms or anything that makes up atoms (protons, neutrons, electrons, etc.). It's existence is based ONLY on gravitational effects on a large scale - holding galaxies or galactic clusters together. These effects have been observed in sufficient detail that astronomers can describe its distribution in space. The big unanswered question is - what is it made of?