Dark Matter

Dark matter is believed be five times more abundant than normal matter. Dark matter was first suspected when astronomers observed that galaxies possessed more mass than the stars could account for, the velocities of the stars should have overcome gravitational forces and those star would have escaped into the void of space. Currently, scientists have ruled out any normal matter as possible dark matter candidates. Researchers believe that in the early universe, when it was very hot and turbulent, dark matter interacted with normal particles more so than it does now. During that time, it was thought dark matter would have been easily detectable through
their interactions with normal matter.

Just like protons and neutrons are comprised of quarks, scientists believe that dark matter is also comprised of 'stealth' particles. Supercomputer analysis suggests that these particles would have masses ~200x10^12 eV, which is way more massive than known elementary particles. These stealth particles are believed to be held together by another mysterious 'dark form' strong interaction. Once the universe cooled, these particles are thought to have developed some sort of new weak interaction with ordinary matter. Experiments at the Large Hadron Collider are seeking out to rule out or detect any instances of dark matter interactions with ordinary particles.

The lower image shows the proposed distribution of dark matter extrapolated from observations in gravitational lensing.


Source: http://www.space.com/31013-stealth-dark-matter-universe-missing-mass.html