Cosmic String 

Thin loops of ultra dense engery, far narrower than the nucleus of an atom but stretching across vast distances, left over from the Big Bang and acting as gravitational 'seeds' on which the galaxies grew.

A piece of cosmic string just a mile long would weigh as much as the Earth. A cosmic string that stretched right across the universe could be scrunched up into a ball smaller than a single atom, but would weigh as much as a supercluster of galaxies.

Cosmic String by OneBadAsp October 21, 2006