What is a 'cosmic string'?
Super strings are what physicists consider the 'end of the line' in describing the structure of both particles and fields in nature. There typical sizes are believed to be near 10^-33 centimeters, although some recent proposals suggest that these strings can be a lot bigger. String theory is the current theory which looks like it might be able to describe, in one consistent language, how all of the particles and fields we know about, work, and blend together to form the physical world and all of its laws and 'symmetries'. It will explain why he have gravity, why the electron has the mass it does, and why the electron/proton mass ratio is 1/1864, among many other things.
Cosmic strings are another thing entirely.
When the universe was inflating after the Big Bang, the field that caused this rapid inflation 'crystalized' so that space-itself became a patina of stringy discontinuities and other patterns. Its hard to describe this, but when you look at the surface of a pond, you see plates of ice grow until they collide with their neighbors, and you get these patterns on the ice that look like lines. When 3-d space cooled, some cosmologists think that space also took-on a texture which consists of lines ( strings) and other kinds of 'textures'. When matter cooled to form galaxies, it tended to fall into these stringy boundaries too. They are called Cosmic Strings, but they have nothing to do with Super Strings.
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