Jose J. Blanco-Pillado

A balloon doesn't deflate all at once: first, dents appear on its surface, which run, merge, and finally the balloon shrivels into a point. Domain walls behave in much the same way — thin partitions that divided space in the first moments after the Big Bang.

Pluck a guitar string, and it will vibrate and quickly fade. Now imagine a cosmic string: an ultra-thin filament of pure energy left over from the Big Bang, trillions of times thinner than an atom and denser than a neutron star. Strike it, and it might sing for billions of years.