Astronomy Jargon 101: Cosmic Strings

In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll do a little dance about today’s topic: cosmic strings!

What if I told you that there might be relics from the ancient universe roaming the cosmos? Demons from another age that could slice the Earth in two?

No, it’s not the setting for a new fantasy series, it’s just…physics.

The early, early, early universe was a pretty crazy time. Temperatures were high, pressures were high, densities were high. Things were so intense that physics itself was different. The four forces of nature were fused into a single, unified force (we think). As the universe expanded and cooled, the forces split off from each other.

But that splitting may not have happened very smoothly. As the universe underwent those radical phase transitions, regions of space may have been caught, trapped between two different pockets of transition. Those regions would evolve to become folds in space itself, the cosmic strings.

We’re not sure if cosmic strings exist. If they do, they likely have the width of a proton but could stretch from one end of the observable universe to the other. They would be so dense that a mile of string-stuff would outweigh the Earth.

And they would vibrate. Ripples can race down their lengths at the speed of light. They can fold in on themselves and pinch off, creating loops that eventually vibrate themselves to oblivion.

We’re not even sure what it would be like to encounter a cosmic string, because we’re not sure how the strings would interact with the other forces and particles in the universe.

We can try to find cosmic strings by looking for double images. Because of their extreme gravity, they split the path of light from background objects, causing those background objects to appear duplicated. But so far all searches have come up dry.

That’s a bit of a problem, because cosmic strings come up pretty generically in our models of the early universe, so they should be out there, somewhere. And so the search continues.