For the first time, physicists have revealed what the gravitational waves produced at the start of our Universe would have looked like.
Models show that signals from the ancient Universe, recorded just fractions of a second after the Big Bang, stand out as peaks against a broad background of gravitational wave signals and give astronomers a better idea of what they should be looking for in the cosmic record. If detected, these signals could reveal how our Universe looked moments after it first formed, and prove whether our current models of the Big Bang, and the evolution of the Universe, are correct.
Although gravitational waves were detected for the first time in a breakthrough experiment a year ago, Einstein first predicted their existence in 1916. The waves are ripples in the curvature of space-time that travel outward from their source. Every accelerating body produces these waves, but they are so faint that only those produced by extremely huge objects, like black holes and supernovae, are strong enough to be detected.
The researchers, from the University of Basel, Switzerland, wanted to study gravitational waves from the early Universe to learn more about a time when everything was compressed into a tiny space. In particular, they studied the “stochastic background” of gravitational waves. This is a combination of waves from a huge number of different sources that overlap and interfere with each other, like ripples on the surface of a lake when lots of rocks have been thrown in.
According to the Big Bang theory, fractions of a second after the event the Universe was incredibly dense, hot and small. "Picture something about the size of a football," Professor Stefan Antusch, lead author of the paper, explained.
It is thought at this moment, most of the football-sized Universe was made up of a particle called the inflaton. This formed clumps which began oscillating in localised regions of space. These regions are known as oscillons, and it is these regions from which the gravitational waves were produced.
"Although the oscillons have long since ceased to exist, the gravitational waves they emitted are omnipresent - and we can use them to look further into the past than ever before," says Antusch.
The team calculated the shape of the oscillons’ signals using computer models. The results showed the oscillons produced a peak in waves that should stand out compared to the broad range of frequencies produced by other gravitational wave sources.
"We would not have thought before our calculations that oscillons could produce such a strong signal at a specific frequency," Antusch said. This should make them easier to detect than we previously thought.
Now detectors will now be used to search for these peaks, to find whether these signals exist or not.
The calculations have been published in Physical Review Letters.