Monday, November 7, 2016

Shocks in the early universe could be detectable today

Physicists have discovered a surprising consequence of a widely supported model of the early universe: according to the model, tiny cosmological perturbations produced shocks in the radiation fluid just a fraction of a second after the big bang. These shocks would have collided with each other to generate gravitational waves that are large enough to be detected by today's gravitational wave detectors.

The physicists, Ue-Li Pen at the Canadian Institute for Theoretical Astrophysics in Toronto, and Neil Turok at the Perimeter Institute for Theoretical Physics in Waterloo, have published a paper on the shocks in the early universe and their aftermath in a recent issue of Physical Review Letters.

As the scientists explain, the most widely supported model of the early universe is one with a radiation-dominated background that is almost perfectly homogeneous, except for some tiny waves, or perturbations, in the radiation.

In the new study, Pen and Turok have theoretically shown that some of these early, tiny perturbations, which are small-amplitude waves, would have spiked to form large-amplitude waves, or shocks. These shocks would have formed only at very high temperatures, like those that occur immediately after the big bang.

The physicists also showed that, when two or more shocks collide with each other, they generate gravitational waves.
The results suggest that both colliding shocks and merging black holes—like those detected earlier this year by the LIGO experiment— contribute to the gravitational wave background.

Some researchers have previously speculated that the mergining black holes may have formed from the same perturbations that created the shocks and, further, that black holes of this size may make up the dark matter in our galaxy.

Source & further reading:

Image: Simulation showing cosmological initial conditions (left) evolving into shocks (right).
Credit: Pen and Turok 2016 American Physical Society

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