New research on the second biggest explosion after the Big Bang

A new study suggests that within a month of the Big Bang, a second explosion may have given the universe invisible dark matter.

The Big Bang may have been accompanied by a shadow, cosmologists have proposed in a new study, flooding our universe with mysterious dark matter . And we can see evidence for that event by studying ripples in the fabric of space-time.

Hubble Space Telescope image of the galaxy cluster Cl0024+1654, showing tiny red dots of stars against a field of blue dark matter.

After the Big Bang , most cosmologists believe that the universe underwent a period of rapid expansion, notably in its earliest moments, called inflation . No one knows what caused inflation, but it was necessary to explain various observations, such as the extreme geometric flatness of the universe at large scales.

Inflation was probably driven by some strange quantum field, a fundamental entity that pervades all of spacetime . At the end of inflation, that field decayed into a shower of particles and radiation, triggering the 'hot Big Bang' that physicists often associate with the beginning of the universe. Those particles would go on to combine into the first atoms when the universe was about 12 minutes old and — hundreds of millions of years later — begin to coalesce into stars and galaxies.

But there's another ingredient in the cosmic mix: dark matter. Again, cosmologists aren't sure what dark matter is, but they see evidence of its existence through its gravitational influence on regular matter.

Scientists have not seen evidence of dark matter's existence until much later in the universe's evolution, after the elusive substance had time to exert its gravitational influence, so it would not have necessarily filled the universe in a hot Big Bang along with the normal event. Plus, since dark matter doesn't interact with normal matter, it could have had its own dark Big Bang, the researchers claim.

Big Dark Bang

In their paper, the researchers explore what a dark Big Bang might look like. First, they hypothesize the existence of a new quantum field—a so-called 'dark field' —that would be needed to allow dark matter to form entirely independently.

In this new scenario, the dark Big Bang only occurred after inflation had died out and the universe expanded and cooled enough to force the dark field into its own phase transition, where it transformed itself into dark matter particles.

The researchers found that the Dark Big Bang must follow certain constraints. If it was too early, there would be too much dark matter today, and if it was too late, there would be too little. But if the Dark Big Bang occurred less than a month before the universe was formed, it could fit all known observations.

But most importantly, researchers have discovered that a dark Big Bang created a distinctive signature in gravitational waves, ripples in space-time that still travel around the universe today. That means the theory could one day be tested.