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IN THE beginning, there was light. Then, perhaps, a point of darkness. More dark spots appeared, the light circling them before falling in like water down a drain. These would have been our universe’s first inhabitants, strange baby black holes gorging on the radiation that flooded out of the big bang. As the cosmos expanded and cooled, their feasting slowed.
Millions of years passed, some of the radiation that filled the cosmos giving way to matter, which eventually clumped together to form the first stars, planets and galaxies. Over time, some stars grew so large that when they ran out of fuel and collapsed, they turned into black holes themselves. But what happened to their distant ancestors from the dawn of time? Maybe those very first, primordial black holes faded away or perhaps they were big enough to survive to the present. Either way, they could help solve some of the biggest problems in cosmology. If they were ever there.
The concept of black holes, objects so enormously dense that not even light can escape their gravitational pull, has haunted cosmology for decades. Until recently, we had no direct evidence they existed. That changed in 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the aftershock of a pair of black holes colliding 1.3 billion light years away.
Experiments such as LIGO could be our best shot at finding evidence of primordial black holes too. In fact, some people think we have already spotted them. That would be a monumental discovery because these cosmic ancients wouldn’t only be our universe’s first black holes, but also its most interesting.
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