THE FIRST BLACK HOLES

Since just after the Big Bang, ancient black holes may have been shaping the Universe as we know it. Now, scientists are tantalisingly close to glimpsing these mysterious objects

- COLIN STUART

Out there among the stars lies a hidden swarm of black holes. They have been around ever since the dawn of time, quietly and not so subtly influencing the evolution of the Universe.

Without them there would be no stars, no planets and no life to marvel at the Universe’s wonders. Now, for the very first time, we may finally have the tools to find them.

Black holes are one of astronomy’s most famous objects. Their gravity is so extreme that escape is impossible if you venture too close. There are different sizes of black holes, but they are normally gargantuan monsters considerably more massive than our own Sun. They usually remain hidden from view because no light can escape to reveal them to us. Yet we have seen them, thanks to gravitational wave detectors like LIGO and VIRGO that have detected signals from colliding black holes. We’ve never been more confident that these cosmic trapdoors exist.

However, there is one type of black hole that still remains theoretical, one that could solve a long-standing cosmological conundrum to boot.

Immediately after the Big Bang there were small fluctuations in the new Universe’s density – regions that had slightly more or less mass than the average. Where the mass was above the norm, material could have collapsed to form mini black holes. As they’ve been around for pretty much as long as the Universe itself, these black holes are called ‘primordial’ black holes.

According to theoretical models, primordial black holes can have a wide range of masses. They could be lighter than an eyelash or heavier than a star. So far we’ve been able to rule out some masses through observations, opening up two possible mass ranges or ‘windows’ for primordial black holes.