Scientists Reveal 2 Million Black Hole Mergers Are Missed Every Year

This encompasses a lost 8 billion light years of universe evolution.
Loukia Papadopoulos

Dr Rory Smith from the ARC Centre of Excellence in Gravitational Wave Discovery at Monash University in Australia has an interesting fact to share with the world. It turns out that despite the great work he and his team have been doing, there is a chance that about 2 million gravitational wave events from merging black holes, "a pair of merging black holes every 200 seconds and a pair of merging neutron stars every 15 seconds" are missed by scientists.


How does Smith know this? Well, he and his colleagues, also at Monash University, have developed a method to detect the presence of these weak events. The method "means that we may be able to look more than 8 billion light-years further than we are currently observing," Smith said.

"This will give us a snapshot of what the early universe looked like while providing insights into the evolution of the universe."

Binary black hole mergers release huge amounts of energy in the form of gravitational waves. This makes them particularly adept at being routinely detected by the Advanced LIGO-Virgo detector network.

According to co-author, Eric Thrane from OzGrav-Monash, these gravitational waves "carry information about spacetime and nuclear matter in the most extreme environments in the Universe. Individual observations of gravitational waves trace the evolution of stars, star clusters, and galaxies."

"By piecing together information from many merger events, we can begin to understand the environments in which stars live and evolve, and what causes their eventual fate as black holes. The further away we see the gravitational waves from these mergers, the younger the Universe was when they formed. We can trace the evolution of stars and galaxies throughout cosmic time, back to when the Universe was a fraction of its current age," added Thrane.

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The researchers evaluate the population properties of binary black hole mergers. And since the vast majority of compact binary mergers produce gravitational waves that are too weak to produce clear detections, large amounts of information is currently being missed by our observatories.

"Moreover, inferences made about the black hole population may be susceptible to a 'selection bias' due to the fact that we only see a handful of the loudest, most nearby systems. Selection bias means we might only be getting a snapshot of black holes, rather than the full picture," Smith warned.