Black holes can be hard to study since nothing escapes them, but astronomers can learn a lot by watching the the light around them and their gravitational waves. Over the years, researchers have observed many black holes end up pulling each other toward the same location where they eventually merge.

A new analysis that was conducted of data from the LIGO-Virgo-KAGRA collaboration, which took place in 2019, however finds that there may be a situation where three of them are coming together. Astronomer Wen-Biao Han of the Chinese Academy of Sciences reported:

“This is the first international discovery of clear evidence for a third compact object in a binary black hole merger event. It reveals that the binary black holes in GW190814 may not have formed in isolation but were part of a more complex gravitational system, offering significant insights into the formation pathways of binary black holes.”

This is still a very new science, with the ability to detect the gravitational waves of these black holes only going back as far as 2015. Since then, however, researchers have been able to identify about 300 separate merger events. With this being just the first that seems to be a part of a three-way merger, it is very likely that this type of thing is quite rare.

Stellar-mass black holes come in many sizes, but they do have an upper limit in terms of how massive they can be at the point of their formation. This is because when a massive star goes supernova, it sheds off its outer layers. From there, the core collapses to become a black hole. When stars above a certain size go supernova, however, they break apart entirely, scattering all the material out so that it cannot compress into a black hole.

So, the astronomers conclude, if they observe a black hole that has more mass than the upper limit of two stars, they can deduce that it must have come from three (or potentially more) combining.

The first black hole that was observed in this study published in the Astrophysical Journal Letters, GW190814, is not so massive. Instead, it is actually one of the smallest of its kind ever detected at just 2.6 times more massive than our own sun. The next black hole is quite a bit larger at 23 times larger than our sun.

It was this large contradiction in size that stood out since binary systems typically have similarly sized stars.

When the team, led by Shu-Cheng Yang of the Chinese Academy of Sciences saw this, they said that it likely indicates that the pair of black holes was brought together by a third gravitational object that is even bigger. When they looked at the gravitational wave data, they saw the pair of black holes orbiting around another point, which is where they believe the very large black hole may be.

Additional analysis is needed to confirm that this suspected third black hole is even there. When the LIGO-VIRGO-KAGRA gravitational wave observatories collect data for this part of the universe again, researchers will hopefully be able to get a clearer picture of what is really going on.

If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.