On 14 July 2025, the LIGO-Virgo-KAGRA Collaboration announced the discovery of GW231123, the merger of the most massive black holes ever observed with gravitational waves, using the US National Science Foundation-funded (NSF) LIGO Hanford and Livingston Observatories. The two black holes that merged were approximately 100 and 140 times the mass of the Sun. The merger produced a final black hole more than 225 times the mass of our Sun. The signal was observed during the fourth observing run (O4) of the LVK network on November 23, 2023. 

Link to article: https://arxiv.org/abs/2507.08219

A team of international scientists has discovered the largest merger of two black holes ever. The discovery has been met with enthusiasm by fellow scientists around the world.

The merger was observed using gravitational waves. A black hole is characterized by an extremely strong gravitational field from which nothing can escape, not even light.

The merger of two black holes has now been observed about three hundred times, says Selma de Mink, director at the Max Planck Institute for Astrophysics. This discovery is remarkable because it involves the most massive black holes ever discovered.

"The black holes are so massive and orbit each other so rapidly that space-time was distorted, as predicted by Einstein's general theory of relativity," says De Mink. "These ripples eventually reached Earth and were measured with incredibly sensitive equipment." 225 times the mass of the sun

The merger of the black holes created a black hole more than 225 times the mass of our sun. The merger occurred approximately 10 billion light-years from Earth. One light-year is approximately 9.5 trillion kilometers.

According to scientists, the two black holes were also the result of previous mergers and were therefore already more massive than average.

Using gravitational wave detectors on Earth, scientists can detect signals from a merger. "Although this is one of the most violent events in the universe that we can observe, the signals we receive from it on Earth are so faint that we can barely detect them," says one of the researchers.

The measurements were taken on November 23, 2023, at two different detectors in the US. Researchers observed a tenth-of-a-second discrepancy in the measurements. This indicates the moment when both black holes violently merged before settling into a single black hole.

The latest results allow scientists to conduct further research into how black holes are formed and how they converge. This will allow scientists to learn more about the development and origins of the universe, among other things.