'Invisible Giant' Discovered Hiding Behind Double Black Holes

DNVN - Gravitational waves from the GW190814 event have revealed traces of the existence of a hidden supermassive black hole nearby, opening up a new perspective on how binary black holes form.

Binary black hole merger near a supermassive black hole. Source: SHAO

Binary black holes are already one of the most mysterious phenomena in the universe, but scientists at the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences have recently found evidence that they may not be alone. Some binary black hole systems are likely dominated by a mysterious “giant companion” nearby.

A research team led by Dr Wenbiao Han at SHAO reported signs that the binary black hole merger event GW190814 likely occurred under the gravitational influence of a third object - possibly a supermassive black hole itself.

The research results, published in the Astrophysical Journal Letters, provide important clues to deciphering the origin of binary black holes.

Gravitational wave event detected by the LIGO-Virgo-KAGRA collaboration. Source: SHAO

Since 2015, the LIGO-Virgo-KAGRA collaboration has detected more than 100 gravitational wave events, mainly originating from binary black hole mergers. Although they have contributed to a better understanding of the physics of the universe, the mechanism by which they form and evolve is still not fully understood.

Previously, Dr. Han’s team proposed the “b-EMRI” model, which describes a scenario where a supermassive black hole “captures” a binary black hole, forming a three-tiered system. In this structure, the binary black hole pair orbits the supermassive black hole and emits gravitational waves at multiple frequency bands. The model was included in a LISA white paper and identified as an important research target for China’s space gravitational wave observatories. Since then, scientists have been searching for signs of binary black hole mergers near the supermassive black hole in LIGO-Virgo data.

When analyzing the GW190814 data, the researchers found that the two merging black holes had a mass ratio of nearly 10:1. According to co-author Dr Shucheng Yang, this imbalance likely suggests that the pair were once part of a triple system, with the supermassive black hole pulling them together through gravitational interactions. Another hypothesis is that they formed within the accretion disk of an active galactic nucleus, where the gravity of dense objects drove the merger.

Scientists believe that if the binary black holes merge near a third solid object, the orbit around this object will create a line-of-sight acceleration – that is, acceleration along the observer’s line of sight. This acceleration changes the frequency of the gravitational waves through the Doppler effect, leaving a “fingerprint” in the signal.

Parameter estimates for GW190814, including the masses of the two black holes (*m*~1~ and *m*~2~), the luminosity separation (*d*~L~), the line-of-sight acceleration (*a*), and the power index (*n*~I~). Dashed lines indicate the median values ​​and 90% confidence intervals. Contour plots show the 50% and 90% confidence intervals. Source: SHAO

To determine this, the team developed a gravitational wave model that incorporates line-of-sight acceleration and applied Bayesian analysis to several events with strong signals. The results showed that for GW190814, the line-of-sight acceleration model outperformed the isolated binary black hole hypothesis.

This acceleration is estimated to be about 0.002 c/s-1 (90% confidence level, where c is the speed of light), giving a Bayes factor of 58:1 - strong evidence for the existence of line-of-sight acceleration.

“This is the first international evidence for the presence of a third compact object in a binary black hole merger,” Dr Han said. “This finding suggests that the binary black hole in GW190814 may be part of a complex system, rather than forming independently, opening up new perspectives on the mechanism of binary black hole formation.”

In the future, when new generations of gravitational wave detectors such as the Einstein Telescope, Cosmic Explorer or space devices LISA, Taiji, TianQin come into operation, scientists expect to be able to detect small changes in signals with high precision. That will help people decode more events like GW190814, getting closer to explaining the formation and evolution of binary black holes.

La Khe (According to SciTech Daily)

Source: https://doanhnghiepvn.vn/cong-nghe/phat-hien-nguoi-khong-lo-vo-hinh-an-minh-sau-ho-den-doi/20250901102834250