Gravitational waves were first detected ten years ago, and just recently, scientists captured the clearest gravitational wave signal yet, confirming Stephen Hawking's famous prediction. With the help of upgraded LIGO and other detectors, researchers observed the collision of two black holes more than a billion light-years away. The ripples in space-time produced by this cosmic violent event were so precise that scientists described themselves as "hearing" the black hole vibrating like a cosmic bell.
On September 14, 2015, scientists confirmed for the first time the weak gravitational wave signal from the merger of two black holes 130 million light-years away. The signal traveled through the universe for 1.3 billion years before reaching the earth. Gravitational waves were a theoretical prediction put forward by Einstein a hundred years ago, but it was not until that day that humans recorded real gravitational waves using LIGO's dual detectors. It was announced in 2016 that it won the 2017 Nobel Prize in Physics.
Today, the LIGO observatories in Hanford and Louisiana in the United States join forces with the Italian Virgo detector and Japan's KAGRA to form the global gravitational wave detection network LVK. So far, the network has discovered more than 300 black hole and neutron star merger events, and there are as many as 230 candidate events for the 2025 observation period alone, which is an impressive achievement. These advances are all due to more advanced quantum precision instruments, allowing LIGO and Virgo to detect spatial disturbances 700 trillion times thinner than a hair.
The clearest signal this time comes from the black hole merger event GW250114 on January 14, 2025. It is similar to the first GW150914 event. Both black holes have a mass of 30 to 40 times that of the sun and are about 1.3 billion light-years away from the earth. However, after ten years of technological progress, the GW250114 signal appears particularly clearly after the instrument noise is greatly reduced.
This signal provides the best observational evidence to date for testing the "black hole area theorem" proposed by Hawking in 1971. This theorem states that the total surface area of a black hole never decreases. After two black holes merge, the surface area should increase, albeit slightly due to the loss of energy in the form of gravitational waves, but the total area must grow. This study found that the initial black hole total area was about 240,000 square kilometers, which increased to about 400,000 square kilometers after the merger, clearly confirming Hawking's theory.
When the merger process enters what's known as the "reverberation" phase, the new black hole vibrates like a bell being struck. For the first time, researchers have clearly measured this stage. By analyzing different frequency patterns of gravitational waves, they can accurately calculate the final black hole mass and spin, and thus calculate the area change. Further analysis also provided an extremely rigorous test of the general relativity model.
The LVK network has also discovered numerous cosmic merger events in the past ten years, including neutron star collisions (such as the famous gold eruption event in 2017), the first black hole-neutron star collision, asymmetric mass mergers, and the most massive black hole collision ever discovered, etc., constantly refreshing the boundaries of human understanding of the universe.
In the future, scientists hope to use the new generation of European "Einstein Telescope" and the American "Cosmic Explorer" and other larger-scale detectors to push mankind's "echoes" on the merger of black holes in the early universe and even the origin of the universe further into the depths of space and time.
"Today is the golden age of gravitational wave research, and global cooperation has allowed us to explore the mysteries of the dark universe." Professor Massimo Carpinelli, head of the European Gravitational Observatory, said, "New larger detectors are already in preparation, and we are confident to meet the challenges of the future."
Compiled from /ScitechDaily