10 years of gravitational waves: from the first detection to GW250114

On September 14, 2015, the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected a gravitational wave (GW150914) for the first time—the vibration of spacetime caused by the collision of two black holes. This historic moment confirmed Einstein’s century-old prediction and opened a new era for astrophysics.

In ten years, the international LIGO-Virgo-KAGRA detector network has observed more than three hundred gravitational-wave signals. Among these signals, one of the most remarkable is the merger of two black holes detected by LIGO on January 14, 2025. This gravitational-wave signal (called GW250114), the clearest ever observed thanks in particular to the improved sensitivity of the instruments, allows us to measure the properties of black holes with unprecedented precision and to rigorously test the fundamental predictions of general relativity.

As Thibault Damour, Permanent Professor at IHES, emphasizes:

“Black holes are one of the most remarkable predictions of Einstein’s theory of General Relativity. For a long time, these objects remained mere theoretical speculations. GW250114 provides the first precise confirmation that the gravitational-wave signal emitted during the merger of two black holes ends with exponentially damped oscillations, as predicted by Einstein’s theory, and as shown in the figure below.”

The article GW250114: testing Hawking’s area law and the Kerr nature of black holes, accepted for publication in Physical Review Letters and co-signed by Thibault Damour, Permanent Professor at IHES, contains two spectacular results:

• The final black hole “rings” exactly as predicted by general relativity for a rotating black hole (described by the exact solution found by Roy Kerr in 1963).

• Hawking’s black hole area theorem (1971) is verified: the area of the final black hole’s surface is larger than the sum of the areas of the two initial black holes.

One of the key elements enabling this breakthrough is the Effective-One-Body (EOB) method, developed at IHES, which makes it possible to model the dynamics of black hole mergers with great accuracy. Two variants of this method—TEOB (developed by A. Nagar, a regular visitor at IHES) and SEOB (developed by A. Buonanno)—were used to analyze the GW250114 signal.

In just ten years, we have moved from the first gravitational wave (GW150914) to profound experimental confirmations of Einstein’s theory of gravitation. The EOB method, conceived and developed at IHES, has played—and continues to play—a key role in this thrilling scientific adventure.

Caption and credit of the image at the top of the article:
LIGO operates two detectors located 3000 km (1800 miles) apart: One in eastern Washington near Hanford, and the other near Livingston, Louisiana. This photo shows the Livingston detector.
© Caltech/MIT/LIGO Lab