Recent gravitational wave observation based on the data from GW150914 has confirmed Hawking’s area theorem and estimated the increase in total horizon area during a merger process of two Kerr black holes. We use this result and the validity of the second law to obtain the first observational bound on the 4D topological Gauss-Bonnet coupling as $\gamma \lesssim 2.804_{-1.169}^{+7.946}\times {10}^9{\mathrm{m}}^2$ with 95% credibility.

• Received 21 January 2022
• Accepted 3 August 2022

DOI:https://doi.org/10.1103/PhysRevD.106.L041503