I "Testing the black-hole area law with GW150914"

[robphy]

(I haven't been actively following this line of research... but I think it is possibly interesting reading.
It's been in the science news today.)

"Black Hole Area Law Tested" (synopsis)
https://physics.aps.org/articles/v14/s87

"Testing the Black-Hole Area Law with GW150914"
Maximiliano Isi, Will M. Farr, Matthew Giesler, Mark A. Scheel, and Saul A. Teukolsky
Phys. Rev. Lett. 127, 011103 – Published 1 July 2021
http://dx.doi.org/10.1103/PhysRevLett.127.011103 (preprint: https://arxiv.org/abs/2012.04486 )

We present observational confirmation of Hawking’s black-hole area theorem based on data from GW150914, finding agreement with the prediction with 97% (95%) probability when we model the ringdown including (excluding) overtones of the quadrupolar mode. We obtain this result from a new time-domain analysis of the pre- and postmerger data. We also confirm that the inspiral and ringdown portions of the signal are consistent with the same remnant mass and spin, in agreement with general relativity.