  Black holes in scalar-Gauss-Bonnet gravity are prone to scalarization, that
is a spontaneous development of scalar hair for strong enough spacetime
curvature while the weak field regime of the theory coincides with general
relativity. Since large spacetime curvature is associated with smaller black
hole masses, the merging of black holes can lead to dynamical descalarization.
This is a spontaneous release of the scalar hair of the newly formed black hole
in case its mass is above the scalarization threshold. Depending on the exact
form of the Gauss-Bonnet coupling function, the stable scalarized solutions can
be either continuously connected to the Schwarzschild black hole, or the
transitions between the two can happen with a jump. By performing simulations
of black hole head-on collisions in scalar-Gauss-Bonnet gravity prone to
dynamical descalization, we have demonstrated that such a jump can be clearly
observed in the accumulated gravitational wave data of multiple merger events
with different masses. The distinct signature in the gravitational wave signal
will share similarities with the effects expected from first order matter phase
transitions happening during neutron star binary mergers.
