Equal-mass binaries correspond to a discontinuous limit in the spin precession equations. A new constant of motion pops up, which can be exploited to study the dynamics. This is a really neat calculation done with Jakub, a Cambridge undergraduate student. Also, my first paper at Caltech!
Here we present 1+1 numerical-relativity simulation of stellar collapse in scalar-tensor theories, where gravity is mediated by the usual metric coupled to an additional scalar field. Bottom line: you can test General Relativity with supernovae explosions!
Supporting material available here.
What happens if you throw a scalar field into General Relativity? And if you throw more than one? Here is a paper on the phenomenology of neutron stars in theories with more than one scalar field coupled to gravity.