A long journey to gravitational waves: the evolution of supermassive black home binaries in galaxy merger remnants

Massive black hole binaries are among the most promising gravitational wave sources 
detectable by the forthcoming LISA observatory. Massive black hole pairs are expected 
to form in the aftermath of galaxy mergers, and their coupling in dry merger relics 
can be described as a three-step process: (i) a dynamical friction dominated phase, 
(ii) a migration phase induced by slingshot ejections of stars, and (iii) a 
gravitational-wave driven inspiral leading to rapid coalescence. However, the 
slingshot-driven pairing may be ineffective if too few stars are scattered in the 
vicinity of the black hole binary, and the shrinking may come to a halt at roughly 
parsec separation: this is the famous 'final parsec problem'. In this seminar, I 
will review the final parsec problem and its proposed solutions; I will elaborate 
on the recent developments in the study of the dynamics of massive binaries; finally, 
I will discuss the importance of galaxy properties in ensuring a rapid binary 
coalescence in gas-poor systems.