Stars or gas? Constraining the hardening processes of massive black-hole binaries with LISA

To Stars or to gas, that is the question.
Whether ’tis nobler in the hardening to suffer
The slings and arrows of passing stars,
Or to dissipate against a sea of gas
And by disk end them. To inspiral — to merge,
No more; and by LISA to say we end
The models and the thousand PE samples
That gravity is heir to.

Alice Spadaro, Riccardo Buscicchio, David Izquierdo-Villalba, Davide Gerosa, Antoine Klein, Geraint Pratten.
arXiv:2409.13011 [astro-ph.HE].