Do black holes remember what they are made of?

Understand

We study the ringdown signal of black holes formed in prompt-collapse binary neutron star mergers.

• We analyze data from $47$ numerical relativity simulations.
• We show that the $(\ell=2,m=2)$ and $(\ell=2,m=1)$ multipoles of the gravitational wave signal are well fitted by decaying damped exponentials, as predicted by black-hole perturbation theory.
• We show that the ratio of the amplitude in the two modes depends on the progenitor binary mass ratio $q$ and reduced tidal parameter $\tilde\Lambda$.