Gravitational Waves from Binary Black Hole Mergers Inside of Stars

Understand

We present results from a controlled numerical experiment investigating the effect of stellar density gas on the coalescence of binary black holes (BBHs) and the resulting gravitational waves (GWs).

• This investigation is motivated by the proposed stellar core fragmentation scenario for BBH formation and the associated possibility of an electromagnetic counterpart to a BBH GW event.
• We employ full numerical relativity coupled with general-relativistic hydrodynamics and set up a $30 + 30 M_\odot$ BBH (motivated by GW150914) inside gas with realistic stellar densities.
• Our results show that at densities $\rho \gtrsim 10^6 - 10^7 \, \mathrm{g \, cm}^{-3}$ dynamical friction between the BHs and gas changes the coalescence dynamics and the GW signal in an unmistakable way.