Open AccessNewtonian hydrodynamics of the coalescence of black holes with neutron stars – II. Tidally locked binaries with a soft equation of state
Author(s) -
Lee William H.,
Kluźniak Włodzimierz
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02734.x
Subject(s) - physics , neutron star , schwarzschild radius , astrophysics , polytrope , black hole (networking) , stellar black hole , gravitational wave , equation of state , x ray burster , galaxy , polytropic process , stars , accretion (finance) , stellar evolution , stellar mass loss , quantum mechanics , computer network , routing protocol , routing (electronic design automation) , computer science , link state routing protocol
We present a numerical study of the hydrodynamics in the final stages of inspiral of a black hole–neutron star binary, when the binary separation becomes comparable to the stellar radius. We use a Newtonian three‐dimensional smooth particle hydrodynamics (SPH) code, and model the neutron star with a soft (adiabatic index Γ=5/3) polytropic equation of state, and the black hole as a Newtonian point mass that accretes matter via an absorbing boundary at the Schwarzschild radius. Our initial conditions correspond to tidally locked binaries in equilibrium, and we have explored configurations with different values of the mass ratio q M NS M BH , ranging from q =1 to 0.1. The dynamical evolution is followed for approximately 23 ms, and in every case studied here we find that the neutron star is tidally disrupted on a dynamical time‐scale, forming a dense torus around the black hole that contains a few tenths of a solar mass. A nearly baryon‐free axis is present in the system throughout the coalescence, and only modest beaming of a fireball that could give rise to a gamma‐ray burst would be sufficient to avoid excessive baryon contamination. We find that some mass (of the order of 10 −3 –10 −2 M ⊙ ) may be dynamically ejected from the system, and could thus contribute substantially to the amount of observed r‐process material in the galaxy. We calculate the gravitational radiation waveforms and luminosity emitted during the coalescence in the quadrupole approximation.