We present the first direct comparison of numerical simulations of neutron star-black hole and black hole-black hole mergers in full general relativity .
We focus on a configuration with non spinning objects and within the most likely range of mass ratio for neutron star-black hole systems ( q = 6 ) .
In this region of the parameter space , the neutron star is not tidally disrupted prior to merger , and we show that the two types of mergers appear remarkably similar .
The effect of the presence of a neutron star on the gravitational wave signal is not only undetectable by the next generation of gravitational wave detectors , but also too small to be measured in the numerical simulations : even the plunge , merger and ringdown signals appear in perfect agreement for both types of binaries .
The characteristics of the post-merger remnants are equally similar , with the masses of the final black holes agreeing within \delta M _ { BH } < 5 \times 10 ^ { -4 } M _ { BH } and their dimensionless spins within \delta \chi _ { BH } < 10 ^ { -3 } .
The rate of periastron advance in the mixed binary agrees with previously published binary black hole results , and we use the inspiral waveforms to place constraints on the accuracy of our numerical simulations independent of algorithmic choices made for each type of binary .
Overall , our results indicate that non-disrupting neutron star-black hole mergers are exceptionally well modeled by black hole-black hole mergers , and that given the absence of mass ejection , accretion disk formation , or differences in the gravitational wave signals , only electromagnetic precursors could prove the presence of a neutron star in low-spin systems of total mass \sim 10 M _ { \odot } , at least until the advent of gravitational wave detectors with a sensitivity comparable to that of the proposed Einstein Telescope .