Abstract
Solitonic boson stars are stable objects made of a complex scalar field with a compactness that can reach values comparable to that of neutron stars. A recent study of the collision of identical boson stars produced only non-rotating boson stars or black holes, suggesting that rotating boson stars may not form from binary mergers. Here we extend this study to include an analysis of the gravitational waves radiated during the coalescence of such a binary, which is crucial to distinguish these events from other binaries with LIGO and Virgo observations. Our studies reveal that the remnant's gravitational wave signature is mainly governed by its fundamental frequency as it settles down to a non-rotating boson star, emitting significant gravitational radiation during this post-merger state. We calculate how the waveforms and their post-merger frequencies depend on the compactness of the initial boson stars and estimate analytically the amount of energy radiated after the merger.
Highlights
The direct detection of gravitational waves (GWs) by LIGO has begun a new era for strong-field gravity
Four events so far [1,2,3,4] appear to represent the inspiral, merger, and ring-down of binaries composed of two black holes (BHs), and an additional one is consistent with a binary neutron star system [5]
While BHs and neutron stars represent the standard model of compact objects, exploring the extent to which alternatives differ in their GW signatures remains an important test
Summary
The direct detection of gravitational waves (GWs) by LIGO has begun a new era for strong-field gravity. Motivated by the existent and future observations of compact object mergers, we study here the inspiral and merger of two BSs initially in a tight, quasicircular orbit The remnant of this merger can generally be either a BS or a BH. The merger of a pair of orbiting BSs produces a rotating remnant, the final object eventually settles down into a stationary nonrotating BS by radiating all its angular momentum via GW radiation and scalar field dispersion. Notice that similar scenarios were studied previously [21,22] in the context of mini BSs, which are much less compact than solitonic ones In those cases, the long dynamical time scales of the stars prevented definite conclusions about the end state of the remnants. BSs are self-gravitating compact objects made of a complex scalar field satisfying the Einstein-KleinGordon equations We present these equations, describe the initial data, detail the evolution formalism, and summarize the numerical techniques used to evolve a BS binary
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