Spinning boson stars with large self-interaction

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Abstract
A rapidly spinning boson star of many solar masses, consisting of a gravitationally bound, massive scalar field with a large self-interaction parameter, may be detectable by gravitational-wave detectors if a particle (a neutron star or a small black hole) were to spiral into the boson star. Necessary for such detection is a knowledge of the boson star’s structure. This paper derives the equations governing that structure assuming the star to be stationary and axisymmetric. It is shown that the macroscopic structure of such a star is completely determined by only three parameters, which are related (probably by a one-to-one mapping for spinning stars) to its mass, spin, and quadrupole moment. The structure equations are solved numerically, and the resulting structure and stellar multipole moments are plotted in figures. From these figures and from gravitational-wave measurements of a candidate boson star’s mass, spin, quadrupole moment, and spin octopole moment, one can in principle confirm the existence of a boson star and determine all three of its parameters. Also discussed is the possibility of the particle inspiraling in the interior of the boson star.