Boson star-black hole binaries: initial data and head-on collisions

Abstract

We present a numerical-relativity study of comparable-mass boson star-black hole (BS-BH) head-on collisions, focusing on both initial-data construction and gravitational-wave (GW) phenomenology. We show that plain superposition can strongly perturb the BS core, leading to large constraint violations and unphysical radial oscillations. To remedy this problem, we introduce a one-body conformal-factor correction and find that it substantially suppresses these artifacts. Using the improved initial data, we analyze GW emission from equal- and unequal-mass BS-BH binaries and compare with matched BS-BS and BH-BH baselines. For equal masses, the BS-BH radiated energy increases with BS compactness and approaches the BH-BH limit for highly compact stars. For unequal masses, the $q=2$ BS-BH configuration in our sample radiates slightly more GW energy than its matched BH-BH counterpart.

25 pages, 16 figures; v3: the (3,0) mode recast as a numerical cautionary example; to appear in Physical Review D; data publicly available at https://github.com/zhuan-ning/boson-star-black-hole-head-on-data