Gravitational waves from dark boson star binary mergers

Abstract

Gravitational wave astronomy might allow us to detect the coalescence of low-brightness astrophysical compact objects which are extremely difficult to be observed with current electromagnetic telescopes. Besides classical sources like black holes and neutron stars, other candidates include Exotic Compact Objects (ECOs), which could exist in theory but have never yet been observed in Nature. Among different possibilities, here we consider Dark Stars, astrophysical compact objects made of dark matter such that only interact with other stars through gravity. We study numerically the dynamics and the gravitational waves produced during the binary coalescence of Dark Stars composed by bosonic fields. These results are compared both with Post-Newtonian approximations and with previous simulations of binary boson stars, which interact both through gravity and matter. Our analysis indicates that Dark Boson Stars belong to a new kind of compact objects, representing stars made with different species, whose merger produces a gravitational signature clearly distinguishable from other astrophysical objects like black holes, neutron stars and even boson stars.

Testing the nature of dark compact objects: a status report

“…If DM is built out of dark fermions, then formation should parallel that of standard neutron stars, and is also a well understood process. Collisions and merger of compact boson stars [54,415], boson-fermion stars [417,427], and axion stars [420,428] have been studied in detail.…”

“…Unfortunately, predictions for the coalescence in theories other than GR and for objects other that BHs are practically unknown. The exceptions concern evolutions of neutron stars, boson stars, composite fluid systems, and axion stars [54,135,415,417,420,425,427,428] (see Sec. 4.6), and recent progress in BH mergers in modified gravity [522][523][524][525].…”

Gravitational wave signatures of dark matter cores in binary neutron star mergers by using numerical simulations

“…Note that the merger of DM cores with no fermionic matter, so-called boson stars, have been previously studied both in the NISF [39] and in the ISF cases [34,40]. Here we focus on FBSs only.…”

“…Our numerical implementation has been tested with several benchmark problems dealing with Einstein-KG equations [34,39,40,57,58] and GRHD equations [59][60][61].…”

Exploring strong-field deviations from general relativity via gravitational waves

“…Various specific models for departure from BH predictions for GW signatures have also been considered, including boson and fermion stars (see e.g. [32][33][34]) and Proca stars [35]. However, the resulting solutions have characteristic sizes determined by mass parameters of the underlying theory, so do not provide models for quantum behavior of BHs of arbitrary size, and also do not typically achieve the highest range of compactness.…”