Spherical Einstein-Friedberg-Lee-Sirlin boson stars: Self-interacting solutions and their astrophysical appearance

Abstract: We investigate boson stars within the framework of the self-interacting Einstein-Friedberg-Lee-Sirlin (E-FLS) model, constituted by a complex scalar field with a quartic self-interaction and a real scalar field. Our analysis explores the family of static solutions across a broad range of parameters, including the self-interaction of the complex scalar field. We obtain that positive self-interaction terms increase the maximum mass and compactness of E-FLS stars, allowing them to reach masses comparable to the Chandrasekhar limit without the need of ultralight bosonic masses. Moreover, in the limit where the real scalar field becomes massless, the solutions present larger effective radii and allow a broader range of stable solutions. Astrophysical images, generated via backward ray-tracing, show that these compact, self-interacting E-FLS stars produce strong gravitational lensing, yielding shadows that could visually mimic black holes, thus providing potential observational signatures detectable in ongoing electromagnetic surveys.