Structure of neutron stars in massive scalar-tensor gravity

Understand

We compute families of spherically symmetric neutron-star models in two-derivative scalar-tensor theories of gravity with a massive scalar field.

• The numerical approach we present allows us to compute the resulting spacetimes out to infinite radius using a relaxation algorithm on a compactified grid.
• We discuss the structure of the weakly and strongly scalarized branches of neutron-star models thus obtained and their dependence on the linear and quadratic coupling parameters $\alpha_0$, $\beta_0$ between the scalar and tensor sectors of the theory, as well as the scalar mass $\mu$.
• For highly negative values of $\beta_0$, we encounter configurations resembling a "gravitational atom", consisting of a highly compact baryon star surrounded by a scalar cloud.