Gravitational decoupling of generalized Horndeski hybrid stars

Exploring gravitational theories beyond Horndeski

We have recently proposed a new class of gravitational scalar-tensor theories free from Ostrogradski instabilities, in Ref. [1]. As they generalize Horndeski theories, or “generalized” galileons, we call them G. These theories possess a simple formulation when the time hypersurfaces are chosen to coincide with the uniform scalar field hypersurfaces. We confirm that they contain only three propa...

Gravitational vacuum condensate stars.

A new final state of gravitational collapse is proposed. By extending the concept of Bose-Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate p(v) = -rho(v) and an exterior Schwarzschild geometry of arbitrary total mass M is constructed. These regions are separated by a shell with a small but finite proper thickness l of fluid with ...

Gravitational lensing by rotating stars

The equations giving the position of the images of a point source by a rotating point lens are derived by a new, elementary method. It is shown that only two of the three images are visible. It is argued that the projection of the angular momentum of the lens star on the lens plane can be measured if the lens is a rapidly rotating early type star. This is achieved by performing a series of astr...

Gravitational waves from neutron stars

Gravitational Waves from Relativistic Stars

The amplitude of gravitational waves is quite tiny, although they carry enormous amount of energy. They propagate without suffering any disturbance after leaving the sources. The observation gives the direct information of the emission regions. The gravitational wave astronomy in the next century will therefore be an invaluable tool to diagnose the interior structure of the relativistic stars. ...