Ke-Jian Jin | Searcharxiv

arXiv2007

Critical Phenomena in Head-on Collisions of Neutron Stars

We found type I critical collapses of compact objects modeled by a polytropic equation of state (EOS) with polytropic index $Γ=2$ without the ultra-relativistic assumption. The object is formed in head-on collisions of neutron stars. Further we showed that the critical collapse can occur due to a change of the EOS, without fine tuning of initial data. This opens the possibility that a neutron star like compact object, not just those formed in a collision, may undergo a critical collapse in processes which slowly change the EOS, such as cooling.

gr-qc↗

arXiv1999

Gravitational Lensing Effects of Fermion-Fermion Stars: I. Strong Field Case

We investigate a two-component model for gravitational lenses, i.e., the fermion-fermion star as a dark matter self-gravitating system made from two kinds of fermions with different masses. We calculate the deflection angles varying from arcseconds to even degrees. There is one Einstein ring. In particular, we find three radial critical curves for radial magnifications and four or five images of a point source. These are different from the case of the one-component model such as the fermion stars and boson stars. This is due to the fermion-fermion star being a two-component concentric sphere. Our results suggest that any possible observations of the number of images more than 3 could imply a polytropic distribution of the mass inside the lens in the universe.

gr-qc↗