Speaker
Alessandro Drago
(FE)
Description
The existence of neutron stars with masses of 2 solar masses requires a stiff
equation of state at high densities. On the other hand, the necessary
appearance also at high densities of new degrees of freedom, such as
hyperons and ? resonances, can lead to a strong softening of the equation
of state with resulting maximum masses of 1.5 solar masses and radii smaller than 10 km. Hints for the existence of compact stellar objects with very small
radii have been found in recent statistical analysis of quiescent low-mass
X-ray binaries in globular clusters. We propose an interpretation of these
two apparently contradicting measurements, large masses and small radii,
in terms of two separate families of compact stars: hadronic stars, whose
equation of state is soft, can be very compact, while quark stars, whose
equation of state is stiff, can be very massive. In this respect an early
appearance of ? resonances is crucial to guarantee the stability of the
branch of hadronic stars. Our proposal could be tested by measurements of
radii with an error of 1 km, which is within reach of the planned LOFT
satellite, and it would be further strengthened by the discovery of
compact stars heavier than 2 solar masses.
Reference: A.D., A.Lavagno and G.Pagliara Phys.Rev. D89 (2014) 043014
