After some historical remarks we discuss different criteria of dynamical stability of stars, and properties of the critical states where dynamical stability is lost, leading to collapse with formation of the neutron star or a black hole. At the end some observational and theoretical problems related to quark stars are discussed. 1. Introduction It was first noted by S Chandrasekhar in 1931 that...

We present two-dimensional simulations for the cooling of neutron stars with strong magnetic fields (B ≥ 1013 G). We study how the cooling curves are influenced by magnetic field decay. We show that the Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field and predict the surface temperature...

The existence of ultra-fast rotating neutron stars (spin period P ∼< 1 ms) is expected on the basis of current models for the secular evolution of interacting binaries, though they have not been detected yet. Their formation depends on the quantity of matter accreted by the neutron star which, in turn, is limited by the mechanism of mass ejection from the binary. An efficient mass ejection can ...

The energetics, spectrum, and composition of cosmic rays with energies below ∼ 10 eV are fairly well explained by models involving supernova shocks. In contrast, no widely accepted theory exists for the origin of ultra-high energy cosmic rays (UHECRS), which have energies above 10 eV. Instead of proposing a specific model, here we place strong constraints on any model of UHECRS involving isolat...

Context. The possibility of observationally discriminating between various types of neutron stars, described by different equations of state of the nuclear matter, as well as differentiating neutron stars from other types of exotic objects, like, for example, quark stars, is one of the fundamental problems in contemporary astrophysics. Aims. We consider and investigate carefully the possibility...

We present the second in a series of results in which we have searched for undiscovered neutron stars in supernova remnants (SNRs). This paper deals with the largest six SNRs in our sample, too large for Chandra or XMM-Newton to cover in a single pointing. These SNRs are nearby, with typical distances of < 1 kpc. We therefore used the ROSAT Bright Source Catalog and past observations in the lit...