I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to pro...

We investigate the relevance of the gravitational-wave driven r-mode instability for strange stars. We find that the unstable r-modes affect strange stars in a way that is quite distinct from the neutron star case. For accreting strange stars we show that the onset of r-mode instability does not lead to the thermo-gravitational runaway that is likely to occur in neutron stars. Instead, the stra...

We argue that if core collapse leads to the formation of a rapidly rotating proto-neutron star core or a fizzler surrounded by fall-back material, a lighter proto-neutron star forms around the main star moving in a super-close orbit, as an end result of a fully developed dynamical non-axisymmetric instability. Tidal mass exchange (even through a common envelope phase) propels the lighter star t...

In a cool neutron star (T . 10 K) endowed with a rather high magnetic field (B & 10 G), a phase transition may occur in the outermost layers. As a consequence the neutron star becomes “bare”, i.e. no gaseous atmosphere sits on the top of the crust. The surface of a cooling, bare neutron star does not necessarily emit a blackbody spectrum because the emissivity is strongly suppressed at energies...

We develop the general theory of stars in Saa’s model of gravity with propagating torsion and study the basic stationary state of neutron star. Our numerical results show that the torsion force decreases the role of the gravity in the star configuration and increases the maximum of the neutron star mass up to 5− 6M⊙ depending on the equation of state of matter. gr-qc/9803084

Helium star–compact object binaries, and helium star–neutron star binaries in particular, are widely believed to be the progenitors of the observed double neutron star systems. In these, the second neutron star is presumed to be the compact remnant of the helium star supernova. Here, the observational implications of such a supernova are discussed, and in particular are explored as a candidate ...

Aql X-1 is a soft X-ray transient source and emits type I X-ray bursts. A spectral state transition was observed with RXTE during its outburst decay in February and March 1997. Its 10-30 keV and 5-10 keV count rate ratio increased suddenly when its luminosity was between (4-12) E35 ergs/s, assuming a 2.5 kpc distance. Spectral fitting with a model composed of a blackbody and a power-law compone...

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extr...