The multifaceted role of the density dependent nuclear symmetry energy in the nuclear astrophysics involving neutron stars is highlighted. Efforts toward a model independent determination of the dense matter equation state through a deconstruction of the neutron star structure equation utilizing the masses and radii of several individual neutron stars are described. The need for observational d...

We have calculated the evolution of 60 model binary systems consisting of helium stars in the mass range of MHe = 2.5 − 6M⊙ with a 1.4 M⊙ neutron star companion to investigate the formation of double neutron star systems. Orbital periods ranging from 0.09 to 2 days are considered, corresponding to Roche lobe overflow starting from the helium main sequence to after the ignition of carbon burning...

After 3 years of quiescence, the globular cluster NGC 6440 exhibited a bright transient X-ray source turning on in August 2001, as noted with the RXTE AllSky Monitor. We carried out a short target of opportunity observation with the Chandra X-ray Observatory and are able to associate the transient with the brightest of 24 X-ray sources detected during quiescence in July 2000 with Chandra. Furth...

I discuss three-dimensional SPH simulations of neutron star black hole (BH) encounters. The calculations are performed using a nuclear equation of state and a multi-flavor neutrino treatment, general relativistic effects are mimicked using the Paczynski-Wiita pseudo-potential and gravitational radiation reaction forces. Most of the explored mass range (14 to 20 M⊙) has not been considered befor...

We study the effect of the kick velocity – neutron star spin alignment observed in young radio pulsars on the coalescence rate of binary neutron stars. The effect is shown to be especially strong for large kick amplitudes and tight alignments, reducing the galactic rate of binary neutron star coalescences up to an order of magnitude with respect to the rates calculated for random kicks. The spi...

The possibility of the existence of quark matter dates back to early seventies. Bodmer remarked that matter consisting of deconfined up, down and strange quarks could be the absolute ground state of matter at zero pressure and temperature. If this is true then objects made of such matter, so-called ”strange star”, could exist. There are several proposed mechanisms for formation of quark stars. ...

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 other possibilities. In particular neutron star + massive white dwarf has several desirable features. These systems are likely to pr...

Anomalous X-ray pulsars, compact non-pulsing X-ray sources in supernova remnants, and X-ray bursters are three distinct types of sources for which there are viable models that attribute their Xray emission to thermal emission from the surface of a neutron star. Inferring the surface area of the emitting regions in such systems is crucial in assessing the viability of different models and in pro...