We compute zero-frequency (neutral) quasi-normal f -modes of fully relativistic and rapidly rotating neutron stars, using several realistic equations of state (EOSs) for neutron star matter. The zero-frequency modes signal the onset of the gravitational radiation-driven instability. We find that the l = m = 2 (bar) f -mode is unstable for stars with gravitational mass as low as 1.0 − 1.2M⊙, dep...

We reanalyze the r-mode instability in rotating superfluid neutron stars. To this aim we develop a model of resonance interaction of normal m = 2 r-mode with superfluid modes. We show that this interaction dramatically modifies the instability window, that is the region of stellar spin frequencies and temperatures in which a neutron star becomes unstable with respect to radiation of gravitation...

The nature of the 5 − 12 s “anomalous” X-ray pulsars (AXPs) remains a mystery. Among the models that have been proposed to explain the properties of AXPs, the most likely ones are: (1) isolated accreting neutron stars evolved from the Thorne-Żytkow objects (TŻOs ) due to complete spiral-in during the common envelope (CE) evolution of high-mass X-ray binaries (HMXBs), and (2) magnetars, which ar...

The isolated neutron star RX J185635-3754 is the closest known neutron star to the Sun. Based on HST WFPC2 obervations over a 3 year baseline, I report its proper motion (332±1 mas yr at a position angle of 100.3±0.1) and parallax (16.5±2.3 mas; 61 pc). This proper motion brings the neutron star from the general vicinity of the Sco-Cen OB association. For an assumed neutron star radial velocity...

The contribution of weakly–magnetized (B ∼ 10 G) neutron stars accreting the interstellar medium to the diffuse X–ray emission observed in the Galactic Center is investigated. It is shown that, under rather conservative assumptions about the neutron stars and gas distributions, the accretion luminosity can account for a sizable fraction, possibly most, of the detected X–ray flux in the 2.5–7 ke...

We report on numerical results from an independent formalism to describe the quasiequilibrium structure of nonsynchronous binary neutron stars in general relativity. This is an important independent test of controversial numerical hydrodynamic simulations which suggested that nonsynchronous neutron stars in a close binary can experience compression prior to the last stable circular orbit. We sh...

Ultramagnetized neutron stars or magnetars have been invoked to explain several astrophysical phenomena. We examine how the magnetic field of a magnetar will decay over time and how this decay affects the cooling of the object. We find that for sufficiently strong nascent fields, field decay alters the cooling evolution significantly relative to similarly magnetized neutron stars with constant ...

Recent work has raised the exciting possibility that r-mode pulsations (Rossby waves) in rotating neutron star cores may be strong gravitational wave sources. Rapidly rotating young neutron stars born in supernovae enter the r-mode instability region within the first minutes of their lives and may spin down by substantial amounts due to gravitational radiation from r-modes. Accreting neutron st...

ASTRONOMY AND ASTROPHYSICS The birth of strange stars and their dynamo-originated magnetic fields Abstract. It is shown that protostrange stars (PSSs) can be convective and that there are two possible scenarios describing their turbulence. Besides the local turbulence on the scale which is less than the mean free path of neu-trinos, large-scale (∼ 1 km) convection also may occur with properties...

Recent ROSAT measurements show that the x-ray emission from isolated neutron stars is modulated at the stellar rotation period. To interpret these measurements, one needs precise calculations of the heat transfer through the thin insulating envelopes of neutron stars. We present nearly analytic models of the thermal structure of the envelopes of ultramagnetized neutron stars. Specifically, we e...