Abstract
Neutron stars (NSs) powered by accretion, which are known as accretion-powered NSs, always are located in binary systems and manifest themselves as X-ray sources. Physical processes taking place during the accretion of material from their companions form a challenging and appealing topic, because of the strong magnetic field of NSs. In this paper, we review the physical process of accretion onto magnetized NS in X-ray binary systems. We, firstly, give an introduction to accretion-powered NSs and review the accretion mechanism in X-ray binaries. This review is mostly focused on accretion-induced evolution of NSs, which includes scenario of NSs both in high-mass binaries and in low-mass systems.
Highlights
Introduction to AccretionPowered Neutron StarSince the discovery for the first extrasolar X-ray source, Scorpius X-1 in 1962 [1], a new field of astronomy—accreting compact objects in the galaxy—has arisen, which offers unique insight into the physics at extreme conditions
It was suggested that the strong galactic X-ray sources are Neutron stars (NSs) accreting material from their companions in close binary systems [2]
The currents confine the magnetic field inside a screening radius rs ∼ (10–100)rcor, which gives the extent of transition zone
Summary
Since the discovery for the first extrasolar X-ray source, Scorpius X-1 in 1962 [1], a new field of astronomy—accreting compact objects in the galaxy—has arisen, which offers unique insight into the physics at extreme conditions. The companions in HMXBs are bright and luminous early-type Be or OB supergiant stars, which have masses larger than 10 solar masses and are short lived and belong to the youngest stellar population in the galaxy, with ages of ∼105–107 yrs [14,15,16] They are distributed close to the galactic plane. X-ray binaries, with companion mass, ≤ M⊙, are categorized as low-mass X-ray binaries (LMXBs), in which mass transfer takes place by Roche-lone overflow This transfer is driven either by losing angular momentum due to gravitational radiation (for systems of very small masses and orbital separations) and magnetic braking (for systems of orbital periods Porb ≤ 2 days) or by the evolution of the companion star (for systems of Porb ≥ 2 days). Intermediate-mass systems are rare, since mass transfer via Roche lobe is unstable and would lead to a very quick (∼103–105 yrs) evolution of the system, while, in the case of stellar wind accretion, the mass accretion rate is very low and the system would be very dim and hardly detectable [23]
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