Disk luminosity and angular momentum for accreting, weak field neutron stars in the ‘Slow’ rotation approximation

1995 ◽  
Vol 16 (3-4) ◽  
pp. 357-374 ◽  
Author(s):  
Bhaskar Datta ◽  
Arun V. Thampan ◽  
Paul J. Wiita
Keyword(s):  
Angular Momentum ◽  
Neutron Stars ◽  
Weak Field ◽  
Slow Rotation

Propagation of internal gravity waves in fluids with shear flow and rotation

1967 ◽  
Vol 30 (3) ◽  
pp. 439-448 ◽  
Author(s):  
Walter L. Jones
Keyword(s):  
Angular Momentum ◽  
Shear Flow ◽  
Gravity Waves ◽  
Shear Flows ◽  
Internal Gravity Waves ◽  
Vertical Transport ◽  
Wave Frequency ◽  
Slow Rotation ◽  
Critical Levels ◽  
Rotating System

In a rotating system, the vertical transport of angular momentum by internal gravity waves is independent of height, except at critical levels where the Doppler-shifted wave frequency is equal to plus or minus the Coriolis frequency. If slow rotation is ignored in studying the propagation of internal gravity waves through shear flows, the resulting solutions are in error only at levels where the Doppler-shifted and Coriolis frequencies are comparable.

scholarly journals Radiation of Angular Momentum by Neutrinos from Merged Binary Neutron Stars

1998 ◽  
Vol 504 (1) ◽  
pp. 431-441 ◽  
Author(s):  
Thomas W. Baumgarte ◽  
Stuart L. Shapiro
Keyword(s):  
Angular Momentum ◽  
Neutron Stars ◽  
Binary Neutron Stars

scholarly journals Angular momentum transport in massive stars and natal neutron star rotation rates

2019 ◽  
Vol 488 (3) ◽  
pp. 4338-4355 ◽  
Author(s):  
Linhao Ma ◽  
Jim Fuller
Keyword(s):  
Angular Momentum ◽  
Massive Stars ◽  
Baroclinic Instability ◽  
Core Collapse ◽  
Slow Rotation ◽  
Low Mass Stars ◽  
Rotation Rates ◽  
Rotation Periods ◽  
Low Mass ◽  
Binary Evolution

Abstract The internal rotational dynamics of massive stars are poorly understood. If angular momentum (AM) transport between the core and the envelope is inefficient, the large core AM upon core-collapse will produce rapidly rotating neutron stars (NSs). However, observations of low-mass stars suggest an efficient AM transport mechanism is at work, which could drastically reduce NS spin rates. Here, we study the effects of the baroclinic instability and the magnetic Tayler instability in differentially rotating radiative zones. Although the baroclinic instability may occur, the Tayler instability is likely to be more effective for AM transport. We implement Tayler torques as prescribed by Fuller, Piro, and Jermyn into models of massive stars, finding they remove the vast majority of the core’s AM as it contracts between the main-sequence and helium-burning phases of evolution. If core AM is conserved during core-collapse, we predict natal NS rotation periods of $P_{\rm NS} \approx 50\!-\!200 \, {\rm ms}$, suggesting these torques help explain the relatively slow rotation rates of most young NSs, and the rarity of rapidly rotating engine-driven supernovae. Stochastic spin-up via waves just before core-collapse, asymmetric explosions, and various binary evolution scenarios may increase the initial rotation rates of many NSs.

scholarly journals Accretion onto Magnetized Neutron Stars: Polar Cap Flow and Centrifugally Driven Winds

1987 ◽  
Vol 125 ◽  
pp. 207-225
Author(s):  
Jonathan Arons
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Neutron Stars ◽  
Orbital Evolution ◽  
Time Dependent ◽  
Polar Cap ◽  
Periodic Oscillations ◽  
X Ray ◽  
Polar Caps ◽  
Basic Concepts

Some basic concepts of accretion onto the polar caps of magnetized neutron stars are reviewed. Preliminary results of new, multidimensional, time–dependent calculations of polar cap flow are outlined, and are used to suggest the possible observability of fluctuations in the X–ray intensity of accretion powered pulsars on time scales of 10–100 msec. The possible relevance of such fluctuations to Quasi–Periodic oscillations is suggested. Basic concepts of the interaction between a disk and the magnetosphere of a neutron star are also discussed. Some recent work on the disk–magnetosphere interaction is outlined, leading to the suggestion that a neutron star can lose angular momentum by driving some or all of the mass in the disk off as a centrifugally driven wind. The relevance of such mass loss to the orbital evolution of the binary is pointed out.

scholarly journals Anisotropic Heat Transfer Inside Rotating Neutron Stars

2004 ◽  
Vol 218 ◽  
pp. 39-40
Author(s):  
C. Y. Hui ◽  
K. S. Cheng
Keyword(s):  
Heat Transfer ◽  
Neutron Star ◽  
Simple Model ◽  
Neutron Stars ◽  
Slow Rotation ◽  
Spherically Symmetric ◽  
Transient Energy ◽  
Heat Transport Equation ◽  
Heat Pulses ◽  
Spherically Symmetric Metric

We have developed the anisotropic heat transport equation for rotating neutron stars. With a simple model of neutron star, we also model the propagation of heat pulses resulting from transient energy releases inside the star. Even in the slow rotation limit, the results with rotational effects involved could differ significantly from those obtained with a spherically symmetric metric in the timescale of the thermal afterglow.

scholarly journals On the spin-up events and spin direction of the X-ray pulsar GX 301-2

2020 ◽  
Vol 496 (3) ◽  
pp. 3991-3995
Author(s):  
Jiren Liu
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Orbital Motion ◽  
Low Energy ◽  
Slow Rotation ◽  
Scattering Process ◽  
X Ray ◽  
Spin Reversal ◽  
Stream Model ◽  
Orbital Spin

ABSTRACT Recently, a retrograde neutron star is proposed for the classical wind-fed X-ray pulsar, GX 301-2, to explain the orbital spin-up to spin-down reversal near periastron, based on the stream model invoked to explain the pre-periastron flare of GX 301-2 previously. We study in detail three rare spin-up events detected by Fermi/GBM and find that the spin derivatives are correlated with the Swift/BAT fluxes, following a relation of $\dot{\nu }\propto F^{0.75\pm 0.05}$. All the spin-up events of GX 301-2 started about 10 d after the periastron, which is the time needed for tidally stripped gas to reach the neutron star. The slow rotation of the optical companion implies that the accreted matter is likely to have angular momentum in the direction of the orbital motion, as in a Roche lobe-like overflow. As a result, the spin-up events of GX 301-2 would favour accretion of a prograde disc to a prograde neutron star. We also find that the flare of intrinsic X-ray emission of GX 301-2 happened 0.4 d before periastron, while the flare of low-energy emission (2–10 keV) happened about 1.4 d before periastron. The preceding low-energy flare can be explained by stronger absorption of the intrinsic X-ray emission closer to the periastron. This finding weakened the need of the stream model. The pulse fraction of GX 301-2 near periastron is reduced heavily, which is likely caused by Compton-scattering process. Compton reflection from the optical companion might be responsible for the observed orbital spin reversal of GX 301-2.

scholarly journals Magnetic and rotational quenching of the Λ effect

2019 ◽  
Vol 622 ◽  
pp. A195 ◽  
Author(s):  
P. J. Käpylä
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Differential Rotation ◽  
Large Scale ◽  
Turbulent Transport ◽  
Vertical Direction ◽  
Slow Rotation ◽  
Rapid Rotation ◽  
Maxwell Stresses

Context. Differential rotation in stars is driven by the turbulent transport of angular momentum.Aims. Our aim is to measure and parameterize the non-diffusive contribution to the total (Reynolds plus Maxwell) turbulent stress, known as the Λ effect, and its quenching as a function of rotation and magnetic field.Methods. Simulations of homogeneous, anisotropically forced turbulence in fully periodic cubes are used to extract their associated turbulent Reynolds and Maxwell stresses. The forcing is set up such that the vertical velocity component dominates over the horizontal ones, as in turbulent stellar convection. This choice of the forcing defines the vertical direction. Additional preferred directions are introduced by the imposed rotation and magnetic field vectors. The angle between the rotation vector and the vertical direction is varied such that the latitude range from the north pole to the equator is covered. Magnetic fields are introduced by imposing a uniform large-scale field on the system. Turbulent transport coefficients pertaining to the Λ effect are obtained by fitting. The results are compared with analytic studies.Results. The numerical and analytic results agree qualitatively at slow rotation and low Reynolds numbers. This means that vertical (horizontal) transport is downward (equatorward). At rapid rotation the latitude dependence of the stress is more complex than predicted by theory. The existence of a significant meridional Λ effect is confirmed. Large-scale vorticity generation is found at rapid rotation when the Reynolds number exceeds a threshold value. The Λ effect is severely quenched by large-scale magnetic fields due to the tendency of the Reynolds and Maxwell stresses to cancel each other. Rotational (magnetic) quenching of Λ occurs at more rapid rotation (at lower field strength) in the simulations than in the analytic studies.Conclusions. The current results largely confirm the earlier theoretical results, and also offer new insights: the non-negligible meridional Λ effect possibly plays a role in the maintenance of meridional circulation in stars, and the appearance of large-scale vortices raises the question of their effect on the angular momentum transport in rapidly rotating stellar convective envelopes. The results regarding magnetic quenching are consistent with the strong decrease in differential rotation in recent semi-global simulations and highlight the importance of including magnetic effects in differential rotation models.

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