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1.
Evolution of neutron star magnetic fields 总被引:2,自引:0,他引:2
Dipankar Bhattacharya 《Journal of Astrophysics and Astronomy》2002,23(1-2):67-72
This paper reviews the current status of the theoretical models of the evolution of the magnetic fields of neutron stars other
than magnetars. It appears that the magnetic fields of neutron stars decay significantly only if they are in binary systems.
Three major physical models for this, namely spindown-induced flux expulsion, ohmic evolution of crustal field and diamagnetic
screening of the field by accreted plasma, are reviewed. 相似文献
2.
V. V. Usov 《Astrophysics and Space Science》1988,140(1):39-47
During the evolution of the neutron star its magnetic field first decays exponentially with the time and then may becomes quasi-stationary. The non-decaying magnetic field of the neutron star is generated by a degenerate electron gas which is in the Landau orbital ferromagnetism (LOFER) state. Possibly, due to the neutron star transition into the LOFER state, magnetic fields remained sufficiently strong in the case of such old magnetic neutron stars as powerful X-ray sources (e.g., Her X-1), millisecond pulsars and the binary pulsar PSR 0655+64. 相似文献
3.
We adopt that in the interior of neutron stars both the proton and neutron superfluids are in the vortex state. Thus, in the superconducting core the magnetic field is expected to be organized in the form of quantized fluxoids. It is shown that fluxoids are buoyant. This gives rise to a rapid (5×104 yr) expulsion of the magnetic field out of the superconducting core to the subcrustal region, and a subsequent decay within the outer crust. The effect considered may be the physical reason why the characteristic decay-time of pulsar magnetic fields (106 yr) corresponds to the ohmic dissipation time within the neutron star crust. The intersection of two types of vortex lines with each other and its possible consequence for pulsars is briefly discussed. 相似文献
4.
L.W. Kebede 《Astrophysics and Space Science》2002,282(1):131-140
Plasma density gradient which is inherent to degenerate neutron star matter is shown to lead to large scale plasma diffusion
and subsequent charge separation. The surface (internal) fields generated by the spinning separated charges are found to be
dipolar with intensities of ≃ 1014 G (for the surface fields) very early in the life-time of a typical neutron star. The internal fields, on the other hand,
are relatively much weaker. These fields, which in this case are also shown to be temperature dependent, decay as a result
of neutrino and photon emissions. The decay law derived from equations of standard cooling calculations and the equation connecting
the magnetic field and temperature is indicated to have two distinct modes, each corresponding to the two branches of a typical
neutron star cooling curve. We have found that results derived from the decay law are consistent with observational findings.
Based on the theory behind our new model, we have also argued to show that isolated millisecond and sub-millisecond pulsars
might be very rare objects.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Z. F. Gao N. Wang D. L. Song J. P. Yuan C.-K. Chou 《Astrophysics and Space Science》2011,334(2):281-292
In this paper, an approximate method of calculating the Fermi energy of electrons (E
F
(e)) in a high-intensity magnetic field, based on the analysis of the distribution of a neutron star magnetic field, has been
proposed. In the interior of a neutron star, different forms of intense magnetic field could exist simultaneously and a high
electron Fermi energy could be generated by the release of magnetic field energy. The calculation results show that: E
F
(e) is related to density ρ, the mean electron number per baryon Y
e
and magnetic field strength B. 相似文献
6.
7.
G.A.J. Hussain 《Astronomische Nachrichten》2012,333(1):4-19
Stellar magnetic fields govern key aspects of the evolution of a young star, from controlling accretion to regulating the angular momentum evolution of the system. Spectro‐polarimetric studies of T Tauri stars have revealed a surprising range of magnetic field topologies. Meanwhile multi‐wavelength campaigns have probed T Tauri star systems from stellar photosphere to inner disk, allowing us to study magnetospheric accretion in unprecedented detail. We review recent results and discuss their implications for understanding the evolution of young stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
《天文和天体物理学研究(英文版)》2020,(2)
I present a novel mechanism to boost magnetic field amplification of newly born neutron stars in core collapse supernovae.In this mechanism,that operates in the jittering jets explosion mechanism and comes on top of the regular magnetic field amplification by turbulence,the accretion of stochastic angular momentum in core collapse supernovae forms a neutron star with strong initial magnetic fields but with a slow rotation.The varying angular momentum of the accreted gas,which is unique to the jittering jets explosion mechanism,exerts a varying azimuthal shear on the magnetic fields of the accreted mass near the surface of the neutron star.This,I argue,can form an amplifying effect which I term the stochastic omega(Sω) effect.In the common αω dynamo the rotation has constant direction and value,and hence supplies a constant azimuthal shear,while the convection has a stochastic behavior.In the Sω dynamo the stochastic angular momentum is different from turbulence in that it operates on a large scale,and it is different from a regular rotational shear in being stochastic.The basic assumption is that because of the varying direction of the angular momentum axis from one accretion episode to the next,the rotational flow of an accretion episode stretches the magnetic fields that were amplified in the previous episode.I estimate the amplification factor of the Sω dynamo alone to be ≈ 10.I speculate that the Sω effect accounts for a recent finding that many neutron stars are born with strong magnetic fields. 相似文献
9.
《New Astronomy》2019
Magnetic fields are observed in star forming regions. However simulations of the late stages of star formation that do not include magnetic fields provide a good fit to the properties of young stars including the initial mass function (IMF) and the multiplicity. We argue here that the simulations that do include magnetic fields are unable to capture the correct physics, in particular the high value of the magnetic Prandtl number, and the low value of the magnetic diffusivity. The artificially high (numerical and uncontrolled) magnetic diffusivity leads to a large magnetic flux pervading the star forming region. We argue further that in reality the dynamics of high magnetic Prandtl number turbulence may lead to local regions of magnetic energy dissipation through reconnection, meaning that the regions of molecular clouds which are forming stars might be essentially free of magnetic fields. Thus the simulations that ignore magnetic fields on the scales on which the properties of stellar masses, stellar multiplicities and planet-forming discs are determined, may be closer to reality than those which include magnetic fields, but can only do so in an unrealistic parameter regime. 相似文献
10.
V. K. Khersonskij 《Astrophysics and Space Science》1984,98(2):255-268
A two-dimensional potential energy surface of an H
2
+
molecular ion is calculated for the case of the strong magnetic field of the neutron starB=1011–1013 G. It is shown that the dependence of the potential energy from the angle between the magnetic field direction and the internuclear axis becomes very sharp as the magnetic field increases. The obtained potential energy surfaces can be used for studying the vibrational-rotational structure of the H
2
+
spectrum in a strong magnetic field and the development of the observational methods for the determination of the magnetic field of a neutron star. 相似文献
11.
The paper discusses the structure and energies of rotational-vibrational levels of a molecular ion H
2
+
in a strong magnetic field typical of neutron stars,B=1012–1013 G. The study is based on the calculations of the potential energy surface of this molecular ion presented in the paper by Khersonskii (1984a). The energies of the rovibrational levels are calculated with the aid of the perturbation theory. The number of levels in a H
2
+
potential hole is determined at different magnetic intensities. In particular, it is ascertained that the number of levels decreases as the strength of the magnetic field increases. The effect of nuclear spins on the structure of the rotational levels is considered. 相似文献
12.
Daniel J. Price Matthew R. Bate 《Monthly notices of the Royal Astronomical Society》2008,385(4):1820-1834
We examine the effect of magnetic fields on star cluster formation by performing simulations following the self-gravitating collapse of a turbulent molecular cloud to form stars in ideal magnetohydrodynamics. The collapse of the cloud is computed for global mass-to-flux ratios of ∞, 20, 10, 5 and 3, i.e. using both weak and strong magnetic fields. Whilst even at very low strengths the magnetic field is able to significantly influence the star formation process, for magnetic fields with plasma β < 1 the results are substantially different to the hydrodynamic case. In these cases we find large-scale magnetically supported voids imprinted in the cloud structure; anisotropic turbulent motions and column density striations aligned with the magnetic field lines, both of which have recently been observed in the Taurus molecular cloud. We also find strongly suppressed accretion in the magnetized runs, leading to up to a 75 per cent reduction in the amount of mass converted into stars over the course of the calculations and a more quiescent mode of star formation. There is also some indication that the relative formation efficiency of brown dwarfs is lower in the strongly magnetized runs due to a reduction in the importance of protostellar ejections. 相似文献
13.
14.
In this paper we present a new result, namely that the primal magnetic field of the collapsed core during a supernova explosion will, as a result of the conservation of magnetic flux, receive a massive boost to more than 90 times its original value by the Pauli paramagnetization of the highly degenerate relativistic electron gas just after the formation of the neutron star. Thus, the observed super-strong magnetic field of neutron stars may originate from the induced Pauli paramagnetization of the highly degenerate relativistic electron gas in the interior of the neutron star. We therefore have an apparently natural explanation for the surface magnetic field of a neutron star. 相似文献
15.
The effect of proton superconductivity on the generation of a toroidal magnetic field inside a neutron star is examined. It
is shown that including the entrainment of superconducting protons by superfluid neutrons does not change the previously obtained
results. Proton superconductivity does influence the structure of the generated magnetic field since, over a time on the order
of 104–105 years, the magnetic field increases linearly with time and can exceed the first critical field for proton superconductivity.
The distribution of the stationary toroidal magnetic field inside a neutron star is also found. 相似文献
16.
A. I. Chugunov 《Monthly notices of the Royal Astronomical Society》2006,369(1):349-354
We study eigenmodes of acoustic oscillations of high multipolarity l ∼ 100–1000 and high frequency (∼100 kHz), localized in neutron star envelopes. We show that the oscillation problem is self-similar. Once the oscillation spectrum is calculated for a given equation of state (EOS) in the envelope and given stellar mass M and radius R , it can be rescaled to a star with any M and R (but the same EOS in the envelope). For l ≳ 300, the modes can be subdivided into the outer and inner ones. The outer modes are mainly localized in the outer envelope. The inner modes are mostly localized near the neutron drip point, being associated with the softening of the EOS after the neutron drip. We calculate oscillation spectra for the EOSs of cold-catalyzed and accreted matter and show that the spectra of the inner modes are essentially different. A detection and identification of high-frequency pressure modes would allow one to infer M and R and determine also the EOS in the envelope (accreted or ground state) providing a new, potentially powerful method to explore the main parameters and internal structure of neutron stars. 相似文献
17.
D. J. Mullan James MacDonald 《Monthly notices of the Royal Astronomical Society》2005,356(3):1139-1148
Spruit has shown that an astrophysical dynamo can operate in the non-convective material of a differentially rotating star as a result of a particular instability in the magnetic field (the Tayler instability). By assuming that the dynamo operates in a state of marginal instability, Spruit has obtained formulae which predict the equilibrium strengths of azimuthal and radial field components in terms of local physical quantities. Here, we apply Spruit's formulae to our previously published models of rotating massive stars in order to estimate Tayler dynamo field strengths. There are no free parameters in Spruit's formulae. In our models of 10- and 50-M⊙ stars on the zero-age main sequence, we find internal azimuthal fields of up to 1 MG, and internal radial components of a few kG. Evolved models contain weaker fields. In order to obtain estimates of the field strength at the stellar surface, we examine the conditions under which the Tayler dynamo fields are subject to magnetic buoyancy. We find that conditions for Tayler instability overlap with those for buoyancy at intermediate to high magnetic latitudes. This suggests that fields emerge at the surface of a massive star between magnetic latitudes of about 45° and the poles. We attempt to estimate the strength of the field which emerges at the surface of a massive star. Although these estimates are very rough, we find that the surface field strengths overlap with values which have been reported recently for line-of-sight fields in several O and B stars. 相似文献
18.
Leonard C. Rosen 《Astrophysics and Space Science》1969,5(2):150-170
The composition of neutron star atmospheres is calculated as a function of time including effects of diffusion, cooling and thermonuclear reactions. A seven-component nuclear reaction network with includes He4, C12, O16, Ne20, Mg24, Si28 and Fe56 is utilized. Neutron star models with different initial nuclear abundances are compared as to subsequent nucleosynthesis. It is found that the final abundances are independent of original composition assuming He4 as the major initial constituent. The final composition of the atmosphere is predominantly Fe56. Mass loss from an evolving neutron star is examined as a possible source of cosmic rays. It is found that a neutron star contributes only Fe56 significantly to the cosmic-ray spectrum. 相似文献
19.
Dipankar Bhattacharya 《Journal of Astrophysics and Astronomy》1995,16(2):217-232
Observational evidence, and theoretical models of the magnetic field evolution of neutron stars is discussed. Observational
data indicates that the magnetic field of a neutron star decays significantly only if it has been a member of a close interacting
binary. Theoretically, the magnetic field evolution has been related to the processing of a neutron star in a binary system
through the spin evolution of the neutron star, and also through the accretion of matter on the neutron star surface. I describe
two specific models, one in which magnetic flux is expelled from the superconducting core during spin-down, via a copuling
between Abrikosov fluxoids and Onsager-Feynman vortices; and another in which the compression and heating of the stellar crust
by the accreted mass drastically reduces the ohmic decay time scale of a magnetic field configuration confined entirely to
the crust. General remarks about the behaviour of the crustal field under ohmic diffusion are also made. 相似文献
20.
《天文和天体物理学研究(英文版)》2015,(9)
Rotochemical heating originates in the deviation from beta equilibrium due to spin-down compression, which is closely related to the dipole magnetic field. We numerically calculate the deviation from chemical equilibrium and thermal evolution of neutron stars with decaying magnetic fields. We find that the power-law long term decay of the magnetic field slightly affects the deviation from chemical equilibrium and surface temperature. However, the magnetic decay leads to older neutron stars that could have a different surface temperature with the same magnetic field strength. That is, older neutron stars with a low magnetic field(108G) could have a lower temperature even with rotochemical heating in operation, which probably explains the lack of other observations on older millisecond pulsars with higher surface temperature,except millisecond pulsar J0437–4715. 相似文献