Innermost stable circular orbits and epicyclic frequencies around a magnetized neutron star

Gutiérrez-Ruiz, Andrés F.; Valenzuela-Toledo, César A.; Pachón, Leonardo A.

doi:10.11144/javeriana.sc19-1.isco

Cited by 4 publications

(8 citation statements)

References 35 publications

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“…Kluźniak et al 1990;Shibata & Sasaki 1998;Pachón et al 2006Pachón et al , 2012Bakala et al 2012;Gutierrez et al 2013). It has been shown that for geodesic motion, these are well described by formulae derived considering NS spacetime approximated by the Hartle-Thorne metric (Hartle & Thorne 1968;Abramowicz et al 2003;Berti et al 2005).…”

Section: Behaviour Of Isco Radius and Ns Compactnessmentioning

confidence: 82%

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

Török

Urbanec

Adámek

et al. 2014

A&A

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The innermost stable cicular orbit (ISCO) of an accretion disc that orbits a neutron star (NS) is often assumed to be a unique prediction of general relativity. However, it has been argued that ISCO also appears around highly elliptic bodies described by Newtonian theory. In this sense, the behaviour of an ISCO around a rotating oblate neutron star is formed by the interplay between relativistic and Newtonian effects. Here we briefly explore the consequences of this interplay using a straightforward analytic approach as well as numerical models that involve modern NS equations of state. We examine the ratio K between the ISCO radius and the radius of the neutron star. We find that, with growing NS spin, the ratio K first decreases, but then starts to increase. This non-monotonic behaviour of K can give rise to a neutron star spin interval in which ISCO appears for two very different ranges of NS mass. This may strongly affect the distribution of neutron stars that have an ISCO (ISCO-NS). When (all) neutron stars are distributed around a high mass M 0 , the ISCO-NS spin distribution is roughly the same as the spin distribution corresponding to all neutron stars. In contrast, if M 0 is low, the ISCO-NS distribution can only have a peak around a high value of spin. Finally, an intermediate value of M 0 can imply an ISCO-NS distribution divided into two distinct groups of slow and fast rotators. Our findings have immediate astrophysical applications. They can be used for example to distinguish between different models of high-frequency quasiperiodic oscillations observed in low-mass NS X-ray binaries.

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Section: Behaviour Of Isco Radius and Ns Compactnessmentioning

confidence: 82%

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

Török

Urbanec

Adámek

et al. 2014

A&A

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“…7 depicts the functional dependence on ζ, as in the case analyzed in Ref. [40], the Keplerian frequency increases with increasing ζ because the ISCO's radius decreases (see Fig. 6) as a consequence of the additional deformation of the space-time by the electromagnetic field.…”

Section: Influence Of the Electromagnetic Field In The Keplerian And mentioning

confidence: 84%

“…By combining the facts that (i) almost all the analytic closed form models for relevant astrophysical objects have been conceived in the frame of stationary axisymmetry geometry (see [40][41][42][43][44][45] for the case of neutron stars), (ii) powerful tools to construct exact solution to the Einstein-Maxwell field equation have been developed, e.g. [46][47][48], and (iii) systematic studies on the construction of exact solution from its physical content have been performed [49,50], a new analytic exact solution to the Einstein-Maxwell field equations is introduced below.…”

Section: Analytic Formulae Of the Modelmentioning

confidence: 99%

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Electromagnetically induced frame dragging around astrophysical objects

Gutiérrez-Ruiz

Pachón

2015

Phys. Rev. D

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Frame dragging (Lense-Thirring effect) is generally associated with rotating astrophysical objects. However, it can also be generated by electromagnetic fields if electric and magnetic fields are simultaneously present. In most models of astrophysical objects, macroscopic charge neutrality is assumed and the entire electromagnetic field is characterized in terms of a magnetic dipole component. Hence, the purely electromagnetic contribution to the frame dragging vanishes. However, strange stars may possess independent electric dipole and neutron stars independent electric quadrupole moments that may lead to the presence of purely electromagnetic contributions to the frame dragging. Moreover, recent observations have shown that in stars with strong electromagnetic fields, the magnetic quadrupole may have a significant contribution to the dynamics of stellar processes. As an attempt to characterize and quantify the effect of electromagnetic frame-dragging in these kind of astrophysical objects, an analytic solution to the Einstein-Maxwell equations is constructed here on the basis that the electromagnetic field is generated by the combination of arbitrary magnetic and electric dipoles plus arbitrary magnetic and electric quadrupole moments. The effect of each multipole contribution on the vorticity scalar and the Poynting vector is described in detail. Corrections on important quantities such the innermost stable circular orbit (ISCO) and the epicyclic frequencies are also considered.

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“…Interestingly, the conversion efficiency decreases due to the presence of the magnetic fields and of the tidal perturbations. Alternative studies of the effects of the neutron star's magnetic field on the exterior metric and the position of ISCO's can be found in [132,133].…”

Section: Discussion and Final Remarksmentioning

confidence: 99%

Thin accretion disks around cold Bose–Einstein condensate stars

Dǎnilǎ

Harkó

Kovács³

2015

Eur. Phys. J. C

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Due to their superfluid properties some compact astrophysical objects, like neutron or quark stars, may contain a significant part of their matter in the form of a BoseEinstein condensate (BEC). Observationally distinguishing between neutron/quark stars and BEC stars is a major challenge for this latter theoretical model. An observational possibility of indirectly distinguishing BEC stars from neutron/quark stars is through the study of the thin accretion disks around compact general relativistic objects. In the present paper, we perform a detailed comparative study of the electromagnetic and thermodynamic properties of the thin accretion disks around rapidly rotating BEC stars, neutron stars and quark stars, respectively. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution, equilibrium radiation spectrum, and efficiency of energy conversion) are different for these classes of compact objects. Hence in this preliminary study we have pointed out some astrophysical signatures that may allow one to observationally discriminate between BEC stars and neutron/quark stars.

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Innermost stable circular orbits and epicyclic frequencies around a magnetized neutron star

Cited by 4 publications

References 35 publications

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

Electromagnetically induced frame dragging around astrophysical objects

Thin accretion disks around cold Bose–Einstein condensate stars

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