The Spin Parameter of Uniformly Rotating Compact Stars

Lo, Ka-Wai; Lin, Lap‐Ming

doi:10.1088/0004-637x/728/1/12

Cited by 103 publications

(117 citation statements)

References 50 publications

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“…Interestingly, for κ = −1 and N = 3, not only does the first ergoregion solution appear before the point of maximum charge, but it occurs for a spin parameter large than one. High spin parameters, although fairly common for planets and nuclear stars, are quite rare to achieve with compact objects, for instance rapidly rotating neutron stars are usually bound by a * ≤ 0.7, while the more exotic quark stars could go beyond the unit slope [32].…”

Section: B N=3 Modelmentioning

confidence: 99%

Rotating tensor-multiscalar solitons

2020

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In the context of a special class of tensor-multi-scalar theories of gravity for which the target-space metric admits an isometry under which the theory is invariant, we present rotating vacuum solutions, namely with no matter fields. These objects behave like nontopological solitons, whose primary stability is due to the conserved charge arising from the global symmetry. We consider theories with two and three scalar fields, different Gauss curvatures and quartic interaction coefficients. As it occurs for boson stars, their angular momentum is quantized.

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Section: B N=3 Modelmentioning

confidence: 99%

Rotating tensor-multiscalar solitons

2020

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“…The Kerr parameter is important for neutrons stars and in general, compact objects. To be more specific, it can lead to possible limits for the compactness on neutron stars and consequently on the spin frequency, and second, can be a criteria for determining the final fate of the collapse of a rotating compact star [31,42]. The relation which describes the Kerr parameter [31] is…”

Section: Kerr Parametermentioning

confidence: 99%

Speed of sound constraints on maximally rotating neutron stars

2020

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The observation of maximally-rotating neutron stars (in comparison with non-rotating ones) may provide more information on the behavior of nuclear matter at high densities. In the present work we provide a theoretical treatment concerning the effects of the upper bound of the sound speed in dense matter on the bulk properties of maximally-rotating (at mass-shedding limit) neutron stars. In particular, we consider two upper bounds for the speed of sound, vs = c and vs = c/ √ 3, and the one provided by the relativistic kinetic theory. We investigate to what extent the possible predicted (from various theories and conjectures) upper bounds on the speed of sound constrain the ones of various key quantities, including the maximum mass and the corresponding radius, Keplerian frequency, Kerr parameter and moment of inertia. We mainly focus on the lower proposed limit, vs = c/ √ 3, and we explore in which mass region a rotating neutron star collapses to a black hole. In any case, useful relations of the mentioned bulk properties with the transition density are derived and compared with the corresponding non-rotating cases. We concluded that the proposed limit vs = c/ √ 3 leads to dramatic decrease on the values of the maximum mass, Kerr parameter and moment of inertia preventing a neutron star to reach values which derived with the consideration of realistic equations of state or from other constraints. Possible measurements of the Kerr parameter and moment of inertia would shed light on these issues and help to reveal the speed of sound bound in dense matter.

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“…Lo & LIN (2011) has shown that j max ∼ 0.7 for neutron stars without hyperons, while the spin parameter of a quark star modeled by the MIT bag model can be larger than unity and does not have a universal upper bound. It is interesting to further explore what the key factor to determine the spin parameter is, and study the reliability of the result on various selected EOSs of dense matter, such as hyperonic NS and hybrid stars, which are not considered yet in Lo & LIN (2011). The calculations and the results for strange quark stars with the MIT bag model are very similar to those in Lo & LIN (2011), which have j max > 1 for most of star masses, thus we do not exhibit here.…”

Section: The Crust Effects On Dimensionless Spin Parametermentioning

confidence: 99%

“…In Kato (2008), based on a Resonantly Excited Disk-Oscillation Model, they suggested that the observed correlations in Cir X-1 could be well described by adopting M = 1.5 ∼ 2.0M ⊙ and j ∼ 0.8. Thus, Lo & LIN (2011) suggested the central star in Cir X-1 could be a quark star if assuming Kato's model is correct, due to the calculated uniformly rotating neutron stars with hadronic matter cannot have j > 0.7. However, in this work, we show that the j max of the traditional NS, hyperonic NS and hybrid stars are also larger than 0.7 if the crust structure is not included.…”

Section: The Crust Effects On Dimensionless Spin Parametermentioning

confidence: 99%

A key factor to the spin parameter of uniformly rotating compact stars: crust structure

Zhang

Sun

et al. 2016

Res. Astron. Astrophys.

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Aims. We study the key factor to determine the dimensionless spin parameter j ≡ cJ/(GM 2 ) of different kinds of uniformly rotating compact stars, including the traditional neutron stars, hyperonic neutron stars, and hybrid stars, and check the reliability of the results on various types of equations of state of dense matter.Methods. The equations of state from the relativistic mean field theory and the MIT bag model are adopted to simulate compact stars. Numerical calculations of rigidly rotating neutron stars are performed using the RNS code in the framework of general relativity by solving the Einstein equations for stationary axis-symmetric spacetime. Results. The crust structure of compact stars is found to be a key factor to determine the maximum value of the spin parameter j max . For the stars with inclusion of the crust, j max ∼ 0.7 is sustained for various kinds of compact stars with M > 0.5M ⊙ , and is found to be insensitive to the mass of star and selected equations of state. For the traditional neutron stars, hyperonic neutron stars and hybrid stars without crust structure, the value j max lies in the range of [0.7, 1.0]. Thus, not j > 0.7 but j > 1 could be treated as the candidate criterion to distinguish the strange quark stars from the other kinds of compact stars. Furthermore, a universal formulais suggested to calculate the spin parameter at any rotational frequency for all kinds of compact stars with crust structure and M > 0.5M ⊙ .

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The Spin Parameter of Uniformly Rotating Compact Stars

Cited by 103 publications

References 50 publications

Rotating tensor-multiscalar solitons

Rotating tensor-multiscalar solitons

Speed of sound constraints on maximally rotating neutron stars

A key factor to the spin parameter of uniformly rotating compact stars: crust structure

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