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arXiv 0906.0096gr-qc
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中子星的相对论潮汐性质

Relativistic tidal properties of neutron stars

Thibault Damour, Alessandro Nagar

摘要:

我们研究了中子星对外部相对论潮汐场的各种线性响应。重点讨论了三种不同的潮汐响应,它们对应于三种不同的潮汐系数:(1)重电型系数Gμ_ \ell =[length]^{2 \ell +1},测量由外部\ell^{th}级重电潮汐场G_{a_1... a_\ell}在恒星中引起的\ell^{th}级质量多极矩GM_{a_1... a_\ell};(ii)重磁型系数Gσ_ \ell =[长度]^{2 \ell +1},测量由外部\ell^{th}级重磁潮汐场H_{a_1... a_\ell}在恒星中诱导的\ell^{th}自旋多极矩G S_{a_1... a_\ell};以及(iii)无量纲的"形状“洛夫数h_ \ell,它测量恒星表面形状因外部\ell^{th}级重力-电力潮汐场而产生的变形。所有的无量纲潮汐系数Gμ_ \ell /R^{2 \ell +1},Gσ_r/R^{2 \ell +1}和h_ \ell(其中R是恒星的半径)都对恒星的"紧致度“c \equiv GM/(c_0^2 R)(其中我们用c_0表示光速)的值有很强的敏感性。特别地,当c被形式地扩展到“黑洞(BH)极限”c^{BH}=1/2时,发现Gμ_k/R^{2 π +1} \sim k_ \ell随着c的增加而强烈地减小,直到零值。形状Love数h_ \ell随着c的增大而显著减小,但它在形式极限c \to c^{BH}中并不为零.μ_ \ell和σ_ \ell在形式上消失为c \to c^{BH}是黑洞无毛性质的结果;这表明,但决不证明,描述黑洞引力相互作用的有效作用量可能不需要用非最小世界线耦合来扩充。

英文摘要:

We study the various linear responses of neutron stars to external relativistic tidal fields. We focus on three different tidal responses, associated to three different tidal coefficients: (i) a gravito-electric-type coefficient Gμ_\ell=[length]^{2\ell+1} measuring the \ell^{th}-order mass multipolar moment GM_{a_1... a_\ell} induced in a star by an external \ell^{th}-order gravito-electric tidal field G_{a_1... a_\ell}; (ii) a gravito-magnetic-type coefficient Gσ_\ell=[length]^{2\ell+1} measuring the \ell^{th} spin multipole moment G S_{a_1... a_\ell} induced in a star by an external \ell^{th}-order gravito-magnetic tidal field H_{a_1... a_\ell}; and (iii) a dimensionless ``shape'' Love number h_\ell measuring the distortion of the shape of the surface of a star by an external \ell^{th}-order gravito-electric tidal field. All the dimensionless tidal coefficients Gμ_\ell/R^{2\ell+1}, Gσ_ł/R^{2\ell+1} and h_\ell (where R is the radius of the star) are found to have a strong sensitivity to the value of the star's ``compactness'' c\equiv GM/(c_0^2 R) (where we indicate by c_0 the speed of light). In particular, Gμ_ł/R^{2ł+1}\sim k_\ell is found to strongly decrease, as c increases, down to a zero value as c is formally extended to the ``black-hole (BH) limit'' c^{BH}=1/2. The shape Love number h_\ell is also found to significantly decrease as c increases, though it does not vanish in the formal limit c\to c^{BH}. The formal vanishing of μ_\ell and σ_\ell as c\to c^{BH} is a consequence of the no-hair properties of black holes; this suggests, but in no way proves, that the effective action describing the gravitational interactions of black holes may not need to be augmented by nonminimal worldline couplings.

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