通过中子星的“重力化学加热”来约束引力常量的可能的时间变化
Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
摘要：
假设引力常量$G$随时间的变化会使中子星膨胀或收缩，因此它们内部的物质会偏离β平衡。这引起了非平衡弱反应，释放的能量部分用于中微子发射，部分用于内部加热。最终，恒星到达一个温度几乎保持不变的静止状态，因为通过$G$变化的强迫被正在进行的反应所平衡。使用最近的毫秒脉冲星（PSR J0437 $-$ 4715）的表面温度推断从紫外线观测和热演化的理论模型的结果，我们估计这种变化的两个上限：（1）$|\dot G/G| < 2 \times 10^{-10}\mathrm{yr}^{-1},$，如果快速，“直接Urca”的反应是允许的，（2）$|\dot G/G|<4\times 10^{-12}\mathrm{yr}^{-1},$只考虑较慢的，“修改Urca”的反应。后者是通过其他方法获得的最严格的上限之一。
英文摘要：
A hypothetical time-variation of the gravitational constant $G$ would make neutron stars expand or contract, so the matter in their interiors would depart from beta equilibrium. This induces non-equilibrium weak reactions, which release energy that is invested partly in neutrino emission and partly in internal heating. Eventually, the star arrives at a stationary state in which the temperature remains nearly constant, as the forcing through the change of $G$ is balanced by the ongoing reactions. Using the surface temperature of the nearest millisecond pulsar (PSR J0437$-$4715) inferred from ultraviolet observations and results from theoretical modelling of the thermal evolution, we estimate two upper limits for this variation: (1) $|\dot G/G| < 2 \times 10^{-10}\mathrm{yr}^{-1},$ if the fast, "direct Urca" reactions are allowed, and (2) $|\dot G/G|<4\times 10^{-12}\mathrm{yr}^{-1},$ considering only the slower, "modified Urca" reactions. The latter is among the most restrictive upper limits obtained by other methods.
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