标题： 用S2恒星轨道限制银河系中心的爱因斯坦-麦克斯韦-标量-轴子黑洞 显示英文标题

标题： Constraining an Einstein-Maxwell-dilaton-axion black hole at the Galactic Center with the orbit of the S2 star

摘要： 我们通过研究S2星在银河系中心的测地线运动，得到了爱因斯坦-麦克斯韦-标量-轴子引力中球对称黑洞解中的标量参数的新约束。 爱因斯坦-麦克斯韦-标量-轴子黑洞代表了广义相对论中标准黑洞范式的引人注目的替代方案。 该理论源自异弦理论的低能有效作用，并已被证明能够从黑洞阴影的直接成像中预测出独特的观测特征。 在本质上，爱因斯坦-麦克斯韦-标量-轴子包含了额外的电磁场、标量场和轴子场，这些场耦合到时空度规。 当考虑带电非旋转黑洞解时，额外的场使度规增加了一个新的参数$b$，称为标量参数，理论上它被限制在$0<b<M$。 利用公开可用的S2的天体测量数据，我们在95%置信水平上得出了$b\lesssim 12M$的上限，并证明仅测量S2的相对论轨道进动就足以将这个界限缩小到$b\lesssim 1.4M$的同一置信水平。 此外，使用模拟 GRAVITY 干涉仪未来观测S2的假想数据，我们表明改进的天体测量精度可以帮助在监测S2轨道一个半周期后进一步缩小允许的标量参数范围至$b\lesssim0.033M$。 显示英文摘要

摘要： We derive new constraints on the dilaton parameter appearing in the spherically-symmetric black hole solution of Einstein-Maxwell-dilaton-axion gravity, by studying the geodesic motion of the S2 star in the Galactic Center. Einstein-Maxwell-dilaton-axion black holes represent a compelling alternative to the standard black hole paradigm in General Relativity. This theory emerges from the low energy effective action of the heterotic string theory and has been proven to predict peculiar observational features from the direct imaging of black hole shadows. At a fundamental level, Einstein-Maxwell-dilaton-axion includes additional electromagnetic, dilatonic and axionic fields coupled to the space-time metric. When considering charged non-rotating black hole solutions, the additional fields endow the metric with one extra parameter $b$, called dilaton parameter, that is theoretically bound to $0<b<M$. Using publicly available astrometric data for S2 we derive an upper bound on $b\lesssim 12M$ at 95% confidence level and we demonstrate that only including the measurement of the relativistic orbital precession for S2 is sufficient to reduce this bound to $b\lesssim 1.4M$ at the same confidence level. Additionally, using a mock data mimicking future observations of S2 with the GRAVITY interferometer, we show that improved astrometric precision can help further narrow down the allowed dilaton parameter range to $b\lesssim0.033M$ after monitoring the S2 orbit for one and a half period.