The imitation game: Proca stars that can mimic the Schwarzschild shadow
The imitation game: Proca stars that can mimic the Schwarzschild shadow
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DOI：
10.1088/1475-7516/2021/04/051
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发表时间：
2021-02
影响因子：
6.4
通讯作者：
C. Herdeiro;Alexandre M. Pombo;E. Radu;P. Cunha;N. Sanchis-Gual
中科院分区：
文献类型：
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作者：
C. Herdeiro;Alexandre M. Pombo;E. Radu;P. Cunha;N. Sanchis-Gual
动态鲁棒的玻色子星 (BS) 能否产生模仿黑洞 (BH) 的（有效）阴影？我们专注于具有自由标量场或矢量场以及多项式或轴子自相互作用场的球形BS模型。 BH 阴影与光环 (LR) 的存在有关。对于产生迷你BS的自由玻色子场，众所周知，这些恒星可以变得超紧凑——即拥有LR——但仅限于微扰不稳定的解决方案。我们表明，即使考虑不同的自交互，情况仍然如此。然而，有效阴影可以以不同的方式出现：如果 BS 重现类时测地线最内层稳定圆形轨道 (ISCO) 的存在（对于质量为 M 的史瓦西 BH，位于 r ISCO = 6M 处），则 BH 周围的吸积流形态将被模仿，并且在天体物理环境中会出现有效阴影。尽管球形BS可以容纳稳定的类时圆形轨道，一直到它们的中心，我们表明沿着这样的轨道的角速度Ω可能在远离原点的地方有一个最大值，即RΩ；最近观察到这种规模在某些吸积流场景中模仿了 BH 的 ISCO。然后： (i) 对于自由标量场或具有四次自相互作用，仅对于扰动不稳定的 BS，R Ω ≠ 0； (ii) 对于更高标量的自交互，例如轴离子，对于微扰稳定的 BS 来说，R Ω ≠ 0 是可能的，但在探索的参数空间中没有找到 R Ω = 6M 的解； (iii) 但对于自由矢量场，产生普罗卡星，存在 R Ω ≠ 0 的微扰稳定解，对于特定解，实际上 R Ω = 6M。因此，动态鲁棒的球形普罗卡星在模仿游戏中取得了成功：它们可以在天体物理环境中模仿具有相同 M 的（近）平衡史瓦西 BH 的阴影，尽管没有 LR，至少在某些观测条件下，正如我们通过明确比较此类普罗卡星和史瓦西 BH 的透镜效应所证实的那样。
Can a dynamically robust bosonic star (BS) produce an (effective) shadow that mimics that of a black hole (BH)? We focus on models of spherical BSs with free scalar or vector fields, as well as with polynomial or axionic self-interacting fields. The BH shadow is linked to the existence of light rings (LRs). For free bosonic fields, yielding mini-BSs, it is known that these stars can become ultra-compact — i.e., possess LRs — but only for perturbatively unstable solutions. We show this remains the case even when different self-interactions are considered. However, an effective shadow can arise in a different way: if BSs reproduce the existence of an innermost stable circular orbit (ISCO) for timelike geodesics (located at r ISCO = 6M for a Schwarzschild BH of mass M), the accretion flow morphology around BHs is mimicked and an effective shadow arises in an astrophysical environment. Even though spherical BSs may accommodate stable timelike circular orbits all the way down to their centre, we show the angular velocity Ω along such orbits may have a maximum away from the origin, at R Ω; this scale was recently observed to mimic the BH's ISCO in some scenarios of accretion flow. Then: (i) for free scalar fields or with quartic self-interactions, R Ω ≠ 0 only for perturbatively unstable BSs; (ii) for higher scalar self-interactions, e.g. axionic, R Ω ≠ 0 is possible for perturbatively stable BSs, but no solution with R Ω = 6M was found in the parameter space explored; (iii) but for free vector fields, yielding Proca stars, perturbatively stable solutions with R Ω ≠ 0 exist, and indeed R Ω = 6M for a particular solution. Thus, dynamically robust spherical Proca stars succeed in the imitation game: they can mimic the shadow of a (near-)equilibrium Schwarzschild BH with the same M, in an astrophysical environment, despite the absence of a LR, at least under some observation conditions, as we confirm by explicitly comparing the lensing of such Proca stars and Schwarzschild BHs.