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arXiv 0905.1355gr-qcastro-ph.HEhep-th
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吸积盘的性质能区分重力星和黑洞吗?

Can accretion disk properties distinguish gravastars from black holes?

Tiberiu Harko, Zoltán Kovács, Francisco S. N. Lobo

摘要:

引力星是一种假想的天体,由暗能量凝聚体和各向异性物质的强关联薄壳层组成,被认为是广义相对论标准黑洞图像的替代。从观测上区分天体物理学上的黑洞和引力星是后一种理论模型的主要挑战。在静止和轴对称几何的背景下,区分引力星和黑洞的可能性是通过分别对旋转引力星和克尔型黑洞周围的薄吸积盘进行比较研究。在本文中,我们考虑吸积盘周围缓慢旋转引力星,所有的度规张量分量估计到二阶的角速度。由于外部几何形状的差异,这两类致密天体的盘的热力学和电磁特性(能流、温度分布和平衡辐射谱)是不同的,因此给出了明确的观测特征。除此之外,还表明吸积质量到辐射的转换效率总是小于黑洞的转换效率,即,重力星体提供了一种比黑洞更低效的将质量转换为辐射的机制。因此,这些观测特征提供了明确区分旋转引力星和克尔型黑洞的可能性。

英文摘要:

Gravastars, hypothetic astrophysical objects, consisting of a dark energy condensate surrounded by a strongly correlated thin shell of anisotropic matter, have been proposed as an alternative to the standard black hole picture of general relativity. Observationally distinguishing between astrophysical black holes and gravastars is a major challenge for this latter theoretical model. In the context of stationary and axially symmetrical geometries, a possibility of distinguishing gravastars from black holes is through the comparative study of thin accretion disks around rotating gravastars and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around slowly rotating gravastars, with all the metric tensor components estimated up to the second order in the angular velocity. Due to the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation is always smaller than the conversion efficiency for black holes, i.e., gravastars provide a less efficient mechanism for converting mass to radiation than black holes. Thus, these observational signatures provide the possibility of clearly distinguishing rotating gravastars from Kerr-type black holes.

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