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arXiv 1109.4149astro-ph.HEastro-ph.COastro-ph.GAgr-qc
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低相对论性angular momentum吸积的Blandford-Znajek机制的效率

On the efficiency of the Blandford-Znajek mechanism for low angular momentum relativistic accretion

Tapas K. Das, Bozena Czerny

摘要:

在文献中,Blandford-Znajek(BZ)机制通常被研究为具有相当高的角动量的吸积,导致形成冷的开普勒盘,或者如ADAF/RIAF框架内所描述的热的和几何厚的亚开普勒流。然而,在附近的椭圆星系,以及我们自己的银河系中心,吸积非常低的角动量是普遍的。这种准球形强次开普勒吸积具有复杂的动力学特征,可以容纳定常激波。在这封信中,我们提出了我们的计算的最大效率可通过BZ机制的完整的广义相对论性弱旋转轴对称流在克尔度规。本文详细研究了旋转和反向旋转吸积的激波和激波自由流动。这样的研究在文献中从未做过。我们发现,能量提取效率是低的,约0.1%,并增加了一个因素15,如果包括冲压压力。这种效率仍然比这种光学薄流的辐射效率高得多。对于BZ机制,冲击流比无冲击流产生更高的效率,而逆行流提供的效率值略大于逆行流。

英文摘要:

Blandford-Znajek (BZ) mechanism has usually been studied in the literature for accretion with considerably high angular momentum leading either to the formation of a cold Keplerian disc, or a hot and geometrically thick sub-Keplerian flow as described within the framework of ADAF/RIAF. However, in nearby elliptical galaxies, as well as for our own Galactic centre, accretion with very low angular momentum is prevalent. Such quasi-spherical strongly sub-Keplerian accretion has complex dynamical features and can accommodate stationary shocks. In this letter, we present our calculation for the maximum efficiency obtainable through the BZ mechanism for complete general relativistic weakly rotating axisymmetric flow in the Kerr metric. Both shocked and shock free flow has been studied in detail for rotating and counter rotating accretion. Such study has never been done in the literature before. We find that the energy extraction efficiency is low, about 0.1%, and increases by a factor 15 if the ram pressure is included. Such an efficiency is still much higher than the radiative efficiency of such optically thin flows. For BZ mechanism, shocked flow produces higher efficiency than the shock free solutions and retrograde flow provides a slightly larger value of the efficiency than that for the prograde flow.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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