On the absence of winds in advection-dominated accretion flows
On the absence of winds in advection-dominated accretion flows
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DOI：
10.1046/j.1365-8711.2000.03406.x
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发表时间：
2000-06
影响因子：
4.8
通讯作者：
M. Abramowicz;J. Lasota;I. Igumenshchev
中科院分区：
文献类型：
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作者：
M. Abramowicz;J. Lasota;I. Igumenshchev
摘要：我们表明，最近发表的关于平流主导的吸积流（ADAFs）需要强风存在的断言是没有根据的，因为它们假设以低速率吸积到黑洞的流的低辐射效率意味着通过流的径向能量和角动量通量消失（这也用“伯努利函数”表示为正）。然而，这只是自相似解的一个性质，它不能充分表示全局吸积流。我们回顾了吸积流到黑洞的一般性质，并表明这种必然是跨音速的流动可能具有d正或负伯努利函数，这取决于流动粘度。低粘度流动（a-粘度模型中为0:1）具有负伯努利函数。迄今为止，所有低粘度流的二维和一维数值模型无一例外地没有明显的流出。在高粘度下，流出的存在取决于假定的粘度、状态方程和外边界条件。在这种情况下调用的伯努利函数的正号与流出的存在无关。作为一个例子，我们回想起具有中等粘度的二维数值模型，它具有正的伯努利函数值，并且没有流出。因此，从这个角度来看，ADAFs与薄的开普勒盘没有什么不同：它们可能有强风，但不一定有强风。
ABSTRA C T We show that recently published assertions that advection-dominated accretion flows (ADAFs) require the presence of strong winds are unfounded because they assume that low radiative efficiency in flows accreting at low rates on to black holes implies vanishing radial energy and angular momentum fluxes through the flow (which is also formulated in terms of the ‘Bernoulli function’ being positive). This, however, is a property only of self-similar solutions which are an inadequate representation of global accretion flows. We recall general properties of accretion flows on to black holes and show that such, necessarily transonic, flows may have either d positive or negative Bernoulli function depending on the flow viscosity. Flows with low viscosities Oa & 0:1 in the a-viscosity model) have a negative Bernoulli function. Without exception, all 2D and 1D numerical models of low-viscosity flows constructed to date experience no significant outflows. At high viscosities the presence of outflows depends on the assumed viscosity, on the equation of state and on the outer boundary condition. The positive sign of the Bernoulli function invoked in this context is irrelevant to the presence of outflows. As an illustration, we recall 2D numerical models with moderate viscosity that have positive values of the Bernoulli function and experience no outflows. ADAFs, therefore, do not differ from this point of view from thin Keplerian discs: they may have, but they do not have to have, strong winds.