Physics of Accretion Disks Around Black Holes

Ast0205806Krolike黑洞是非常强大的光源。总体而言，宇宙中黑洞产生的总光能几乎与恒星产生的光能一样多。然而，黑洞能够辐射如此多的光的机制多年来一直是个谜。这个谜团的根本原因是，在没有摩擦力的情况下，围绕大质量物体的轨道上的物质将永远不停地旋转，根本不会释放任何能量。除了紧靠其边缘的区域外，这条规则对黑洞和对普通物体一样适用。因为普通粘性引起的摩擦力太弱，无法解释观测到的黑洞吞噬质量的速度；这种摩擦力的来源几十年来一直是个谜。然而，在20世纪90年代，我们逐渐相信了曾经的推测，即纠缠的磁场会在吸积物质中自发地增强强度，它们所产生的力将足够强大，以提供必要的“摩擦”。由于纠缠的磁场力的计算非常复杂，它们必须通过大型计算机模拟来完成。这个项目将进行一个连贯的大规模数值模拟项目，目标有两个：a)计算磁力如何控制黑洞吸积过程中释放的能量总量；b)展示释放的能量如何转化为热量，然后是我们所看到的光。

AST 0205806KrolikBlack holes are tremendously powerful sources of light. In aggregate, the total light power produced by black holes in the Universe is almost as much as that generated by stars. However, the mechanism by which black holes are able to radiate so much light has remained mysterious for many years. The fundamental reason for this mystery is that, without friction, matter in orbit around a massive object would go round and round forever, and no energy would be released at all. Except for the region immediately outside its edge, this rule is as true for a black hole as for an ordinary object. Because friction caused by ordinary viscosity is far too weak to account for the observed rate at which mass is swallowed by black holes; the source of this friction had been a mystery for decades. During the 1990s, however, we gradually gained confidence in what was once the speculative suggestion that tangled magnetic fields would spontaneously grow in strength in accreting matter, and the forces they create would be strong enough to provide the necessary "friction".Since calculations of tangled magnetic field forces are very complex they must be done with large computer simulations. This project will conduct a coherent program of large-scale numerical simulations with a pair of goals: a) to compute how the magnetic forces control the total amount of energy released in black hole accretion; and b) to show how the released energy finds its way into heat, and then the light that we see.***