标题： 回溯MACHOs：虚幻的希望？ 显示英文标题

标题： Retro-MACHOs: Pi in the sky?

摘要： 用一束手电筒的光照射黑洞，人们会看到一系列同心光环的回归。 对于一个点光源，以及透镜、光源和观察者之间的完美对齐，这些光环的亮度将是无限的（在几何光学极限下）。 通过这种方式，遥远的黑洞可以通过它们对太阳光的反射而被揭示出来。 这种反向MACHO事件涉及光子离开太阳，在黑洞周围完成π旋转，然后返回地球被探测到。 我们的计算表明，尽管光的返回非常微弱，但对于位于我们太阳系边缘的恒星级黑洞，它仍可能被检测到。 例如，所有质量为M或更大的（未被遮挡的）黑洞将在以下距离范围内以极限星等m被观测到：0.02 pc x\sqrt[3]{10^{(m-30)/2.5} (M/10 M_sun)^2}。 发现一个反向MACHO提供了一种直接成像黑洞存在的方法，并且将是强场广义相对论的一个令人震惊的确认。 显示英文摘要

摘要： Shine a flashlight on a black hole, and one is greeted with the return of a series of concentric rings of light. For a point source of light, and for perfect alignment of the lens, source, and observer, the rings are of infinite brightness (in the limit of geometric optics). In this manner, distant black holes can be revealed through their reflection of light from the Sun. Such retro-MACHO events involve photons leaving the Sun, making a Pi rotation about the black hole, and then returning to be detected at the Earth. Our calculations show that, although the light return is quite small, it may nonetheless be detectable for stellar-mass black holes at the edge of our solar system. For example, all (unobscured) black holes of mass M or greater will be observable to a limiting magnitude m, at a distance given by: 0.02 pc x \sqrt[3]{10^{(m-30)/2.5} (M/10 M_sun)^2}. Discovery of a Retro-MACHO offers a way to directly image the presence of a black hole, and would be a stunning confirmation of strong-field general relativity.