标题： 大麦哲伦星系引力微透镜结果：它们意味着什么？ 显示英文标题

标题： Magellanic Cloud Gravitational Microlensing Results: What Do They Mean?

摘要： 我回顾了对大麦哲伦星云的引力微透镜调查的最新结果。 MACHO和EROS-1调查的联合微透镜光学深度为tau_LMC = 2.1{+1.3/-0.8}* 10^{-7}，这明显大于由已知恒星引起的tau < 0.5* 10^{-7}的背景，但低于由完全由Macho组成的晕层预期的微透镜光学深度tau = 4.7*10^{-7}。 这一结果最简单的解释是，几乎一半的暗晕由典型质量约为0.5 Msun的Macho组成。 这些Macho可能是古老的白矮星，但显然无法确定在这些白矮星之前的恒星形成过程是否可能未被探测到。 也许，Macho可能是非重子的，但目前还没有令人信服的非重子Macho形成模型。 因此，一些作者尝试开发替代模型，试图用非晕层透镜来解释LMC的微透镜结果。 这些模型中的许多都假设了之前未知的暗恒星种群，它们对银河系的总质量有显著贡献，因此只是暗物质解决方案的简单变体。 然而，假设在视线方向上存在一个未知的矮星系或对LMC的扭曲显著增强了LMC自透镜光学深度的模型，可以用少量的质量潜在地解释LMC的透镜结果，因此这些可以被视为真正的非暗物质解决方案来解决Macho之谜。 迄今为止提出的所有此类模型都有严重的问题，因此目前尚无令人信服的替代暗物质解释。 然而，这个问题可以通过一个比当前微透镜调查更灵敏的第二代引力微透镜调查来观测解决。 显示英文摘要

摘要： I review recent results from gravitational microlensing surveys of the Large Magellanic Cloud. The combined microlensing optical depth of the MACHO and EROS-1 surveys is tau_LMC = 2.1{+1.3/-0.8}* 10^{-7} which is substantially larger than the background of tau < 0.5* 10^{-7} from lensing by known stars but is below the expected microlensing optical depth of tau = 4.7*10^{-7} for a halo composed entirely of Machos. The simplest interpretation of this result is that nearly half of the dark halo is composed of Machos with a typical mass of order 0.5 Msun. These Machos could be old white dwarfs, but it is not obvious that the generation of stars that preceded these white dwarfs could have gone undetected. Perhaps, the Machos could be non-baryonic, but there is no compelling model for the formation of non-baryonic Machos. Therefore, some authors have tried to develop alternative models which attempt to explain the LMC microlensing results with non-halo lenses. Many of these models postulate previously unknown dark stellar populations which contribute significantly to the total mass of the Galaxy and are therefore simply variations of the dark matter solution. However, models which postulate an unknown dwarf galaxy along the line of sight to the LMC or a distortion of the LMC which significantly enhances the LMC self-lensing optical depth can potentially explain the LMC lensing results with only a small amount of mass, so these can be regarded as true non-dark matter solutions to the Macho puzzle. All such models that have been proposed so far have serious problems, so there is as yet no compelling alternative to the dark matter interpretation. However, the problem can be solved observationally with a second generation gravitational microlensing survey that is significantly more sensitive than current microlensing surveys.