Dynamically probing the dark side of globular clusters: from central black holes to the Milky Way halo

球状星团是由多达100万颗恒星组成的密集的古老(约120亿年)的集合，通过重力聚集在一起，通常发现于星系的外部。这种特性的结合使它们成为研究天体物理学中一些非常及时的问题的理想实验室。这项研究计划旨在利用银河系中的球状星团更好地了解黑洞的起源和演化，并绘制出我们银河系外围的神秘暗物质图。这将通过研究恒星在星团中的运动和位置来实现，这些星团受到不可见质量(黑洞和暗物质)通过引力的影响。 最近，恒星质量黑洞(质量高达太阳质量的几十倍)合并产生的引力波(“时空涟漪”)的历史性发现引发了许多问题，即这些黑洞(大质量恒星生命的最终产物)怎么会发现自己离得这么近。主要的假设之一是，封闭的双星黑洞系统是通过球状星系团致密核心的相互作用形成的。虽然这些密集星团中的相互作用可以用功能强大的计算机模拟，但进入计算的许多假设都是不确定的。这个研究计划的第一个目标是通过比较对恒星运动和位置的观测与更简单(但计算速度更快)的静态模型来推断黑洞和其他恒星残留物在星团中的含量。静态模型捕捉到恒星残留物和正常恒星之间的相互作用。这将为更密集的计算模拟提供重要的边界条件，并能够更可靠地估计球状星团中黑洞合并的产生。 鉴于球状星团的中心密度很高，它们还可能形成和藏匿所谓的“中等质量黑洞”(数百到数万个太阳质量)，这可能是所有大质量星系中心发现的超大质量黑洞成长过程中缺失的一环。该计划的第二部分将测试和应用新的快速“静态”模型，该模型对中心中等质量黑洞敏感。这些模型将面临对假定中等质量黑洞附近恒星运动的观测，以限制这些黑洞的存在。这些努力还将为未来一代仪器铺平道路，这些仪器将更灵敏地探测中等质量黑洞附近的恒星运动，如果它们存在的话。 该计划的第三部分将专注于球状星团外缘恒星的运动，这些星团对银河系中暗物质的分布(本身拥有关于暗物质性质的线索)很敏感。一种很有前途的推断银河系暗物质分布的方法将被开发出来，并通过对星团外部恒星的新观测进行测试。

Globular clusters are dense and old (~12 billion years) collections of up to a million stars held together by gravity and typically found in the outer parts of galaxies. This combination of properties makes them ideal laboratories to study some very timely questions in astrophysics. This research program aims to use globular clusters in the Milky Way to better understand the origin and evolution of black holes, and map the mysterious dark matter in the outskirts of our galaxy. This will be done by studying the motions and positions of stars within clusters, which are affected by the invisible mass (black holes and dark matter) through gravity. The recent historic discovery of gravitational waves (“ripples in space-time”) from merging stellar-mass black holes (with masses up to a few tens of solar masses) has led to many questions about how these black holes (the end products of a massive star's life) can find themselves in such close vicinity. One of the leading hypotheses is that close binary black hole systems form via interactions in the dense core of globular clusters. While these interactions in dense clusters over time can be modelled with powerful computers, many of the assumptions entering the calculations are uncertain. The first goal of this research program is to infer the content of black holes and other stellar remnants in clusters at the present day by comparing observations of stellar motions and positions with simpler (but faster to compute) “static” models that capture the interplay between stellar remnants and normal stars. This will provide important boundary conditions for more computationally intensive simulations and enable more reliable estimates of the production of black hole mergers in globular clusters. Given their high central densities, globular clusters may also form and harbour so-called “intermediate-mass black holes” (several hundred to tens of thousands of solar masses), a possible missing link in the growth of the supermassive black holes found at the centre of all massive galaxies. The second component of this program will test and apply new fast “static” models sensitive to a central intermediate-mass black hole. The models will be confronted to observations of stellar motions in the vicinity of a putative intermediate-mass black holes to constrain the existence of these black holes. These efforts will also pave the way for the future generation of instruments that will probe more sensitively the motion of stars in the vicinity of intermediate-mass black holes, should they exist. The third component of the program will focus on the motions of stars at outer edges of globular clusters, which are sensitive to the distribution of dark matter in the Milky Way (itself holding clues about the nature of dark matter). A promising method for inferring the dark matter distribution in the Milky Way will be developed and tested with new observations of stars in the outer parts of clusters.