Hyper-velocity stars

我们建议研究新发现的超高速恒星群，以确定它们的真实性质。超高速恒星移动得如此之快，以至于大质量黑洞（如在银河系中心发现的）的动态抛射是它们唯一的起源，它们越来越被认为是理解大质量黑洞的历史、性质和环境的重要工具。此外，它们的速度如此之快，以至于它们与我们的银河系无关。虽然第一颗超高速恒星直到2005年才被发现，但最近已经有8颗恒星被发现（包括我们团队发现的4颗），它们的距离在20到110千公里之间。我们将开始系统地搜索从斯隆数字天空和汉堡巡天中提取的候选超高速蓝色恒星。为了明确它们的演化状态（年轻的大质量恒星或年老的低质量恒星）和它们的年龄，以及测量径向速度和距离，需要对高分辨率光谱进行定量分析。将进行天体测量来测量固有运动。从太空运动中，恒星穿过银河晕的路径将被重建。尽管游离于银河系的恒星最为壮观，但年轻的超高速恒星对约束银河系的弹射机制至关重要，而这种大年龄的恒星是银河系潜力的探测器，可以用来约束银河系的逃逸速度和银河系的质量。

We propose to study the newly discovered population of hyper-velocity stars in order to determine their true nature. Hyper-velocity stars move so fast that dynamical ejection from a massive black hole (as found e.g. in the Galactic centre) is their only suggested origin and they are becoming more and more recognized as an important tool to understand the history, nature and environment of massive black holes. Moreover, they travel with such extreme velocities that they are unbound to our Galaxy. Although the first hyper-velocity star was discovered only by 2005, already eight additional stars have been found recently (including 4 discoveries by our team) at distances as large as 20 to 110 kpc. We shall embark on a systematic search for candidate hyper-velocity blue stars to be drawn from the Sloan Digital Sky and Hamburg Surveys. Quantitative spectral analyses of high resolution spectra are required to clarify their evolutionary status (young massive or old low mass star) and their age as well as to measure the radial velocity and distance. Astrometry will be carried out to measure the proper motions. From the space motions the stellar path through the Galactic halo will be reconstructed. Although the stars unbound to the Galaxy are most spectacular, young hyper-velocity stars bound to the Galaxy are important to constrain the ejection mechanism, while such stars of large age are probes of the Galactic potential that can be used to constrain the Galactic escape velocity and the mass of the Galaxy.