Emission Lines and Black-Hole Acitivity in Extragalactic Globular Clusters

Zepf博士将继续他在室女座星系团椭圆星系中的球状星团的光谱中发现剧烈变化的x射线源和非常宽的光学发射线的偶然发现。很难解释这两个观测结果，除非它们是气体落入黑洞的标志。该小组将获得更广泛的光谱覆盖范围，以确定线比，从而确定发射气体可能是光电离还是激波电离。这与可能的黑洞的质量有关：一个恒星质量的黑洞可能会产生激波电离，而一个更大质量的黑洞会光电离气体。其他球状星团也会被寻找类似的特征。这项工作具有潜在的革命性，因为它可以为中等质量黑洞提供最可靠的证据：这些物体如此之大，以至于单个垂死恒星的爆炸无法产生它们。如果发现中等质量的黑洞在球状星团中形成，这将打开一个新的研究领域。学生将在参与这项研究的过程中接受培训。Zepf博士将公开演讲他的工作，并将结果纳入他的入门调查课程的教学中。

Dr. Zepf will follow up his serendipitous discovery of a violently variable X-ray source and a very broad optical emission line in the spectrum of a globular star cluster in elliptical galaxy in the Virgo Cluster of galaxies. It is difficult to interpret these two observations other than as signatures of a black hole into which gas is falling. The group will obtain wider spectral coverage to determine line ratios and hence whether the emitting gas is likely to be photo-ionized or shock-ionized. This bears on the mass of the likely black hole: a stellar-mass black hole is likely to produce shock-ionization, while a more massive black hole would photo-ionize the gas. Other globular star clusters would be searched for similar signatures. This work is potentially transformative, as it could provide the most solid evidence yet for intermediate-mass black holes: these objects are so massive that the explosion of a single dying star cannot make them. If intermediate-mass black holes are found to form in globular clusters, this will open a new area of research. Students will be trained as they participate in this research. Dr. Zepf will give public lectures on his work, and incorporate the results into his teaching of introductory survey classes.