Emission Lines and Black-Hole Acitivity in Extragalactic Globular Clusters

泽普夫博士将继续他的偶然发现，即在室女座星系团的椭圆星系中的一个球状星团的光谱中，意外发现了一个变化剧烈的X射线源和一条非常宽的光学发射线。除了气体坠入黑洞的信号外，很难将这两个观测结果解释为其他信号。该小组将获得更广泛的光谱覆盖范围，以确定谱线比率，从而确定发射气体可能是光电离的还是冲击电离的。这与可能的黑洞的质量有关：恒星质量的黑洞可能会产生激波电离，而质量更大的黑洞则会光致电离气体。其他球状星团将被搜索以寻找类似的信号。这项工作具有潜在的变革性，因为它可能为中等质量黑洞提供迄今最确凿的证据：这些物体质量如此之大，以至于一颗垂死的恒星的爆炸都无法产生它们。如果发现中等质量黑洞是在球状星团中形成的，这将开启一个新的研究领域。学生将在参与这项研究的同时接受培训。泽普夫博士将就他的工作进行公开演讲，并将结果纳入他的概论调查课程的教学中。

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.