Colloquium on Apr. 19th, 2018

New insights on the X-ray Source Populations in Globular Clusters and Galaxy Clusters

Speaker:李志远（南京大学）/ Zhiyuan Li (Nanjing University)

Venue:Gewu 4410

Time:3:00 PM, Thursday, 19th April, 2018

Abstract:X-ray-emitting, close binary systems involving a black hole (BH), a neutron star (NS) or a white dwarf (WD), are among the first objects discovered in the X-ray sky and now understood to be ubiquitous in the Universe. As such, X-ray binaries can serve as a useful tool to study the evolution of their parent stellar populations, on scales from star clusters to galaxy clusters. In this talk, I will present our recent work on the X-ray populations in (i) Milky Way globular clusters, and (ii) the two nearest galaxy clusters (Virgo and Fornax), based primarily on Chandra observations. We show that the specific number of CVs (i.e. accreting WDs) in globular clusters is on average lower than that in the field, which can be understood as an efficient disruption of primordial binaries due to binary-single encounters. We also find observational evidence of mass segregation in globular clusters, which allows us to place constraints on the characteristic masses of CVs and other close binary systems. In Virgo and Fornax, we reveal the presence of intra-cluster X-ray sources, i.e., sources that are not associated with the member galaxies. The intra-cluster sources may have a mixed origin, including in particular the long-sought gravitationally recoiled massive black holes. This opens a new avenue for studying the structural growth of galaxy clusters.

Personal Information:

Zhiyuan Li is currently a Professor of Astronomy at Nanjing University. He obtained his Bachelor and Master degrees in Astronomy at NJU, his PhD degree in Astrophysics at the University of Massachusetts. He was then a postdoc at the Smithsonian Astrophysical Observatory and an assistant researcher at UCLA, before joining the faculty of NJU in 2013. His research is focused on high-energy astrophysics in the context of galaxy evolution, using a multi-wavelength approach.