These researchers have observed super massive black holes. This is impassible. Such theoretical objects do not exist in this physical reality. Only in the mind of some professional speculators.
Mathematical apparatus of theory of General relativity operate on the space as geometric object and do not consider the cosmic vacuum which fill the space and is real physical environment with certain properties and limitations. It is a transmission medium that allows movement and controls the behavior of elementary particles and carries electromagnetic waves. In the visible universe there is no such thing like empty space. This is the main reason why GR have noting to do with reality where exist absolutes.