As explained by another author of the research, an astronomer at the University
of Michigan, Marta Volonteri, "We had reason to expect that black holes
exist in many of the early galaxies, but so far they had escaped our
search." In fact, it was anticipated that a population of black holes "baby"
existed in the early universe, but this population had not been observed so
far.
The main difficulty in studying black holes is that they are almost all
surrounded by dense clouds of gas and dust, so that optical telescopes can’t
detect them. However, the X-ray light high energy it can penetrate these
clouds, and allow to study what they hide.
