Supermassive black holes in the centers of galaxies are not something very surprising to modern astronomers. For example, we have one at the central point of our own Milky Way galaxy. But the origin of these enormous objects is still a missing link required to explain the growth of black holes, as well as formation and evolution of galaxies. Studies in this field are gaining a momentum, and the first results are starting to emerge.

An international team of scientists from University of La Laguna, Spain, University of Durham, UK, and Max Planck Institute for Radio Astronomy, Germany, presented their research involving analysis of ultraluminous X-ray sources (ULXs). The authors have published a paper at arXiv.org,. They propose an idea that ULXs are perfect candidates to look for so-called intermediate-mass black holes, which hypothetically could be the predecessors of their supermassive counterparts.

So where should we look for those ultraluminous sources of X-rays? Astronomers say ULXs are typically associated with galactic star-forming regions and sometimes are a part of optical and radio nebulae produced by energy radiated from particular ULX. Some of the extreme X-ray sources, which are located in the nearby spiral galaxies, also show properties which are similar to certain types of black holes, i.e. sub-Eddington accreting black holes.

According to the authors, if the intermediate-mass black hole is the cause of a certain ULX, this ultraluminous X-ray source should emit steady radio jets, produced by the black hole. In order to verify this assumption, the scientists performed observations of seven ULXs in the frequency range of 5 GHz using NRAO’s Extended Very Large Array radiotelescope system.

Radio emissions consistent with theoretical presence of intermediate-mass black hole were not detected in six of seven observed targets, although the authors say the upper limits of the radio flux densities make the supermassive black hole presence possible. One source of radio emissions, which is located in NGC 2276, indicated a possible presence of central black hole. On the other hand, two scenarios are possible: either these emissions are caused by an extraordinary powerful ultraluminous source of X-rays, or they are generated by an intermediate-mass black hole, which at some point in the distant future could evolve into a supermassive black hole with its own (or stolen via tidal stripping) galaxy.

The team hopes to perform some follow-up radio observations of NGC 2276 and other potential new targets using the VLBI technique.

By Alius Noreika, source: Technology.org