SUPER-MASSIVE BLACK HOLE SPEEDS UP TO SUPERSONIC CRUISING VELOCITY 

Using the recently commissioned Sardinia Radio Telescope (SRT) a team of astronomers have produced a new radio image of a super-massive black hole diving into the core of the distant cluster of galaxies designed as 3C 129.

The black hole sits at the center of an elliptical galaxy some at 300 million light years from Earth.

Image caption: These false colour images show the cluster of galaxy 3C 129 at radio, X-ray, and near-infrared bands. Left: superposition of the SRT image at 6.6 GHz (red) with the X-ray emission of the hot intracluster medim (blue). Top-right: Very Large Array image at 1.4 GHz. Bottom-right: high-resolution VLA image at 4.7 GHz (red) overlayed to an image of the black hole host galaxy in the near-infrared (Credits: NRAO; ROSAT satellite; the Two Micron All Sky Survey).

The black hole and its galaxy are in 'route of collision' with a nearby galaxy cluster, pulled by the gravitational force generated by the huge concentration of dark matter, galaxies, and hot gas.

The radio images reveal that the black hole is actively accreting matter. Part of this material is not falling into the black hole but expelled into two streams of plasma that are bent back by the ram pressure exerted by the intergalactic gas into a spectacular tail much longer than the size of the galaxy itself.

“The phenomenon is quite likely a jet contrail,” says Matteo Murgia, lead author of the study that will be published in the journal Montly Notices of the Royal Astronomical Society. “There are however some notable differences. In the case of the black hole jets, the 'unburned fuel' consists of a  plasma composed by mixture of high-energy electrons and magnetic fields that cools down by emitting radio waves. By using the new radio images acquired with the SRT in combination with observations performed with other radio telescopes, we were able to measure the cooling time of the plasma and to obtain for the first time a map of the age of this radio source.  By analyzing this map we have been able to confirm that the black hole is cruising at supersonic speed (M=1.5), as previoulsy suggested by other authors based on observation of a shock front structure preceding the galaxy.”

Image caption: three color composite images of 3C129 obtained at 0.3 GHz (WENSS; red), 1.4 GHz (VLA; green), and 6.6 GHz (SRT; blue). The color turns smoothly from bluish to redish as a result of the intense radiative cooling of the radio-emitting plasma wake. 

The SRT is also capable to observe the radio sky in 'polarized light'. The degree of polarization of the radio waves is an important information for the astronomers since can yield insights into the strength and orientation of magnetic fields in astrophysical objects and the associated foregrounds. Close to the black hole the flow is turbulent and wavy with a very low polarized emission, but moving along the plasma wake the polarization level increases revealing highly ordered magnetic fields.

Image caption: SRT image of 3C129 at 6.6 GHz in polarized light. The lenght of the vectors is proportional to the polarized intensity while their orientation represens the polarization angle.

“This study represents the first published scientific results for the SRT”,  says Ettore Carretti, SRT Officer-in-Charge and co-author of the study. “It demostrates that the SRT is ready to produce high-quality and wide-field images of the radio sky, even in polarization. We are extremely satisfied, we did not expect to get such beautiful results so early in the commissioning phase. Each radio telescope has polarization impurities arising from structural asymmetries and errors in manufacturing. The amount of spurious polarization typically is of the order of a few percent and thus is of the same order as the typical degree of polarization in the observed sources and so needs to be carefully calibrated. Our results demostrate that the SRT is characterized by very good polarization performances and is ready for these challenging observations.”

"The SRT is among the largest and most sensitive radio telescopes in the world and it is exciting to see early results being produced that verify its scientific performance. This will be the first of many new discoveries to come from this telescope", says Professor Steven Tingay, Head of the Radio Astronomy Section in the INAF Science Directorate.

“These fascinating images illustrate the capabilities of the SRT used in conjunction with the new state-of-the-art SARDARA backend”, says Andrea Possenti,  Director of the Cagliari Astonomical Observatory and PI of the SARDARA project, funded by the Sardinian Regional Government. “These results”, underlines Possenti,  “have been possible thanks to the joint efforts of the SRT Astronomical Validation team and the SARDARA backend developers, two tight-knit teams comprised of astronomers and technologists of INAF.”