Using the brand-new Sardinia Radio Telescope (SRT), a giant parabolic dish of 64 meters diameter, a team of astronomers from the Italian National Institute for Astrophysics (INAF) and the University of Cagliari have produced a detailed image of a super-massive black hole proceeding at high speed  towards the core of the distant cluster of galaxies designed as 3C 129. The results are going to be published in the scientific journal Monthly Notices of the Royal Astronomical Society.

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

Image caption: These false color 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 medium (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 collision course 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 merge to form a spectacular tail much longer than the size of the galaxy itself.

"The phenomenon is quite likely a jet contrail," says Matteo Murgia researcher at the INAF - Astronomical Observatory of Cagliari, lead author of the study. "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 comparing the new SRT observations with those performed with other radio telescopes, we were able to obtain for the first time a map of the age of this radio source and to conclude that the black hole is cruising at supersonic speed."

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.

In the Earth's atmosphere the sound speed is about 1,200 km/h, but in the 'atmosphere' of the cluster of galaxy surrounding the black hole, an ultra-rarefied gas at a temperature of tens of millions of degrees Kelvin, the sound speed is as high as 4 million km/h. The black hole is traveling at a speed as much as 1.5 times this limit.

"A further peculiarity of this black hole – continues Matteo Murgia – is the presence of a shock wave in front of the galaxy, very similar to those associated to combat aircrafts. With some surprise, we found that the black hole speed we measured is exactly the one previously theorized to explain the presence of the shock wave."

The SRT is also capable to observe the radio sky in 'polarized light'. The degree of polarization of the radio waves is an important source of information for the astronomers since can yield insights into the strength and orientation of magnetic fields in astrophysical objects. 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 length of the line segments is proportional to the polarized intensity while their orientation represents the polarization angle.

"This study is the first paper on a scientific results from the SRT", says Ettore Carretti, SRT Officer-in-Charge and co-author of the study. “It shows that the SRT is ready to produce high quality images of the radio sky even in polarization, that usually is challenging and left as last step to setup in a new facility. It is clear indication of the maturity of the telescope performance now ready to deliver the great and challenging science it was built for."

"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 Astronomical Observatory of Cagliari 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 INAF scientists."

The paper online:

Sardinia Radio Telescope wide-band spectral-polarimetric observations of the galaxy cluster 3C 129 by M. Murgia, F. Govoni, E. Carretti, A. Melis, R. Concu, A. Trois, F. Loi, V. Vacca, A. Tarchi, P. Castangia, A. Possenti, A. Bocchinu, M. Burgay, S. Casu, A. Pellizzoni, T. Pisanu, A. Poddighe, S. Poppi, N. D’Amico, M. Bachetti, A. Corongiu, E. Egron, N. Iacolina, A. Ladu, P. Marongiu, C. Migoni, D. Perrodin, M. Pilia, G. Valente, and G. Vargiu to appear on Monthly Notices of the Royal Astronomical Society

About SRT

The SRT is a brand-new 64-m diameter radio telescope located 35-km north of Cagliari, Italy.The SRT is funded by the Ministry of Instruction, of University, and Research (MIUR), Italian Space Agency (ASI), and the Autonomous Region of Sardinia (RAS) and is operated as National Facility by the National Institute for Astrophysics (INAF).

Image caption: the Sardinia Radio Telescope at night (Credits INAF).

The telescope is capable to operate with high efficiency in the frequency range from 0.3 to 116 GHz also thanks to its active surface: the primary mirror is composed by 1008 panels that are digitally controlled to compensate for gravitational deformations. The antenna officially opened in 2013 upon completion of the technical commissioning phase.  Then, the Astronomical Validation team  started the scientific commissioning activities, transforming a powerful technological instrument to a real radio astronomical facility. In February 2016 the SRT was opened in shared-risk mode for a first Early Science Program call.

The SRT is equipped with state-of-the-art backend electronics. In this work, we exploited for the first time the capabilities of the recently-commissioned SARDARA (SArdinia Roach2-based Digital Architecture for Radio Astronomy) backend. The development of the SARDARA backend has been funded by the Autonomous Region of Sardinia (RAS) using resources from the Regional Law 7/2007 ”Promotion of the scientific research and technological innovation in Sardinia”.