While symbiotic novae are rare objects themselves, observing a symbiotic nova like V407 Cygni in gamma rays was an absolute breakthrough. The researchers went then in search of evidence indicating the presence of shocks, passing through the material in the form of shock waves, due to the very energetic physical processes involved in the event. Never before so detailed radio-band images reveal the shock produced by the explosion of the material on the surface of the white dwarf as it expands into the atmosphere of the red giant companion.
“Novae, with their sudden increases in visible light emission, have fascinated astronomers for centuries and their revelation in gamma rays has been a great surprise,” says Giroletti. “Having been able to witness, thanks to radio waves, not only the increase in brightness, but also the choreography produced by the interaction of these two stars is a very exciting result, and one of great scientific value.”
The new observations were possible thanks to the very high level of detail obtained in the radio band by the VLBI (Very Long Baseline Interferometry) technique, which made it possible to directly visualize the appearance and propagation of the shock.
While demonstrating for the first time in a direct way the presence of the shock in this type of events, the researchers were also able to understand how the source is oriented: the red giant is in the foreground in front of the white dwarf, and from the latter two opposite jets depart, in the plane of the sky, perpendicular to the line of sight.
The observations also allowed researchers to reveal traces of previous events in the life of this binary star, one around 2003, one even dating back to the 1930s. A step forward in understanding the evolution of these rare objects.
These results are the outcome of an intense and ambitious observational campaign. The data from the European VLBI Network (EVN) were streamed in real-time to the central data processor (correlator) at JIVE, a European Research Infrastructure Consortium in Dwingeloo, the Netherlands. A super computer combined the data obtained simultaneously from all the antennas of the network, and this allowed the researchers to understand right away that this was really an unmissable event.