An article accepted for publication in the journal “Astronomy and Astrophysics” reports a study on the star Zeta Ophiuchi, a so-called runaway star that became famous even beyond the field of astronomy for its bow shock, the enormous shock wave similar to the waves generated in the water by the bow of a ship. A team of researchers led by Samuel Green from the Institute for Advanced Studies in Dublin, Ireland, built detailed computer models of the bow shock to try to explain the observed data. The results confirm the origins of Zeta Ophiuchi but only partially explain the X-ray emissions detected.
At the end of 2012, the publication of images of the star Zeta Ophiuchi, or simply Z Oph, obtained thanks to observations conducted in particular using NASA’s Spitzer Space Telescope, allowed to admire its colossal bow shock. The reconstruction of Zeta Ophiuchi’s history indicated that it had a very massive companion whose supernova explosion pushed it away from its area of origin at a remarkable speed, technically a runaway star.
The history of Zeta Ophiuchi and its bow shock are interesting from a scientific point of view. Observing this giant blue star is relatively easy thanks to its relative proximity to Earth, estimated at about 440 light-years following observations conducted in recent years by ESA’s Gaia space probe. However, infrared and X-ray emissions require suitable instruments to obtain quality detections.
Computer models were created to try to reproduce the processes associated with runaway stars such as Zeta Ophiuchi. NASA’s Chandra X-ray Observatory provided more data about its X-ray emissions, which are the most difficult to explain. The image (X-ray: NASA/CXC/Dublin Inst. Advanced Studies/S. Green et al.; Infrared: NASA/JPL/Spitzer) shows a composition of the data from Chandra, in blue, and Spitzer, in green and red, showing Zeta Ophiuchi and its bow shock.
The simulations generated thanks to the models developed by the authors of this new study confirm that Zeta Ophiuchi was ejected from the area where it formed due to a companion that exploded in a supernova. The problem is that the X-rays detected, emitted by gases heated to temperatures of millions of degrees due to the bow shock wave, don’t match those predicted by the simulations. Three models approach the actual detections but one predicts X-ray emissions weaker than those detected while two others predict those emissions to be greater near the shock wave.
The researchers intend to continue developing the models to account for the effects of turbulence and particle acceleration in the bow shock. New quality observations of X-ray emissions would also help this type of study because the current ones are affected by the contamination caused by the stellar emissions, which make it difficult to assess which are generated by the bow shock. In the coming years, we can expect new advances to better understand the processes taking place around runaway stars like Zeta Ophiuchi that offer great cosmic shows.
