Tour: Embracing a Rejected Star

Zeta Ophiuchi is a star with a complicated past, having likely been ejected from its birthplace by a powerful stellar explosion. A new look by NASA's Chandra X-ray Observatory helps tell more of the story of this runaway star.

Located about 440 light-years from Earth, Zeta Ophiuchi is a hot star that is 20 times more massive than the Sun. Previous observations have provided evidence that Zeta Ophiuchi was once in close orbit with another star, before being ejected when this companion was destroyed in a supernova explosion. Infrared data from NASA's Spitzer Space Telescope reveal a spectacular shock wave that was formed by matter blowing away from the star's surface and slamming into gas in its path. Data from Chandra show a bubble of X-ray emission located around the star, produced by gas that has been heated by the shock wave to tens of millions of degrees.

Outlined in a recent paper, researchers have constructed the first detailed computer models of the shock wave. They have begun testing whether the models can explain the data obtained at different wavelengths, including X-ray, optical, infrared and radio observations. All three of the different computer models predict fainter X-ray emission than observed. The bubble of X-ray emission is brightest near the star, whereas two of the three computer models predict the X-ray emission should be brighter near the shock wave.

In the future researchers plan to test more complicated models with additional physics — including the effects of turbulence, and particle acceleration — to see whether the agreement with X-ray data will improve.